New pthread rwlock that is more scalable.

This replaces the pthread rwlock with a new implementation that uses a
more scalable algorithm (primarily through not using a critical section
anymore to make state changes).  The fast path for rdlock acquisition and
release is now basically a single atomic read-modify write or CAS and a few
branches.  See nptl/pthread_rwlock_common.c for details.

	* nptl/DESIGN-rwlock.txt: Remove.
	* nptl/lowlevelrwlock.sym: Remove.
	* nptl/Makefile: Add new tests.
	* nptl/pthread_rwlock_common.c: New file.  Contains the new rwlock.
	* nptl/pthreadP.h (PTHREAD_RWLOCK_PREFER_READER_P): Remove.
	(PTHREAD_RWLOCK_WRPHASE, PTHREAD_RWLOCK_WRLOCKED,
	PTHREAD_RWLOCK_RWAITING, PTHREAD_RWLOCK_READER_SHIFT,
	PTHREAD_RWLOCK_READER_OVERFLOW, PTHREAD_RWLOCK_WRHANDOVER,
	PTHREAD_RWLOCK_FUTEX_USED): New.
	* nptl/pthread_rwlock_init.c (__pthread_rwlock_init): Adapt to new
	implementation.
	* nptl/pthread_rwlock_rdlock.c (__pthread_rwlock_rdlock_slow): Remove.
	(__pthread_rwlock_rdlock): Adapt.
	* nptl/pthread_rwlock_timedrdlock.c
	(pthread_rwlock_timedrdlock): Adapt.
	* nptl/pthread_rwlock_timedwrlock.c
	(pthread_rwlock_timedwrlock): Adapt.
	* nptl/pthread_rwlock_trywrlock.c (pthread_rwlock_trywrlock): Adapt.
	* nptl/pthread_rwlock_tryrdlock.c (pthread_rwlock_tryrdlock): Adapt.
	* nptl/pthread_rwlock_unlock.c (pthread_rwlock_unlock): Adapt.
	* nptl/pthread_rwlock_wrlock.c (__pthread_rwlock_wrlock_slow): Remove.
	(__pthread_rwlock_wrlock): Adapt.
	* nptl/tst-rwlock10.c: Adapt.
	* nptl/tst-rwlock11.c: Adapt.
	* nptl/tst-rwlock17.c: New file.
	* nptl/tst-rwlock18.c: New file.
	* nptl/tst-rwlock19.c: New file.
	* nptl/tst-rwlock2b.c: New file.
	* nptl/tst-rwlock8.c: Adapt.
	* nptl/tst-rwlock9.c: Adapt.
	* sysdeps/aarch64/nptl/bits/pthreadtypes.h (pthread_rwlock_t): Adapt.
	* sysdeps/arm/nptl/bits/pthreadtypes.h (pthread_rwlock_t): Adapt.
	* sysdeps/hppa/nptl/bits/pthreadtypes.h (pthread_rwlock_t): Adapt.
	* sysdeps/ia64/nptl/bits/pthreadtypes.h (pthread_rwlock_t): Adapt.
	* sysdeps/m68k/nptl/bits/pthreadtypes.h (pthread_rwlock_t): Adapt.
	* sysdeps/microblaze/nptl/bits/pthreadtypes.h (pthread_rwlock_t): Adapt.
	* sysdeps/mips/nptl/bits/pthreadtypes.h (pthread_rwlock_t): Adapt.
	* sysdeps/nios2/nptl/bits/pthreadtypes.h (pthread_rwlock_t): Adapt.
	* sysdeps/s390/nptl/bits/pthreadtypes.h (pthread_rwlock_t): Adapt.
	* sysdeps/sh/nptl/bits/pthreadtypes.h (pthread_rwlock_t): Adapt.
	* sysdeps/sparc/nptl/bits/pthreadtypes.h (pthread_rwlock_t): Adapt.
	* sysdeps/tile/nptl/bits/pthreadtypes.h (pthread_rwlock_t): Adapt.
	* sysdeps/unix/sysv/linux/alpha/bits/pthreadtypes.h
	(pthread_rwlock_t): Adapt.
	* sysdeps/unix/sysv/linux/powerpc/bits/pthreadtypes.h
	(pthread_rwlock_t): Adapt.
	* sysdeps/x86/bits/pthreadtypes.h (pthread_rwlock_t): Adapt.
	* nptl/nptl-printers.py (): Adapt.
	* nptl/nptl_lock_constants.pysym: Adapt.
	* nptl/test-rwlock-printers.py: Adapt.
	* nptl/test-rwlockattr-printers.c: Adapt.
	* nptl/test-rwlockattr-printers.py: Adapt.

26 files changed, 1348 insertions, 770 deletions

diff --git a/nptl/DESIGN-rwlock.txt b/nptl/DESIGN-rwlock.txt
deleted file mode 100644
index 810d1b8f35..0000000000
--- a/nptl/DESIGN-rwlock.txt
+++ /dev/null
@@ -1,113 +0,0 @@
-Reader Writer Locks pseudocode
-==============================
-
-	pthread_rwlock_rdlock(pthread_rwlock_t *rwlock);
-	pthread_rwlock_unlock(pthread_rwlock_t *rwlock);
-	pthread_rwlock_wrlock(pthread_rwlock_t *rwlock);
-
-struct pthread_rwlock_t {
-
-   unsigned int lock:
-         - internal mutex
-
-   unsigned int writers_preferred;
-         - locking mode: 0 recursive, readers preferred
-                         1 nonrecursive, writers preferred
-
-   unsigned int readers;
-         - number of read-only references various threads have
-
-   pthread_t writer;
-         - descriptor of the writer or 0
-
-   unsigned int readers_wakeup;
-         - 'all readers should wake up' futex.
-
-   unsigned int writer_wakeup;
-         - 'one writer should wake up' futex.
-
-   unsigned int nr_readers_queued;
-         - number of readers queued up.
-
-   unsigned int nr_writers_queued;
-         - number of writers queued up.
-}
-
-pthread_rwlock_rdlock(pthread_rwlock_t *rwlock)
-{
-  lll_lock(rwlock->lock);
-  for (;;) {
-    if (!rwlock->writer && (!rwlock->nr_writers_queued ||
-					!rwlock->writers_preferred))
-        break;
-
-    rwlock->nr_readers_queued++;
-    val = rwlock->readers_wakeup;
-    lll_unlock(rwlock->lock);
-
-    futex_wait(&rwlock->readers_wakeup, val)
-
-    lll_lock(rwlock->lock);
-    rwlock->nr_readers_queued--;
-  }
-  rwlock->readers++;
-  lll_unlock(rwlock->lock);
-}
-
-pthread_rwlock_tryrdlock(pthread_rwlock_t *rwlock)
-{
-  int result = EBUSY;
-  lll_lock(rwlock->lock);
-  if (!rwlock->writer && (!rwlock->nr_writers_queued ||
-					!rwlock->writers_preferred))
-    rwlock->readers++;
-  lll_unlock(rwlock->lock);
-  return result;
-}
-
-pthread_rwlock_wrlock(pthread_rwlock_t *rwlock)
-{
-  lll_lock(rwlock->lock);
-  for (;;) {
-    if (!rwlock->writer && !rwlock->readers)
-       break;
-
-    rwlock->nr_writers_queued++;
-    val = rwlock->writer_wakeup;
-    lll_unlock(rwlock->lock);
-
-    futex_wait(&rwlock->writer_wakeup, val);
-
-    lll_lock(rwlock->lock);
-    rwlock->nr_writers_queued--;
-  }
-  rwlock->writer = pthread_self();
-  lll_unlock(rwlock->lock);
-}
-
-pthread_rwlock_unlock(pthread_rwlock_t *rwlock)
-{
-  lll_lock(rwlock->lock);
-
-  if (rwlock->writer)
-    rwlock->writer = 0;
-  else
-    rwlock->readers--;
-
-  if (!rwlock->readers) {
-    if (rwlock->nr_writers_queued) {
-      ++rwlock->writer_wakeup;
-      lll_unlock(rwlock->lock);
-      futex_wake(&rwlock->writer_wakeup, 1);
-      return;
-    } else
-      if (rwlock->nr_readers_queued) {
-        ++rwlock->readers_wakeup;
-        lll_unlock(rwlock->lock);
-        futex_wake(&rwlock->readers_wakeup, MAX_INT);
-        return;
-      }
-  }
-
-  lll_unlock(rwlock->lock);
-}
diff --git a/nptl/Makefile b/nptl/Makefile
index 36dbdbb54c..9d5738f270 100644
--- a/nptl/Makefile
+++ b/nptl/Makefile
@@ -237,10 +237,11 @@ tests = tst-typesizes \
 	tst-robust6 tst-robust7 tst-robust8 tst-robust9 \
 	tst-robustpi1 tst-robustpi2 tst-robustpi3 tst-robustpi4 tst-robustpi5 \
 	tst-robustpi6 tst-robustpi7 tst-robustpi8 tst-robustpi9 \
-	tst-rwlock1 tst-rwlock2 tst-rwlock2a tst-rwlock3 tst-rwlock4 \
-	tst-rwlock5 tst-rwlock6 tst-rwlock7 tst-rwlock8 tst-rwlock9 \
-	tst-rwlock10 tst-rwlock11 tst-rwlock12 tst-rwlock13 tst-rwlock14 \
-	tst-rwlock15 tst-rwlock16 \
+	tst-rwlock1 tst-rwlock2 tst-rwlock2a tst-rwlock2b tst-rwlock3 \
+	tst-rwlock4 tst-rwlock5 tst-rwlock6 tst-rwlock7 tst-rwlock8 \
+	tst-rwlock9 tst-rwlock10 tst-rwlock11 tst-rwlock12 tst-rwlock13 \
+	tst-rwlock14 tst-rwlock15 tst-rwlock16 tst-rwlock17 tst-rwlock18 \
+	tst-rwlock19 \
 	tst-once1 tst-once2 tst-once3 tst-once4 tst-once5 \
 	tst-key1 tst-key2 tst-key3 tst-key4 \
 	tst-sem1 tst-sem2 tst-sem3 tst-sem4 tst-sem5 tst-sem6 tst-sem7 \
@@ -306,7 +307,7 @@ test-xfail-tst-once5 = yes
 # Files which must not be linked with libpthread.
 tests-nolibpthread = tst-unload
 
-gen-as-const-headers = pthread-errnos.sym lowlevelrwlock.sym \
+gen-as-const-headers = pthread-errnos.sym \
 		       unwindbuf.sym \
 		       lowlevelrobustlock.sym pthread-pi-defines.sym
 
diff --git a/nptl/lowlevelrwlock.sym b/nptl/lowlevelrwlock.sym
deleted file mode 100644
index f50b25bfb8..0000000000
--- a/nptl/lowlevelrwlock.sym
+++ /dev/null
@@ -1,16 +0,0 @@
-#include <stddef.h>
-#include <stdio.h>
-#include <bits/pthreadtypes.h>
-#include <bits/wordsize.h>
-
---
-
-MUTEX		offsetof (pthread_rwlock_t, __data.__lock)
-NR_READERS	offsetof (pthread_rwlock_t, __data.__nr_readers)
-READERS_WAKEUP	offsetof (pthread_rwlock_t, __data.__readers_wakeup)
-WRITERS_WAKEUP	offsetof (pthread_rwlock_t, __data.__writer_wakeup)
-READERS_QUEUED	offsetof (pthread_rwlock_t, __data.__nr_readers_queued)
-WRITERS_QUEUED	offsetof (pthread_rwlock_t, __data.__nr_writers_queued)
-FLAGS		offsetof (pthread_rwlock_t, __data.__flags)
-WRITER		offsetof (pthread_rwlock_t, __data.__writer)
-PSHARED		offsetof (pthread_rwlock_t, __data.__shared)
diff --git a/nptl/nptl-printers.py b/nptl/nptl-printers.py
index 77018e7ea7..9d67865577 100644
--- a/nptl/nptl-printers.py
+++ b/nptl/nptl-printers.py
@@ -430,12 +430,10 @@ class RWLockPrinter(object):
         """
 
         data = rwlock['__data']
-        self.readers = data['__nr_readers']
-        self.queued_readers = data['__nr_readers_queued']
-        self.queued_writers = data['__nr_writers_queued']
-        self.writer_id = data['__writer']
+        self.readers = data['__readers']
+        self.cur_writer = data['__cur_writer']
         self.shared = data['__shared']
-        self.prefers_writers = data['__flags']
+        self.flags = data['__flags']
         self.values = []
         self.read_values()
 
@@ -468,20 +466,19 @@ class RWLockPrinter(object):
     def read_status(self):
         """Read the status of the rwlock."""
 
-        # Right now pthread_rwlock_destroy doesn't do anything, so there's no
-        # way to check if an rwlock is destroyed.
-
-        if self.writer_id:
-            self.values.append(('Status', 'Locked (Write)'))
-            self.values.append(('Writer ID', self.writer_id))
-        elif self.readers:
-            self.values.append(('Status', 'Locked (Read)'))
-            self.values.append(('Readers', self.readers))
+        if self.readers & PTHREAD_RWLOCK_WRPHASE:
+            if self.readers & PTHREAD_RWLOCK_WRLOCKED:
+                self.values.append(('Status', 'Acquired (Write)'))
+                self.values.append(('Writer ID', self.cur_writer))
+            else:
+                self.values.append(('Status', 'Not acquired'))
         else:
-            self.values.append(('Status', 'Unlocked'))
-
-        self.values.append(('Queued readers', self.queued_readers))
-        self.values.append(('Queued writers', self.queued_writers))
+            r = self.readers >> PTHREAD_RWLOCK_READER_SHIFT
+            if r > 0:
+                self.values.append(('Status', 'Acquired (Read)'))
+                self.values.append(('Readers', r))
+            else:
+                self.values.append(('Status', 'Not acquired'))
 
     def read_attributes(self):
         """Read the attributes of the rwlock."""
@@ -491,10 +488,12 @@ class RWLockPrinter(object):
         else:
             self.values.append(('Shared', 'No'))
 
-        if self.prefers_writers:
+        if self.flags == PTHREAD_RWLOCK_PREFER_READER_NP:
+            self.values.append(('Prefers', 'Readers'))
+        elif self.flags == PTHREAD_RWLOCK_PREFER_WRITER_NP:
             self.values.append(('Prefers', 'Writers'))
         else:
-            self.values.append(('Prefers', 'Readers'))
+            self.values.append(('Prefers', 'Writers no recursive readers'))
 
 class RWLockAttributesPrinter(object):
     """Pretty printer for pthread_rwlockattr_t.
@@ -555,13 +554,12 @@ class RWLockAttributesPrinter(object):
             # PTHREAD_PROCESS_PRIVATE
             self.values.append(('Shared', 'No'))
 
-        if (rwlock_type == PTHREAD_RWLOCK_PREFER_READER_NP or
-            rwlock_type == PTHREAD_RWLOCK_PREFER_WRITER_NP):
-            # This is a known bug.  Using PTHREAD_RWLOCK_PREFER_WRITER_NP will
-            # still make the rwlock prefer readers.
+        if rwlock_type == PTHREAD_RWLOCK_PREFER_READER_NP:
             self.values.append(('Prefers', 'Readers'))
-        elif rwlock_type == PTHREAD_RWLOCK_PREFER_WRITER_NONRECURSIVE_NP:
+        elif rwlock_type == PTHREAD_RWLOCK_PREFER_WRITER_NP:
             self.values.append(('Prefers', 'Writers'))
+        else:
+            self.values.append(('Prefers', 'Writers no recursive readers'))
 
 def register(objfile):
     """Register the pretty printers within the given objfile."""
diff --git a/nptl/nptl_lock_constants.pysym b/nptl/nptl_lock_constants.pysym
index 2ab3179155..ade4398e0c 100644
--- a/nptl/nptl_lock_constants.pysym
+++ b/nptl/nptl_lock_constants.pysym
@@ -57,6 +57,11 @@ PTHREAD_RWLOCK_PREFER_READER_NP
 PTHREAD_RWLOCK_PREFER_WRITER_NP
 PTHREAD_RWLOCK_PREFER_WRITER_NONRECURSIVE_NP
 
+-- Rwlock
+PTHREAD_RWLOCK_WRPHASE
+PTHREAD_RWLOCK_WRLOCKED
+PTHREAD_RWLOCK_READER_SHIFT
+
 -- 'Shared' attribute values
 PTHREAD_PROCESS_PRIVATE
 PTHREAD_PROCESS_SHARED
diff --git a/nptl/pthreadP.h b/nptl/pthreadP.h
index 2322c59fa7..4f76cbb62a 100644
--- a/nptl/pthreadP.h
+++ b/nptl/pthreadP.h
@@ -150,9 +150,16 @@ enum
    | PTHREAD_MUTEXATTR_PROTOCOL_MASK | PTHREAD_MUTEXATTR_PRIO_CEILING_MASK)
 
 
-/* Check whether rwlock prefers readers.   */
-#define PTHREAD_RWLOCK_PREFER_READER_P(rwlock) \
-  ((rwlock)->__data.__flags == 0)
+/* For the following, see pthread_rwlock_common.c.  */
+#define PTHREAD_RWLOCK_WRPHASE		1
+#define PTHREAD_RWLOCK_WRLOCKED		2
+#define PTHREAD_RWLOCK_RWAITING		4
+#define PTHREAD_RWLOCK_READER_SHIFT	3
+#define PTHREAD_RWLOCK_READER_OVERFLOW	((unsigned int) 1 \
+					 << (sizeof (unsigned int) * 8 - 1))
+#define PTHREAD_RWLOCK_WRHANDOVER	((unsigned int) 1 \
+					 << (sizeof (unsigned int) * 8 - 1))
+#define PTHREAD_RWLOCK_FUTEX_USED	2
 
 
 /* Bits used in robust mutex implementation.  */
diff --git a/nptl/pthread_rwlock_common.c b/nptl/pthread_rwlock_common.c
new file mode 100644
index 0000000000..256508ca2a
--- /dev/null
+++ b/nptl/pthread_rwlock_common.c
@@ -0,0 +1,924 @@
+/* POSIX reader--writer lock: core parts.
+   Copyright (C) 2016-2017 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.	 See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <http://www.gnu.org/licenses/>.  */
+
+#include <errno.h>
+#include <sysdep.h>
+#include <pthread.h>
+#include <pthreadP.h>
+#include <sys/time.h>
+#include <stap-probe.h>
+#include <atomic.h>
+#include <futex-internal.h>
+
+
+/* A reader--writer lock that fulfills the POSIX requirements (but operations
+   on this lock are not necessarily full barriers, as one may interpret the
+   POSIX requirement about "synchronizing memory").  All critical sections are
+   in a total order, writers synchronize with prior writers and readers, and
+   readers synchronize with prior writers.
+
+   A thread is allowed to acquire a read lock recursively (i.e., have rdlock
+   critical sections that overlap in sequenced-before) unless the kind of the
+   rwlock is set to PTHREAD_RWLOCK_PREFER_WRITERS_NONRECURSIVE_NP.
+
+   This lock is built so that workloads of mostly readers can be executed with
+   low runtime overheads.  This matches that the default kind of the lock is
+   PTHREAD_RWLOCK_PREFER_READER_NP.  Acquiring a read lock requires a single
+   atomic addition if the lock is or was previously acquired by other
+   readers; releasing the lock is a single CAS if there are no concurrent
+   writers.
+   Workloads consisting of mostly writers are of secondary importance.
+   An uncontended write lock acquisition is as fast as for a normal
+   exclusive mutex but writer contention is somewhat more costly due to
+   keeping track of the exact number of writers.  If the rwlock kind requests
+   writers to be preferred (i.e., PTHREAD_RWLOCK_PREFER_WRITERS_NP or the
+   no-recursive-readers variant of it), then writer--to--writer lock ownership
+   hand-over is fairly fast and bypasses lock acquisition attempts by readers.
+   The costs of lock ownership transfer between readers and writers vary.  If
+   the program asserts that there are no recursive readers and writers are
+   preferred, then write lock acquisition attempts will block subsequent read
+   lock acquisition attempts, so that new incoming readers do not prolong a
+   phase in which readers have acquired the lock.
+
+
+   The main components of the rwlock are a writer-only lock that allows only
+   one of the concurrent writers to be the primary writer, and a
+   single-writer-multiple-readers lock that decides between read phases, in
+   which readers have acquired the rwlock, and write phases in which a primary
+   writer or a sequence of different primary writers have acquired the rwlock.
+
+   The single-writer-multiple-readers lock is the central piece of state
+   describing the rwlock and is encoded in the __readers field (see below for
+   a detailed explanation):
+
+   State WP  WL  R   RW  Notes
+   ---------------------------
+   #1    0   0   0   0   Lock is idle (and in a read phase).
+   #2    0   0   >0  0   Readers have acquired the lock.
+   #3    0   1   0   0   Lock is not acquired; a writer is waiting for a write
+			 phase to start or will try to start one.
+   #4    0   1   >0  0   Readers have acquired the lock; a writer is waiting
+			 and explicit hand-over to the writer is required.
+   #4a   0   1   >0  1   Same as #4 except that there are further readers
+			 waiting because the writer is to be preferred.
+   #5    1   0   0   0   Lock is idle (and in a write phase).
+   #6    1   0   >0  0   Write phase; readers are waiting for a read phase to
+			 start or will try to start one.
+   #7    1   1   0   0   Lock is acquired by a writer.
+   #8    1   1   >0  0   Lock acquired by a writer and readers are waiting;
+			 explicit hand-over to the readers is required.
+
+   WP (PTHREAD_RWLOCK_WRPHASE) is true if the lock is in a write phase, so
+   potentially acquired by a primary writer.
+   WL (PTHREAD_RWLOCK_WRLOCKED) is true if there is a primary writer (i.e.,
+   the thread that was able to set this bit from false to true).
+   R (all bits in __readers except the number of least-significant bits
+   denoted in PTHREAD_RWLOCK_READER_SHIFT) is the number of readers that have
+   or are trying to acquired the lock.  There may be more readers waiting if
+   writers are preferred and there will be no recursive readers, in which
+   case RW (PTHREAD_RWLOCK_RWAITING) is true in state #4a.
+
+   We want to block using futexes but using __readers as a futex word directly
+   is not a good solution.  First, we want to wait on different conditions
+   such as waiting for a phase change vs. waiting for the primary writer to
+   release the writer-only lock.  Second, the number of readers could change
+   frequently, which would make it likely that a writer's futex_wait fails
+   frequently too because the expected value does not match the value of
+   __readers anymore.
+   Therefore, we split out the futex words into the __wrphase_futex and
+   __writers_futex fields.  The former tracks the value of the WP bit and is
+   changed after changing WP by the thread that changes WP.  However, because
+   of the POSIX requirements regarding mutex/rwlock destruction (i.e., that
+   destroying a rwlock is allowed as soon as no thread has acquired or will
+   acquire the lock), we have to be careful and hand over lock ownership (via
+   a phase change) carefully to those threads waiting.  Specifically, we must
+   prevent a situation in which we are not quite sure whether we still have
+   to unblock another thread through a change to memory (executing a
+   futex_wake on a former futex word that is now used for something else is
+   fine).
+   The scheme we use for __wrphase_futex is that waiting threads that may
+   use the futex word to block now all have to use the futex word to block; it
+   is not allowed to take the short-cut and spin-wait on __readers because
+   then the waking thread cannot just make one final change to memory to
+   unblock all potentially waiting threads.  If, for example, a reader
+   increments R in states #7 or #8, it has to then block until __wrphase_futex
+   is 0 and it can confirm that the value of 0 was stored by the primary
+   writer; in turn, the primary writer has to change to a read phase too when
+   releasing WL (i.e., to state #2), and it must change __wrphase_futex to 0
+   as the next step.  This ensures that the waiting reader will not be able to
+   acquire, release, and then destroy the lock concurrently with the pending
+   futex unblock operations by the former primary writer.  This scheme is
+   called explicit hand-over in what follows.
+   Note that waiting threads can cancel waiting only if explicit hand-over has
+   not yet started (e.g., if __readers is still in states #7 or #8 in the
+   example above).
+
+   Writers determine the primary writer through WL.  Blocking using futexes
+   is performed using __writers_futex as a futex word; primary writers will
+   enable waiting on this futex by setting it to 1 after they acquired the WL
+   bit and will disable waiting by setting it to 0 before they release WL.
+   This leaves small windows where blocking using futexes is not possible
+   although a primary writer exists, but in turn decreases complexity of the
+   writer--writer synchronization and does not affect correctness.
+   If writers are preferred, writers can hand over WL directly to other
+   waiting writers that registered by incrementing __writers:  If the primary
+   writer can CAS __writers from a non-zero value to the same value with the
+   PTHREAD_RWLOCK_WRHANDOVER bit set, it effectively transfers WL ownership
+   to one of the registered waiting writers and does not reset WL; in turn,
+   a registered writer that can clear PTHREAD_RWLOCK_WRHANDOVER using a CAS
+   then takes over WL.  Note that registered waiting writers can cancel
+   waiting by decrementing __writers, but the last writer to unregister must
+   become the primary writer if PTHREAD_RWLOCK_WRHANDOVER is set.
+   Also note that adding another state/bit to signal potential writer--writer
+   contention (e.g., as done in the normal mutex algorithm) would not be
+   helpful because we would have to conservatively assume that there is in
+   fact no other writer, and wake up readers too.
+
+   To avoid having to call futex_wake when no thread uses __wrphase_futex or
+   __writers_futex, threads will set the PTHREAD_RWLOCK_FUTEX_USED bit in the
+   respective futex words before waiting on it (using a CAS so it will only be
+   set if in a state in which waiting would be possible).  In the case of
+   __writers_futex, we wake only one thread but several threads may share
+   PTHREAD_RWLOCK_FUTEX_USED, so we must assume that there are still others.
+   This is similar to what we do in pthread_mutex_lock.  We do not need to
+   do this for __wrphase_futex because there, we always wake all waiting
+   threads.
+
+   Blocking in the state #4a simply uses __readers as futex word.  This
+   simplifies the algorithm but suffers from some of the drawbacks discussed
+   before, though not to the same extent because R can only decrease in this
+   state, so the number of potentially failing futex_wait attempts will be
+   bounded.  All threads moving from state #4a to another state must wake
+   up threads blocked on the __readers futex.
+
+   The ordering invariants that we have to take care of in the implementation
+   are primarily those necessary for a reader--writer lock; this is rather
+   straightforward and happens during write/read phase switching (potentially
+   through explicit hand-over), and between writers through synchronization
+   involving the PTHREAD_RWLOCK_WRLOCKED or PTHREAD_RWLOCK_WRHANDOVER bits.
+   Additionally, we need to take care that modifications of __writers_futex
+   and __wrphase_futex (e.g., by otherwise unordered readers) take place in
+   the writer critical sections or read/write phases, respectively, and that
+   explicit hand-over observes stores from the previous phase.  How this is
+   done is explained in more detail in comments in the code.
+
+   Many of the accesses to the futex words just need relaxed MO.  This is
+   possible because we essentially drive both the core rwlock synchronization
+   and the futex synchronization in parallel.  For example, an unlock will
+   unlock the rwlock and take part in the futex synchronization (using
+   PTHREAD_RWLOCK_FUTEX_USED, see above); even if they are not tightly
+   ordered in some way, the futex synchronization ensures that there are no
+   lost wake-ups, and woken threads will then eventually see the most recent
+   state of the rwlock.  IOW, waiting threads will always be woken up, while
+   not being able to wait using futexes (which can happen) is harmless; in
+   turn, this means that waiting threads don't need special ordering wrt.
+   waking threads.
+
+   The futex synchronization consists of the three-state futex word:
+   (1) cannot block on it, (2) can block on it, and (3) there might be a
+   thread blocked on it (i.e., with PTHREAD_RWLOCK_FUTEX_USED set).
+   Relaxed-MO atomic read-modify-write operations are sufficient to maintain
+   this (e.g., using a CAS to go from (2) to (3) but not from (1) to (3)),
+   but we need ordering of the futex word modifications by the waking threads
+   so that they collectively make correct state changes between (1)-(3).
+   The futex-internal synchronization (i.e., the conceptual critical sections
+   around futex operations in the kernel) then ensures that even an
+   unconstrained load (i.e., relaxed MO) inside of futex_wait will not lead to
+   lost wake-ups because either the waiting thread will see the change from
+   (3) to (1) when a futex_wake came first, or this futex_wake will wake this
+   waiting thread because the waiting thread came first.
+
+
+   POSIX allows but does not require rwlock acquisitions to be a cancellation
+   point.  We do not support cancellation.
+
+   TODO We do not try to elide any read or write lock acquisitions currently.
+   While this would be possible, it is unclear whether HTM performance is
+   currently predictable enough and our runtime tuning is good enough at
+   deciding when to use elision so that enabling it would lead to consistently
+   better performance.  */
+
+
+static int
+__pthread_rwlock_get_private (pthread_rwlock_t *rwlock)
+{
+  return rwlock->__data.__shared != 0 ? FUTEX_SHARED : FUTEX_PRIVATE;
+}
+
+static __always_inline void
+__pthread_rwlock_rdunlock (pthread_rwlock_t *rwlock)
+{
+  int private = __pthread_rwlock_get_private (rwlock);
+  /* We decrease the number of readers, and if we are the last reader and
+     there is a primary writer, we start a write phase.  We use a CAS to
+     make this atomic so that it is clear whether we must hand over ownership
+     explicitly.  */
+  unsigned int r = atomic_load_relaxed (&rwlock->__data.__readers);
+  unsigned int rnew;
+  for (;;)
+    {
+      rnew = r - (1 << PTHREAD_RWLOCK_READER_SHIFT);
+      /* If we are the last reader, we also need to unblock any readers
+	 that are waiting for a writer to go first (PTHREAD_RWLOCK_RWAITING)
+	 so that they can register while the writer is active.  */
+      if ((rnew >> PTHREAD_RWLOCK_READER_SHIFT) == 0)
+	{
+	  if ((rnew & PTHREAD_RWLOCK_WRLOCKED) != 0)
+	    rnew |= PTHREAD_RWLOCK_WRPHASE;
+	  rnew &= ~(unsigned int) PTHREAD_RWLOCK_RWAITING;
+	}
+      /* We need release MO here for three reasons.  First, so that we
+	 synchronize with subsequent writers.  Second, we might have been the
+	 first reader and set __wrphase_futex to 0, so we need to synchronize
+	 with the last reader that will set it to 1 (note that we will always
+	 change __readers before the last reader, or we are the last reader).
+	 Third, a writer that takes part in explicit hand-over needs to see
+	 the first reader's store to __wrphase_futex (or a later value) if
+	 the writer observes that a write phase has been started.  */
+      if (atomic_compare_exchange_weak_release (&rwlock->__data.__readers,
+	  &r, rnew))
+	break;
+      /* TODO Back-off.  */
+    }
+  if ((rnew & PTHREAD_RWLOCK_WRPHASE) != 0)
+    {
+      /* We need to do explicit hand-over.  We need the acquire MO fence so
+	 that our modification of _wrphase_futex happens after a store by
+	 another reader that started a read phase.  Relaxed MO is sufficient
+	 for the modification of __wrphase_futex because it is just used
+	 to delay acquisition by a writer until all threads are unblocked
+	 irrespective of whether they are looking at __readers or
+	 __wrphase_futex; any other synchronizes-with relations that are
+	 necessary are established through __readers.  */
+      atomic_thread_fence_acquire ();
+      if ((atomic_exchange_relaxed (&rwlock->__data.__wrphase_futex, 1)
+	   & PTHREAD_RWLOCK_FUTEX_USED) != 0)
+	futex_wake (&rwlock->__data.__wrphase_futex, INT_MAX, private);
+    }
+  /* Also wake up waiting readers if we did reset the RWAITING flag.  */
+  if ((r & PTHREAD_RWLOCK_RWAITING) != (rnew & PTHREAD_RWLOCK_RWAITING))
+    futex_wake (&rwlock->__data.__readers, INT_MAX, private);
+}
+
+
+static __always_inline int
+__pthread_rwlock_rdlock_full (pthread_rwlock_t *rwlock,
+    const struct timespec *abstime)
+{
+  unsigned int r;
+
+  /* Make sure we are not holding the rwlock as a writer.  This is a deadlock
+     situation we recognize and report.  */
+  if (__glibc_unlikely (atomic_load_relaxed (&rwlock->__data.__cur_writer)
+      == THREAD_GETMEM (THREAD_SELF, tid)))
+    return EDEADLK;
+
+  /* If we prefer writers, recursive rdlock is disallowed, we are in a read
+     phase, and there are other readers present, we try to wait without
+     extending the read phase.  We will be unblocked by either one of the
+     other active readers, or if the writer gives up WRLOCKED (e.g., on
+     timeout).
+     If there are no other readers, we simply race with any existing primary
+     writer; it would have been a race anyway, and changing the odds slightly
+     will likely not make a big difference.  */
+  if (rwlock->__data.__flags == PTHREAD_RWLOCK_PREFER_WRITER_NONRECURSIVE_NP)
+    {
+      r = atomic_load_relaxed (&rwlock->__data.__readers);
+      while (((r & PTHREAD_RWLOCK_WRPHASE) == 0)
+	      && ((r & PTHREAD_RWLOCK_WRLOCKED) != 0)
+	      && ((r >> PTHREAD_RWLOCK_READER_SHIFT) > 0))
+	{
+	  /* TODO Spin first.  */
+	  /* Try setting the flag signaling that we are waiting without having
+	     incremented the number of readers.  Relaxed MO is fine because
+	     this is just about waiting for a state change in __readers.  */
+	  if (atomic_compare_exchange_weak_relaxed
+	      (&rwlock->__data.__readers, &r, r | PTHREAD_RWLOCK_RWAITING))
+	    {
+	      /* Wait for as long as the flag is set.  An ABA situation is
+		 harmless because the flag is just about the state of
+		 __readers, and all threads set the flag under the same
+		 conditions.  */
+	      while ((atomic_load_relaxed (&rwlock->__data.__readers)
+		  & PTHREAD_RWLOCK_RWAITING) != 0)
+		{
+		  int private = __pthread_rwlock_get_private (rwlock);
+		  int err = futex_abstimed_wait (&rwlock->__data.__readers,
+		      r, abstime, private);
+		  /* We ignore EAGAIN and EINTR.  On time-outs, we can just
+		     return because we don't need to clean up anything.  */
+		  if (err == ETIMEDOUT)
+		    return err;
+		}
+	      /* It makes sense to not break out of the outer loop here
+		 because we might be in the same situation again.  */
+	    }
+	  else
+	    {
+	      /* TODO Back-off.  */
+	    }
+	}
+    }
+  /* Register as a reader, using an add-and-fetch so that R can be used as
+     expected value for future operations.  Acquire MO so we synchronize with
+     prior writers as well as the last reader of the previous read phase (see
+     below).  */
+  r = atomic_fetch_add_acquire (&rwlock->__data.__readers,
+      (1 << PTHREAD_RWLOCK_READER_SHIFT)) + (1 << PTHREAD_RWLOCK_READER_SHIFT);
+
+  /* Check whether there is an overflow in the number of readers.  We assume
+     that the total number of threads is less than half the maximum number
+     of readers that we have bits for in __readers (i.e., with 32-bit int and
+     PTHREAD_RWLOCK_READER_SHIFT of 3, we assume there are less than
+     1 << (32-3-1) concurrent threads).
+     If there is an overflow, we use a CAS to try to decrement the number of
+     readers if there still is an overflow situation.  If so, we return
+     EAGAIN; if not, we are not a thread causing an overflow situation, and so
+     we just continue.  Using a fetch-add instead of the CAS isn't possible
+     because other readers might release the lock concurrently, which could
+     make us the last reader and thus responsible for handing ownership over
+     to writers (which requires a CAS too to make the decrement and ownership
+     transfer indivisible).  */
+  while (__glibc_unlikely (r >= PTHREAD_RWLOCK_READER_OVERFLOW))
+    {
+      /* Relaxed MO is okay because we just want to undo our registration and
+	 cannot have changed the rwlock state substantially if the CAS
+	 succeeds.  */
+      if (atomic_compare_exchange_weak_relaxed (&rwlock->__data.__readers, &r,
+	  r - (1 << PTHREAD_RWLOCK_READER_SHIFT)))
+	return EAGAIN;
+    }
+
+  /* We have registered as a reader, so if we are in a read phase, we have
+     acquired a read lock.  This is also the reader--reader fast-path.
+     Even if there is a primary writer, we just return.  If writers are to
+     be preferred and we are the only active reader, we could try to enter a
+     write phase to let the writer proceed.  This would be okay because we
+     cannot have acquired the lock previously as a reader (which could result
+     in deadlock if we would wait for the primary writer to run).  However,
+     this seems to be a corner case and handling it specially not be worth the
+     complexity.  */
+  if (__glibc_likely ((r & PTHREAD_RWLOCK_WRPHASE) == 0))
+    return 0;
+
+  /* If there is no primary writer but we are in a write phase, we can try
+     to install a read phase ourself.  */
+  while (((r & PTHREAD_RWLOCK_WRPHASE) != 0)
+      && ((r & PTHREAD_RWLOCK_WRLOCKED) == 0))
+    {
+       /* Try to enter a read phase: If the CAS below succeeds, we have
+	 ownership; if it fails, we will simply retry and reassess the
+	 situation.
+	 Acquire MO so we synchronize with prior writers.  */
+      if (atomic_compare_exchange_weak_acquire (&rwlock->__data.__readers, &r,
+	  r ^ PTHREAD_RWLOCK_WRPHASE))
+	{
+	  /* We started the read phase, so we are also responsible for
+	     updating the write-phase futex.  Relaxed MO is sufficient.
+	     Note that there can be no other reader that we have to wake
+	     because all other readers will see the read phase started by us
+	     (or they will try to start it themselves); if a writer started
+	     the read phase, we cannot have started it.  Furthermore, we
+	     cannot discard a PTHREAD_RWLOCK_FUTEX_USED flag because we will
+	     overwrite the value set by the most recent writer (or the readers
+	     before it in case of explicit hand-over) and we know that there
+	     are no waiting readers.  */
+	  atomic_store_relaxed (&rwlock->__data.__wrphase_futex, 0);
+	  return 0;
+	}
+      else
+	{
+	  /* TODO Back off before retrying.  Also see above.  */
+	}
+    }
+
+  if ((r & PTHREAD_RWLOCK_WRPHASE) != 0)
+    {
+      /* We are in a write phase, and there must be a primary writer because
+	 of the previous loop.  Block until the primary writer gives up the
+	 write phase.  This case requires explicit hand-over using
+	 __wrphase_futex.
+	 However, __wrphase_futex might not have been set to 1 yet (either
+	 because explicit hand-over to the writer is still ongoing, or because
+	 the writer has started the write phase but does not yet have updated
+	 __wrphase_futex).  The least recent value of __wrphase_futex we can
+	 read from here is the modification of the last read phase (because
+	 we synchronize with the last reader in this read phase through
+	 __readers; see the use of acquire MO on the fetch_add above).
+	 Therefore, if we observe a value of 0 for __wrphase_futex, we need
+	 to subsequently check that __readers now indicates a read phase; we
+	 need to use acquire MO for this so that if we observe a read phase,
+	 we will also see the modification of __wrphase_futex by the previous
+	 writer.  We then need to load __wrphase_futex again and continue to
+	 wait if it is not 0, so that we do not skip explicit hand-over.
+	 Relaxed MO is sufficient for the load from __wrphase_futex because
+	 we just use it as an indicator for when we can proceed; we use
+	 __readers and the acquire MO accesses to it to eventually read from
+	 the proper stores to __wrphase_futex.  */
+      unsigned int wpf;
+      bool ready = false;
+      for (;;)
+	{
+	  while (((wpf = atomic_load_relaxed (&rwlock->__data.__wrphase_futex))
+	      | PTHREAD_RWLOCK_FUTEX_USED) == (1 | PTHREAD_RWLOCK_FUTEX_USED))
+	    {
+	      int private = __pthread_rwlock_get_private (rwlock);
+	      if (((wpf & PTHREAD_RWLOCK_FUTEX_USED) == 0)
+		  && !atomic_compare_exchange_weak_relaxed
+		      (&rwlock->__data.__wrphase_futex,
+		       &wpf, wpf | PTHREAD_RWLOCK_FUTEX_USED))
+		continue;
+	      int err = futex_abstimed_wait (&rwlock->__data.__wrphase_futex,
+		  1 | PTHREAD_RWLOCK_FUTEX_USED, abstime, private);
+	      if (err == ETIMEDOUT)
+		{
+		  /* If we timed out, we need to unregister.  If no read phase
+		     has been installed while we waited, we can just decrement
+		     the number of readers.  Otherwise, we just acquire the
+		     lock, which is allowed because we give no precise timing
+		     guarantees, and because the timeout is only required to
+		     be in effect if we would have had to wait for other
+		     threads (e.g., if futex_wait would time-out immediately
+		     because the given absolute time is in the past).  */
+		  r = atomic_load_relaxed (&rwlock->__data.__readers);
+		  while ((r & PTHREAD_RWLOCK_WRPHASE) != 0)
+		    {
+		      /* We don't need to make anything else visible to
+			 others besides unregistering, so relaxed MO is
+			 sufficient.  */
+		      if (atomic_compare_exchange_weak_relaxed
+			  (&rwlock->__data.__readers, &r,
+			   r - (1 << PTHREAD_RWLOCK_READER_SHIFT)))
+			return ETIMEDOUT;
+		      /* TODO Back-off.  */
+		    }
+		  /* Use the acquire MO fence to mirror the steps taken in the
+		     non-timeout case.  Note that the read can happen both
+		     in the atomic_load above as well as in the failure case
+		     of the CAS operation.  */
+		  atomic_thread_fence_acquire ();
+		  /* We still need to wait for explicit hand-over, but we must
+		     not use futex_wait anymore because we would just time out
+		     in this case and thus make the spin-waiting we need
+		     unnecessarily expensive.  */
+		  while ((atomic_load_relaxed (&rwlock->__data.__wrphase_futex)
+		      | PTHREAD_RWLOCK_FUTEX_USED)
+		      == (1 | PTHREAD_RWLOCK_FUTEX_USED))
+		    {
+		      /* TODO Back-off?  */
+		    }
+		  ready = true;
+		  break;
+		}
+	      /* If we got interrupted (EINTR) or the futex word does not have the
+		 expected value (EAGAIN), retry.  */
+	    }
+	  if (ready)
+	    /* See below.  */
+	    break;
+	  /* We need acquire MO here so that we synchronize with the lock
+	     release of the writer, and so that we observe a recent value of
+	     __wrphase_futex (see below).  */
+	  if ((atomic_load_acquire (&rwlock->__data.__readers)
+	      & PTHREAD_RWLOCK_WRPHASE) == 0)
+	    /* We are in a read phase now, so the least recent modification of
+	       __wrphase_futex we can read from is the store by the writer
+	       with value 1.  Thus, only now we can assume that if we observe
+	       a value of 0, explicit hand-over is finished. Retry the loop
+	       above one more time.  */
+	    ready = true;
+	}
+    }
+
+  return 0;
+}
+
+
+static __always_inline void
+__pthread_rwlock_wrunlock (pthread_rwlock_t *rwlock)
+{
+  int private = __pthread_rwlock_get_private (rwlock);
+
+  atomic_store_relaxed (&rwlock->__data.__cur_writer, 0);
+  /* Disable waiting by writers.  We will wake up after we decided how to
+     proceed.  */
+  bool wake_writers = ((atomic_exchange_relaxed
+      (&rwlock->__data.__writers_futex, 0) & PTHREAD_RWLOCK_FUTEX_USED) != 0);
+
+  if (rwlock->__data.__flags != PTHREAD_RWLOCK_PREFER_READER_NP)
+    {
+      /* First, try to hand over to another writer.  */
+      unsigned int w = atomic_load_relaxed (&rwlock->__data.__writers);
+      while (w != 0)
+	{
+	  /* Release MO so that another writer that gets WRLOCKED from us will
+	     synchronize with us and thus can take over our view of
+	     __readers (including, for example, whether we are in a write
+	     phase or not).  */
+	  if (atomic_compare_exchange_weak_release (&rwlock->__data.__writers,
+	      &w, w | PTHREAD_RWLOCK_WRHANDOVER))
+	    /* Another writer will take over.  */
+	    goto done;
+	  /* TODO Back-off.  */
+	}
+    }
+
+  /* We have done everything we needed to do to prefer writers, so now we
+     either hand over explicitly to readers if there are any, or we simply
+     stay in a write phase.  See pthread_rwlock_rdunlock for more details.  */
+  unsigned int r = atomic_load_relaxed (&rwlock->__data.__readers);
+  /* Release MO so that subsequent readers or writers synchronize with us.  */
+  while (!atomic_compare_exchange_weak_release
+      (&rwlock->__data.__readers, &r, (r ^ PTHREAD_RWLOCK_WRLOCKED)
+	  ^ ((r >> PTHREAD_RWLOCK_READER_SHIFT) == 0 ? 0
+	      : PTHREAD_RWLOCK_WRPHASE)))
+    {
+      /* TODO Back-off.  */
+    }
+  if ((r >> PTHREAD_RWLOCK_READER_SHIFT) != 0)
+    {
+      /* We must hand over explicitly through __wrphase_futex.  Relaxed MO is
+	 sufficient because it is just used to delay acquisition by a writer;
+	 any other synchronizes-with relations that are necessary are
+	 established through __readers.  */
+      if ((atomic_exchange_relaxed (&rwlock->__data.__wrphase_futex, 0)
+	   & PTHREAD_RWLOCK_FUTEX_USED) != 0)
+	futex_wake (&rwlock->__data.__wrphase_futex, INT_MAX, private);
+    }
+
+ done:
+  /* We released WRLOCKED in some way, so wake a writer.  */
+  if (wake_writers)
+    futex_wake (&rwlock->__data.__writers_futex, 1, private);
+}
+
+
+static __always_inline int
+__pthread_rwlock_wrlock_full (pthread_rwlock_t *rwlock,
+    const struct timespec *abstime)
+{
+  /* Make sure we are not holding the rwlock as a writer.  This is a deadlock
+     situation we recognize and report.  */
+  if (__glibc_unlikely (atomic_load_relaxed (&rwlock->__data.__cur_writer)
+      == THREAD_GETMEM (THREAD_SELF, tid)))
+    return EDEADLK;
+
+  /* First we try to acquire the role of primary writer by setting WRLOCKED;
+     if it was set before, there already is a primary writer.  Acquire MO so
+     that we synchronize with previous primary writers.
+
+     We do not try to change to a write phase right away using a fetch_or
+     because we would have to reset it again and wake readers if there are
+     readers present (some readers could try to acquire the lock more than
+     once, so setting a write phase in the middle of this could cause
+     deadlock).  Changing to a write phase eagerly would only speed up the
+     transition from a read phase to a write phase in the uncontended case,
+     but it would slow down the contended case if readers are preferred (which
+     is the default).
+     We could try to CAS from a state with no readers to a write phase, but
+     this could be less scalable if readers arrive and leave frequently.  */
+  bool may_share_futex_used_flag = false;
+  unsigned int r = atomic_fetch_or_acquire (&rwlock->__data.__readers,
+      PTHREAD_RWLOCK_WRLOCKED);
+  if (__glibc_unlikely ((r & PTHREAD_RWLOCK_WRLOCKED) != 0))
+    {
+      /* There is another primary writer.  */
+      bool prefer_writer =
+	  (rwlock->__data.__flags != PTHREAD_RWLOCK_PREFER_READER_NP);
+      if (prefer_writer)
+	{
+	  /* We register as a waiting writer, so that we can make use of
+	     writer--writer hand-over.  Relaxed MO is fine because we just
+	     want to register.  We assume that the maximum number of threads
+	     is less than the capacity in __writers.  */
+	  atomic_fetch_add_relaxed (&rwlock->__data.__writers, 1);
+	}
+      for (;;)
+	{
+	  /* TODO Spin until WRLOCKED is 0 before trying the CAS below.
+	     But pay attention to not delay trying writer--writer hand-over
+	     for too long (which we must try eventually anyway).  */
+	  if ((r & PTHREAD_RWLOCK_WRLOCKED) == 0)
+	    {
+	      /* Try to become the primary writer or retry.  Acquire MO as in
+		 the fetch_or above.  */
+	      if (atomic_compare_exchange_weak_acquire
+		  (&rwlock->__data.__readers, &r,
+		      r | PTHREAD_RWLOCK_WRLOCKED))
+		{
+		  if (prefer_writer)
+		    {
+		      /* Unregister as a waiting writer.  Note that because we
+			 acquired WRLOCKED, WRHANDOVER will not be set.
+			 Acquire MO on the CAS above ensures that
+			 unregistering happens after the previous writer;
+			 this sorts the accesses to __writers by all
+			 primary writers in a useful way (e.g., any other
+			 primary writer acquiring after us or getting it from
+			 us through WRHANDOVER will see both our changes to
+			 __writers).
+			 ??? Perhaps this is not strictly necessary for
+			 reasons we do not yet know of.  */
+		      atomic_fetch_add_relaxed (&rwlock->__data.__writers,
+			  -1);
+		    }
+		  break;
+		}
+	      /* Retry if the CAS fails (r will have been updated).  */
+	      continue;
+	    }
+	  /* If writer--writer hand-over is available, try to become the
+	     primary writer this way by grabbing the WRHANDOVER token.  If we
+	     succeed, we own WRLOCKED.  */
+	  if (prefer_writer)
+	    {
+	      unsigned int w = atomic_load_relaxed
+		  (&rwlock->__data.__writers);
+	      if ((w & PTHREAD_RWLOCK_WRHANDOVER) != 0)
+		{
+		  /* Acquire MO is required here so that we synchronize with
+		     the writer that handed over WRLOCKED.  We also need this
+		     for the reload of __readers below because our view of
+		     __readers must be at least as recent as the view of the
+		     writer that handed over WRLOCKED; we must avoid an ABA
+		     through WRHANDOVER, which could, for example, lead to us
+		     assuming we are still in a write phase when in fact we
+		     are not.  */
+		  if (atomic_compare_exchange_weak_acquire
+		      (&rwlock->__data.__writers,
+		       &w, (w - PTHREAD_RWLOCK_WRHANDOVER - 1)))
+		    {
+		      /* Reload so our view is consistent with the view of
+			 the previous owner of WRLOCKED.  See above.  */
+		      r = atomic_load_relaxed (&rwlock->__data.__readers);
+		      break;
+		    }
+		  /* We do not need to reload __readers here.  We should try
+		     to perform writer--writer hand-over if possible; if it
+		     is not possible anymore, we will reload __readers
+		     elsewhere in this loop.  */
+		  continue;
+		}
+	    }
+	  /* We did not acquire WRLOCKED nor were able to use writer--writer
+	     hand-over, so we block on __writers_futex.  */
+	  int private = __pthread_rwlock_get_private (rwlock);
+	  unsigned int wf = atomic_load_relaxed
+	      (&rwlock->__data.__writers_futex);
+	  if (((wf & ~(unsigned int) PTHREAD_RWLOCK_FUTEX_USED) != 1)
+	      || ((wf != (1 | PTHREAD_RWLOCK_FUTEX_USED))
+		  && !atomic_compare_exchange_weak_relaxed
+		      (&rwlock->__data.__writers_futex, &wf,
+		       1 | PTHREAD_RWLOCK_FUTEX_USED)))
+	    {
+	      /* If we cannot block on __writers_futex because there is no
+		 primary writer, or we cannot set PTHREAD_RWLOCK_FUTEX_USED,
+		 we retry.  We must reload __readers here in case we cannot
+		 block on __writers_futex so that we can become the primary
+		 writer and are not stuck in a loop that just continuously
+		 fails to block on __writers_futex.  */
+	      r = atomic_load_relaxed (&rwlock->__data.__readers);
+	      continue;
+	    }
+	  /* We set the flag that signals that the futex is used, or we could
+	     have set it if we had been faster than other waiters.  As a
+	     result, we may share the flag with an unknown number of other
+	     writers.  Therefore, we must keep this flag set when we acquire
+	     the lock.  We do not need to do this when we do not reach this
+	     point here because then we are not part of the group that may
+	     share the flag, and another writer will wake one of the writers
+	     in this group.  */
+	  may_share_futex_used_flag = true;
+	  int err = futex_abstimed_wait (&rwlock->__data.__writers_futex,
+	      1 | PTHREAD_RWLOCK_FUTEX_USED, abstime, private);
+	  if (err == ETIMEDOUT)
+	    {
+	      if (prefer_writer)
+		{
+		  /* We need to unregister as a waiting writer.  If we are the
+		     last writer and writer--writer hand-over is available,
+		     we must make use of it because nobody else will reset
+		     WRLOCKED otherwise.  (If we use it, we simply pretend
+		     that this happened before the timeout; see
+		     pthread_rwlock_rdlock_full for the full reasoning.)
+		     Also see the similar code above.  */
+		  unsigned int w = atomic_load_relaxed
+		      (&rwlock->__data.__writers);
+		  while (!atomic_compare_exchange_weak_acquire
+		      (&rwlock->__data.__writers, &w,
+			  (w == PTHREAD_RWLOCK_WRHANDOVER + 1 ? 0 : w - 1)))
+		    {
+		      /* TODO Back-off.  */
+		    }
+		  if (w == PTHREAD_RWLOCK_WRHANDOVER + 1)
+		    {
+		      /* We must continue as primary writer.  See above.  */
+		      r = atomic_load_relaxed (&rwlock->__data.__readers);
+		      break;
+		    }
+		}
+	      /* We cleaned up and cannot have stolen another waiting writer's
+		 futex wake-up, so just return.  */
+	      return ETIMEDOUT;
+	    }
+	  /* If we got interrupted (EINTR) or the futex word does not have the
+	     expected value (EAGAIN), retry after reloading __readers.  */
+	  r = atomic_load_relaxed (&rwlock->__data.__readers);
+	}
+      /* Our snapshot of __readers is up-to-date at this point because we
+	 either set WRLOCKED using a CAS or were handed over WRLOCKED from
+	 another writer whose snapshot of __readers we inherit.  */
+    }
+
+  /* If we are in a read phase and there are no readers, try to start a write
+     phase.  */
+  while (((r & PTHREAD_RWLOCK_WRPHASE) == 0)
+      && ((r >> PTHREAD_RWLOCK_READER_SHIFT) == 0))
+    {
+      /* Acquire MO so that we synchronize with prior writers and do
+	 not interfere with their updates to __writers_futex, as well
+	 as regarding prior readers and their updates to __wrphase_futex,
+	 respectively.  */
+      if (atomic_compare_exchange_weak_acquire (&rwlock->__data.__readers,
+	  &r, r | PTHREAD_RWLOCK_WRPHASE))
+	{
+	  /* We have started a write phase, so need to enable readers to wait.
+	     See the similar case in__pthread_rwlock_rdlock_full.  */
+	  atomic_store_relaxed (&rwlock->__data.__wrphase_futex, 1);
+	  /* Make sure we fall through to the end of the function.  */
+	  r |= PTHREAD_RWLOCK_WRPHASE;
+	  break;
+	}
+      /* TODO Back-off.  */
+    }
+
+  /* We are the primary writer; enable blocking on __writers_futex.  Relaxed
+     MO is sufficient for futex words; acquire MO on the previous
+     modifications of __readers ensures that this store happens after the
+     store of value 0 by the previous primary writer.  */
+  atomic_store_relaxed (&rwlock->__data.__writers_futex,
+      1 | (may_share_futex_used_flag ? PTHREAD_RWLOCK_FUTEX_USED : 0));
+
+  if (__glibc_unlikely ((r & PTHREAD_RWLOCK_WRPHASE) == 0))
+    {
+      /* We are not in a read phase and there are readers (because of the
+	 previous loop).  Thus, we have to wait for explicit hand-over from
+	 one of these readers.
+	 We basically do the same steps as for the similar case in
+	 __pthread_rwlock_rdlock_full, except that we additionally might try
+	 to directly hand over to another writer and need to wake up
+	 other writers or waiting readers (i.e., PTHREAD_RWLOCK_RWAITING).  */
+      unsigned int wpf;
+      bool ready = false;
+      for (;;)
+	{
+	  while (((wpf = atomic_load_relaxed (&rwlock->__data.__wrphase_futex))
+	      | PTHREAD_RWLOCK_FUTEX_USED) == PTHREAD_RWLOCK_FUTEX_USED)
+	    {
+	      int private = __pthread_rwlock_get_private (rwlock);
+	      if (((wpf & PTHREAD_RWLOCK_FUTEX_USED) == 0)
+		  && !atomic_compare_exchange_weak_relaxed
+		      (&rwlock->__data.__wrphase_futex, &wpf,
+		       PTHREAD_RWLOCK_FUTEX_USED))
+		continue;
+	      int err = futex_abstimed_wait (&rwlock->__data.__wrphase_futex,
+		  PTHREAD_RWLOCK_FUTEX_USED, abstime, private);
+	      if (err == ETIMEDOUT)
+		{
+		  if (rwlock->__data.__flags
+		      != PTHREAD_RWLOCK_PREFER_READER_NP)
+		    {
+		      /* We try writer--writer hand-over.  */
+		      unsigned int w = atomic_load_relaxed
+			  (&rwlock->__data.__writers);
+		      if (w != 0)
+			{
+			  /* We are about to hand over WRLOCKED, so we must
+			     release __writers_futex too; otherwise, we'd have
+			     a pending store, which could at least prevent
+			     other threads from waiting using the futex
+			     because it could interleave with the stores
+			     by subsequent writers.  In turn, this means that
+			     we have to clean up when we do not hand over
+			     WRLOCKED.
+			     Release MO so that another writer that gets
+			     WRLOCKED from us can take over our view of
+			     __readers.  */
+			  unsigned int wf = atomic_exchange_relaxed
+			      (&rwlock->__data.__writers_futex, 0);
+			  while (w != 0)
+			    {
+			      if (atomic_compare_exchange_weak_release
+				  (&rwlock->__data.__writers, &w,
+				      w | PTHREAD_RWLOCK_WRHANDOVER))
+				{
+				  /* Wake other writers.  */
+				  if ((wf & PTHREAD_RWLOCK_FUTEX_USED) != 0)
+				    futex_wake
+					(&rwlock->__data.__writers_futex, 1,
+					 private);
+				  return ETIMEDOUT;
+				}
+			      /* TODO Back-off.  */
+			    }
+			  /* We still own WRLOCKED and someone else might set
+			     a write phase concurrently, so enable waiting
+			     again.  Make sure we don't loose the flag that
+			     signals whether there are threads waiting on
+			     this futex.  */
+			  atomic_store_relaxed
+			      (&rwlock->__data.__writers_futex, wf);
+			}
+		    }
+		  /* If we timed out and we are not in a write phase, we can
+		     just stop being a primary writer.  Otherwise, we just
+		     acquire the lock.  */
+		  r = atomic_load_relaxed (&rwlock->__data.__readers);
+		  if ((r & PTHREAD_RWLOCK_WRPHASE) == 0)
+		    {
+		      /* We are about to release WRLOCKED, so we must release
+			 __writers_futex too; see the handling of
+			 writer--writer hand-over above.  */
+		      unsigned int wf = atomic_exchange_relaxed
+			  (&rwlock->__data.__writers_futex, 0);
+		      while ((r & PTHREAD_RWLOCK_WRPHASE) == 0)
+			{
+			  /* While we don't need to make anything from a
+			     caller's critical section visible to other
+			     threads, we need to ensure that our changes to
+			     __writers_futex are properly ordered.
+			     Therefore, use release MO to synchronize with
+			     subsequent primary writers.  Also wake up any
+			     waiting readers as they are waiting because of
+			     us.  */
+			  if (atomic_compare_exchange_weak_release
+			      (&rwlock->__data.__readers, &r,
+			       (r ^ PTHREAD_RWLOCK_WRLOCKED)
+			       & ~(unsigned int) PTHREAD_RWLOCK_RWAITING))
+			    {
+			      /* Wake other writers.  */
+			      if ((wf & PTHREAD_RWLOCK_FUTEX_USED) != 0)
+				futex_wake (&rwlock->__data.__writers_futex,
+				    1, private);
+			      /* Wake waiting readers.  */
+			      if ((r & PTHREAD_RWLOCK_RWAITING) != 0)
+				futex_wake (&rwlock->__data.__readers,
+				    INT_MAX, private);
+			      return ETIMEDOUT;
+			    }
+			}
+		      /* We still own WRLOCKED and someone else might set a
+			 write phase concurrently, so enable waiting again.
+			 Make sure we don't loose the flag that signals
+			 whether there are threads waiting on this futex.  */
+		      atomic_store_relaxed (&rwlock->__data.__writers_futex,
+			  wf);
+		    }
+		  /* Use the acquire MO fence to mirror the steps taken in the
+		     non-timeout case.  Note that the read can happen both
+		     in the atomic_load above as well as in the failure case
+		     of the CAS operation.  */
+		  atomic_thread_fence_acquire ();
+		  /* We still need to wait for explicit hand-over, but we must
+		     not use futex_wait anymore.  */
+		  while ((atomic_load_relaxed
+		      (&rwlock->__data.__wrphase_futex)
+		       | PTHREAD_RWLOCK_FUTEX_USED)
+		      == PTHREAD_RWLOCK_FUTEX_USED)
+		    {
+		      /* TODO Back-off.  */
+		    }
+		  ready = true;
+		  break;
+		}
+	      /* If we got interrupted (EINTR) or the futex word does not have
+		 the expected value (EAGAIN), retry.  */
+	    }
+	  /* See pthread_rwlock_rdlock_full.  */
+	  if (ready)
+	    break;
+	  if ((atomic_load_acquire (&rwlock->__data.__readers)
+	      & PTHREAD_RWLOCK_WRPHASE) != 0)
+	    ready = true;
+	}
+    }
+
+  atomic_store_relaxed (&rwlock->__data.__cur_writer,
+      THREAD_GETMEM (THREAD_SELF, tid));
+  return 0;
+}
diff --git a/nptl/pthread_rwlock_init.c b/nptl/pthread_rwlock_init.c
index 1687f22a9e..764ba110fb 100644
--- a/nptl/pthread_rwlock_init.c
+++ b/nptl/pthread_rwlock_init.c
@@ -18,7 +18,6 @@
 
 #include "pthreadP.h"
 #include <string.h>
-#include <kernel-features.h>
 
 
 static const struct pthread_rwlockattr default_rwlockattr =
@@ -28,6 +27,7 @@ static const struct pthread_rwlockattr default_rwlockattr =
   };
 
 
+/* See pthread_rwlock_common.c.  */
 int
 __pthread_rwlock_init (pthread_rwlock_t *rwlock,
 		       const pthread_rwlockattr_t *attr)
@@ -38,27 +38,10 @@ __pthread_rwlock_init (pthread_rwlock_t *rwlock,
 
   memset (rwlock, '\0', sizeof (*rwlock));
 
-  rwlock->__data.__flags
-    = iattr->lockkind == PTHREAD_RWLOCK_PREFER_WRITER_NONRECURSIVE_NP;
+  rwlock->__data.__flags = iattr->lockkind;
 
-  /* The __SHARED field is computed to minimize the work that needs to
-     be done while handling the futex.  There are two inputs: the
-     availability of private futexes and whether the rwlock is shared
-     or private.  Unfortunately the value of a private rwlock is
-     fixed: it must be zero.  The PRIVATE_FUTEX flag has the value
-     0x80 in case private futexes are available and zero otherwise.
-     This leads to the following table:
-
-		 |     pshared     |     result
-		 | shared  private | shared  private |
-     ------------+-----------------+-----------------+
-     !avail 0    |     0       0   |     0       0   |
-      avail 0x80 |  0x80       0   |     0    0x80   |
-
-     If the pshared value is in locking functions XORed with avail
-     we get the expected result.  */
-  rwlock->__data.__shared = (iattr->pshared == PTHREAD_PROCESS_PRIVATE
-			     ? 0 : FUTEX_PRIVATE_FLAG);
+  /* The value of __SHARED in a private rwlock must be zero.  */
+  rwlock->__data.__shared = (iattr->pshared != PTHREAD_PROCESS_PRIVATE);
 
   return 0;
 }
diff --git a/nptl/pthread_rwlock_rdlock.c b/nptl/pthread_rwlock_rdlock.c
index 8adefc32c0..e07581bbf5 100644
--- a/nptl/pthread_rwlock_rdlock.c
+++ b/nptl/pthread_rwlock_rdlock.c
@@ -16,165 +16,17 @@
    License along with the GNU C Library; if not, see
    <http://www.gnu.org/licenses/>.  */
 
-#include <errno.h>
-#include <sysdep.h>
-#include <lowlevellock.h>
-#include <futex-internal.h>
-#include <pthread.h>
-#include <pthreadP.h>
-#include <stap-probe.h>
-#include <elide.h>
-#include <stdbool.h>
-
-
-/* Acquire read lock for RWLOCK.  Slow path.  */
-static int __attribute__((noinline))
-__pthread_rwlock_rdlock_slow (pthread_rwlock_t *rwlock)
-{
-  int result = 0;
-  bool wake = false;
-  int futex_shared =
-      rwlock->__data.__shared == LLL_PRIVATE ? FUTEX_PRIVATE : FUTEX_SHARED;
-
-  /* Lock is taken in caller.  */
-
-  while (1)
-    {
-      /* Make sure we are not holding the rwlock as a writer.  This is
-	 a deadlock situation we recognize and report.  */
-      if (__builtin_expect (rwlock->__data.__writer
-			    == THREAD_GETMEM (THREAD_SELF, tid), 0))
-	{
-	  result = EDEADLK;
-	  break;
-	}
-
-      /* Remember that we are a reader.  */
-      if (__glibc_unlikely (++rwlock->__data.__nr_readers_queued == 0))
-	{
-	  /* Overflow on number of queued readers.  */
-	  --rwlock->__data.__nr_readers_queued;
-	  result = EAGAIN;
-	  break;
-	}
-
-      int waitval = rwlock->__data.__readers_wakeup;
-
-      /* Free the lock.  */
-      lll_unlock (rwlock->__data.__lock, rwlock->__data.__shared);
-
-      /* Wait for the writer to finish.  We do not check the return value
-	 because we decide how to continue based on the state of the rwlock.  */
-      futex_wait_simple (&rwlock->__data.__readers_wakeup, waitval,
-			 futex_shared);
-
-      /* Get the lock.  */
-      lll_lock (rwlock->__data.__lock, rwlock->__data.__shared);
-
-      --rwlock->__data.__nr_readers_queued;
-
-      /* Get the rwlock if there is no writer...  */
-      if (rwlock->__data.__writer == 0
-	  /* ...and if either no writer is waiting or we prefer readers.  */
-	  && (!rwlock->__data.__nr_writers_queued
-	      || PTHREAD_RWLOCK_PREFER_READER_P (rwlock)))
-	{
-	  /* Increment the reader counter.  Avoid overflow.  */
-	  if (__glibc_unlikely (++rwlock->__data.__nr_readers == 0))
-	    {
-	      /* Overflow on number of readers.	 */
-	      --rwlock->__data.__nr_readers;
-	      result = EAGAIN;
-	    }
-	  else
-	    {
-	      LIBC_PROBE (rdlock_acquire_read, 1, rwlock);
-	      /* See pthread_rwlock_rdlock.  */
-	      if (rwlock->__data.__nr_readers == 1
-		  && rwlock->__data.__nr_readers_queued > 0
-		  && rwlock->__data.__nr_writers_queued > 0)
-		{
-		  ++rwlock->__data.__readers_wakeup;
-		  wake = true;
-		}
-	    }
-
-	  break;
-	}
-    }
-
-  /* We are done, free the lock.  */
-  lll_unlock (rwlock->__data.__lock, rwlock->__data.__shared);
-
-  if (wake)
-    futex_wake (&rwlock->__data.__readers_wakeup, INT_MAX, futex_shared);
-
-  return result;
-}
-
-
-/* Fast path of acquiring read lock on RWLOCK.  */
+#include "pthread_rwlock_common.c"
 
+/* See pthread_rwlock_common.c.  */
 int
 __pthread_rwlock_rdlock (pthread_rwlock_t *rwlock)
 {
-  int result = 0;
-  bool wake = false;
-  int futex_shared =
-      rwlock->__data.__shared == LLL_PRIVATE ? FUTEX_PRIVATE : FUTEX_SHARED;
-
   LIBC_PROBE (rdlock_entry, 1, rwlock);
 
-  if (ELIDE_LOCK (rwlock->__data.__rwelision,
-		  rwlock->__data.__lock == 0
-		  && rwlock->__data.__writer == 0
-		  && rwlock->__data.__nr_readers == 0))
-    return 0;
-
-  /* Make sure we are alone.  */
-  lll_lock (rwlock->__data.__lock, rwlock->__data.__shared);
-
-  /* Get the rwlock if there is no writer...  */
-  if (rwlock->__data.__writer == 0
-      /* ...and if either no writer is waiting or we prefer readers.  */
-      && (!rwlock->__data.__nr_writers_queued
-	  || PTHREAD_RWLOCK_PREFER_READER_P (rwlock)))
-    {
-      /* Increment the reader counter.  Avoid overflow.  */
-      if (__glibc_unlikely (++rwlock->__data.__nr_readers == 0))
-	{
-	  /* Overflow on number of readers.	 */
-	  --rwlock->__data.__nr_readers;
-	  result = EAGAIN;
-	}
-      else
-	{
-	  LIBC_PROBE (rdlock_acquire_read, 1, rwlock);
-	  /* If we are the first reader, and there are blocked readers and
-	     writers (which we don't prefer, see above), then it can be the
-	     case that we stole the lock from a writer that was already woken
-	     to acquire it.  That means that we need to take over the writer's
-	     responsibility to wake all readers (see pthread_rwlock_unlock).
-	     Thus, wake all readers in this case.  */
-	  if (rwlock->__data.__nr_readers == 1
-	      && rwlock->__data.__nr_readers_queued > 0
-	      && rwlock->__data.__nr_writers_queued > 0)
-	    {
-	      ++rwlock->__data.__readers_wakeup;
-	      wake = true;
-	    }
-	}
-
-      /* We are done, free the lock.  */
-      lll_unlock (rwlock->__data.__lock, rwlock->__data.__shared);
-
-      if (wake)
-	futex_wake (&rwlock->__data.__readers_wakeup, INT_MAX, futex_shared);
-
-      return result;
-    }
-
-  return __pthread_rwlock_rdlock_slow (rwlock);
+  int result = __pthread_rwlock_rdlock_full (rwlock, NULL);
+  LIBC_PROBE (rdlock_acquire_read, 1, rwlock);
+  return result;
 }
 
 weak_alias (__pthread_rwlock_rdlock, pthread_rwlock_rdlock)
diff --git a/nptl/pthread_rwlock_timedrdlock.c b/nptl/pthread_rwlock_timedrdlock.c
index 003ea573c9..9f084f8c34 100644
--- a/nptl/pthread_rwlock_timedrdlock.c
+++ b/nptl/pthread_rwlock_timedrdlock.c
@@ -16,121 +16,22 @@
    License along with the GNU C Library; if not, see
    <http://www.gnu.org/licenses/>.  */
 
-#include <errno.h>
-#include <sysdep.h>
-#include <lowlevellock.h>
-#include <futex-internal.h>
-#include <pthread.h>
-#include <pthreadP.h>
-#include <sys/time.h>
-#include <stdbool.h>
+#include "pthread_rwlock_common.c"
 
-
-/* Try to acquire read lock for RWLOCK or return after specfied time.  */
+/* See pthread_rwlock_common.c.  */
 int
 pthread_rwlock_timedrdlock (pthread_rwlock_t *rwlock,
-			    const struct timespec *abstime)
+    const struct timespec *abstime)
 {
-  int result = 0;
-  bool wake = false;
-  int futex_shared =
-      rwlock->__data.__shared == LLL_PRIVATE ? FUTEX_PRIVATE : FUTEX_SHARED;
-
-  /* Make sure we are alone.  */
-  lll_lock(rwlock->__data.__lock, rwlock->__data.__shared);
-
-  while (1)
-    {
-      int err;
-
-      /* Get the rwlock if there is no writer...  */
-      if (rwlock->__data.__writer == 0
-	  /* ...and if either no writer is waiting or we prefer readers.  */
-	  && (!rwlock->__data.__nr_writers_queued
-	      || PTHREAD_RWLOCK_PREFER_READER_P (rwlock)))
-	{
-	  /* Increment the reader counter.  Avoid overflow.  */
-	  if (++rwlock->__data.__nr_readers == 0)
-	    {
-	      /* Overflow on number of readers.	 */
-	      --rwlock->__data.__nr_readers;
-	      result = EAGAIN;
-	    }
-	  else
-	    {
-	      /* See pthread_rwlock_rdlock.  */
-	      if (rwlock->__data.__nr_readers == 1
-		  && rwlock->__data.__nr_readers_queued > 0
-		  && rwlock->__data.__nr_writers_queued > 0)
-		{
-		  ++rwlock->__data.__readers_wakeup;
-		  wake = true;
-		}
-	    }
-
-	  break;
-	}
-
-      /* Make sure we are not holding the rwlock as a writer.  This is
-	 a deadlock situation we recognize and report.  */
-      if (__builtin_expect (rwlock->__data.__writer
-			    == THREAD_GETMEM (THREAD_SELF, tid), 0))
-	{
-	  result = EDEADLK;
-	  break;
-	}
-
-      /* Make sure the passed in timeout value is valid.  Ideally this
-	 test would be executed once.  But since it must not be
-	 performed if we would not block at all simply moving the test
-	 to the front is no option.  Replicating all the code is
-	 costly while this test is not.  */
-      if (__builtin_expect (abstime->tv_nsec >= 1000000000
-                            || abstime->tv_nsec < 0, 0))
-	{
-	  result = EINVAL;
-	  break;
-	}
-
-      /* Remember that we are a reader.  */
-      if (++rwlock->__data.__nr_readers_queued == 0)
-	{
-	  /* Overflow on number of queued readers.  */
-	  --rwlock->__data.__nr_readers_queued;
-	  result = EAGAIN;
-	  break;
-	}
-
-      int waitval = rwlock->__data.__readers_wakeup;
-
-      /* Free the lock.  */
-      lll_unlock (rwlock->__data.__lock, rwlock->__data.__shared);
-
-      /* Wait for the writer to finish.  We handle ETIMEDOUT below; on other
-	 return values, we decide how to continue based on the state of the
-	 rwlock.  */
-      err = futex_abstimed_wait (&rwlock->__data.__readers_wakeup, waitval,
-				 abstime, futex_shared);
-
-      /* Get the lock.  */
-      lll_lock (rwlock->__data.__lock, rwlock->__data.__shared);
-
-      --rwlock->__data.__nr_readers_queued;
-
-      /* Did the futex call time out?  */
-      if (err == ETIMEDOUT)
-	{
-	  /* Yep, report it.  */
-	  result = ETIMEDOUT;
-	  break;
-	}
-    }
-
-  /* We are done, free the lock.  */
-  lll_unlock (rwlock->__data.__lock, rwlock->__data.__shared);
-
-  if (wake)
-    futex_wake (&rwlock->__data.__readers_wakeup, INT_MAX, futex_shared);
-
-  return result;
+  /* Make sure the passed in timeout value is valid.  Note that the previous
+     implementation assumed that this check *must* not be performed if there
+     would in fact be no blocking; however, POSIX only requires that "the
+     validity of the abstime parameter need not be checked if the lock can be
+     immediately acquired" (i.e., we need not but may check it).  */
+  /* ??? Just move this to __pthread_rwlock_rdlock_full?  */
+  if (__glibc_unlikely (abstime->tv_nsec >= 1000000000
+      || abstime->tv_nsec < 0))
+    return EINVAL;
+
+  return __pthread_rwlock_rdlock_full (rwlock, abstime);
 }
diff --git a/nptl/pthread_rwlock_timedwrlock.c b/nptl/pthread_rwlock_timedwrlock.c
index 9f024be819..5626505d2c 100644
--- a/nptl/pthread_rwlock_timedwrlock.c
+++ b/nptl/pthread_rwlock_timedwrlock.c
@@ -16,121 +16,22 @@
    License along with the GNU C Library; if not, see
    <http://www.gnu.org/licenses/>.  */
 
-#include <errno.h>
-#include <sysdep.h>
-#include <lowlevellock.h>
-#include <futex-internal.h>
-#include <pthread.h>
-#include <pthreadP.h>
-#include <sys/time.h>
-#include <stdbool.h>
+#include "pthread_rwlock_common.c"
 
-
-/* Try to acquire write lock for RWLOCK or return after specfied time.	*/
+/* See pthread_rwlock_common.c.  */
 int
 pthread_rwlock_timedwrlock (pthread_rwlock_t *rwlock,
-			    const struct timespec *abstime)
+    const struct timespec *abstime)
 {
-  int result = 0;
-  bool wake_readers = false;
-  int futex_shared =
-      rwlock->__data.__shared == LLL_PRIVATE ? FUTEX_PRIVATE : FUTEX_SHARED;
-
-  /* Make sure we are alone.  */
-  lll_lock (rwlock->__data.__lock, rwlock->__data.__shared);
-
-  while (1)
-    {
-      int err;
-
-      /* Get the rwlock if there is no writer and no reader.  */
-      if (rwlock->__data.__writer == 0 && rwlock->__data.__nr_readers == 0)
-	{
-	  /* Mark self as writer.  */
-	  rwlock->__data.__writer = THREAD_GETMEM (THREAD_SELF, tid);
-	  break;
-	}
-
-      /* Make sure we are not holding the rwlock as a writer.  This is
-	 a deadlock situation we recognize and report.  */
-      if (__builtin_expect (rwlock->__data.__writer
-			    == THREAD_GETMEM (THREAD_SELF, tid), 0))
-	{
-	  result = EDEADLK;
-	  break;
-	}
-
-      /* Make sure the passed in timeout value is valid.  Ideally this
-	 test would be executed once.  But since it must not be
-	 performed if we would not block at all simply moving the test
-	 to the front is no option.  Replicating all the code is
-	 costly while this test is not.  */
-      if (__builtin_expect (abstime->tv_nsec >= 1000000000
-                            || abstime->tv_nsec < 0, 0))
-	{
-	  result = EINVAL;
-	  break;
-	}
-
-      /* Remember that we are a writer.  */
-      if (++rwlock->__data.__nr_writers_queued == 0)
-	{
-	  /* Overflow on number of queued writers.  */
-	  --rwlock->__data.__nr_writers_queued;
-	  result = EAGAIN;
-	  break;
-	}
-
-      int waitval = rwlock->__data.__writer_wakeup;
-
-      /* Free the lock.  */
-      lll_unlock (rwlock->__data.__lock, rwlock->__data.__shared);
-
-      /* Wait for the writer or reader(s) to finish.  We handle ETIMEDOUT
-	 below; on other return values, we decide how to continue based on
-	 the state of the rwlock.  */
-      err = futex_abstimed_wait (&rwlock->__data.__writer_wakeup, waitval,
-				 abstime, futex_shared);
-
-      /* Get the lock.  */
-      lll_lock (rwlock->__data.__lock, rwlock->__data.__shared);
-
-      /* To start over again, remove the thread from the writer list.  */
-      --rwlock->__data.__nr_writers_queued;
-
-      /* Did the futex call time out?  */
-      if (err == ETIMEDOUT)
-	{
-	  result = ETIMEDOUT;
-	  /* If we prefer writers, it can have happened that readers blocked
-	     for us to acquire the lock first.  If we have timed out, we need
-	     to wake such readers if there are any, and if there is no writer
-	     currently (otherwise, the writer will take care of wake-up).
-	     Likewise, even if we prefer readers, we can be responsible for
-	     wake-up (see pthread_rwlock_unlock) if no reader or writer has
-	     acquired the lock.  We have timed out and thus not consumed a
-	     futex wake-up; therefore, if there is no other blocked writer
-	     that would consume the wake-up and thus take over responsibility,
-	     we need to wake blocked readers.  */
-	  if ((!PTHREAD_RWLOCK_PREFER_READER_P (rwlock)
-	       || ((rwlock->__data.__nr_readers == 0)
-		   && (rwlock->__data.__nr_writers_queued == 0)))
-	      && (rwlock->__data.__nr_readers_queued > 0)
-	      && (rwlock->__data.__writer == 0))
-	    {
-	      ++rwlock->__data.__readers_wakeup;
-	      wake_readers = true;
-	    }
-	  break;
-	}
-    }
-
-  /* We are done, free the lock.  */
-  lll_unlock (rwlock->__data.__lock, rwlock->__data.__shared);
-
-  /* Might be required after timeouts.  */
-  if (wake_readers)
-    futex_wake (&rwlock->__data.__readers_wakeup, INT_MAX, futex_shared);
-
-  return result;
+  /* Make sure the passed in timeout value is valid.  Note that the previous
+     implementation assumed that this check *must* not be performed if there
+     would in fact be no blocking; however, POSIX only requires that "the
+     validity of the abstime parameter need not be checked if the lock can be
+     immediately acquired" (i.e., we need not but may check it).  */
+  /* ??? Just move this to __pthread_rwlock_wrlock_full?  */
+  if (__glibc_unlikely (abstime->tv_nsec >= 1000000000
+      || abstime->tv_nsec < 0))
+    return EINVAL;
+
+  return __pthread_rwlock_wrlock_full (rwlock, abstime);
 }
diff --git a/nptl/pthread_rwlock_tryrdlock.c b/nptl/pthread_rwlock_tryrdlock.c
index cdd73d25eb..6c3014ce53 100644
--- a/nptl/pthread_rwlock_tryrdlock.c
+++ b/nptl/pthread_rwlock_tryrdlock.c
@@ -18,56 +18,95 @@
 
 #include <errno.h>
 #include "pthreadP.h"
-#include <lowlevellock.h>
-#include <futex-internal.h>
-#include <elide.h>
+#include <atomic.h>
 #include <stdbool.h>
+#include "pthread_rwlock_common.c"
 
 
+/* See pthread_rwlock_common.c for an overview.  */
 int
 __pthread_rwlock_tryrdlock (pthread_rwlock_t *rwlock)
 {
-  int result = EBUSY;
-  bool wake = false;
-  int futex_shared =
-      rwlock->__data.__shared == LLL_PRIVATE ? FUTEX_PRIVATE : FUTEX_SHARED;
-
-  if (ELIDE_TRYLOCK (rwlock->__data.__rwelision,
-		     rwlock->__data.__lock == 0
-		     && rwlock->__data.__nr_readers == 0
-		     && rwlock->__data.__writer, 0))
-    return 0;
-
-  lll_lock (rwlock->__data.__lock, rwlock->__data.__shared);
-
-  if (rwlock->__data.__writer == 0
-      && (rwlock->__data.__nr_writers_queued == 0
-	  || PTHREAD_RWLOCK_PREFER_READER_P (rwlock)))
+  /* For tryrdlock, we could speculate that we will succeed and go ahead and
+     register as a reader.  However, if we misspeculate, we have to do the
+     same steps as a timed-out rdlock, which will increase contention.
+     Therefore, there is a trade-off between being able to use a combinable
+     read-modify-write operation and a CAS loop as used below; we pick the
+     latter because it simplifies the code, and should perform better when
+     tryrdlock is used in cases where writers are infrequent.
+     Because POSIX does not require a failed trylock to "synchronize memory",
+     relaxed MO is sufficient here and on the failure path of the CAS
+     below.  */
+  unsigned int r = atomic_load_relaxed (&rwlock->__data.__readers);
+  unsigned int rnew;
+  do
     {
-      if (__glibc_unlikely (++rwlock->__data.__nr_readers == 0))
+      if ((r & PTHREAD_RWLOCK_WRPHASE) == 0)
 	{
-	  --rwlock->__data.__nr_readers;
-	  result = EAGAIN;
+	  /* If we are in a read phase, try to acquire unless there is a
+	     primary writer and we prefer writers and there will be no
+	     recursive read locks.  */
+	  if (((r & PTHREAD_RWLOCK_WRLOCKED) != 0)
+	      && (rwlock->__data.__flags
+		  == PTHREAD_RWLOCK_PREFER_WRITER_NONRECURSIVE_NP))
+	    return EBUSY;
+	  rnew = r + (1 << PTHREAD_RWLOCK_READER_SHIFT);
 	}
       else
 	{
-	  result = 0;
-	  /* See pthread_rwlock_rdlock.  */
-	  if (rwlock->__data.__nr_readers == 1
-	      && rwlock->__data.__nr_readers_queued > 0
-	      && rwlock->__data.__nr_writers_queued > 0)
+	  /* If there is a writer that has acquired the lock and we are in
+	     a write phase, fail.  */
+	  if ((r & PTHREAD_RWLOCK_WRLOCKED) != 0)
+	    return EBUSY;
+	  else
 	    {
-	      ++rwlock->__data.__readers_wakeup;
-	      wake = true;
+	      /* If we do not care about potentially waiting writers, just
+		 try to acquire.  */
+	      rnew = (r + (1 << PTHREAD_RWLOCK_READER_SHIFT))
+		  ^ PTHREAD_RWLOCK_WRPHASE;
 	    }
 	}
+      /* If we could have caused an overflow or take effect during an
+	 overflow, we just can / need to return EAGAIN.  There is no need to
+	 have actually modified the number of readers because we could have
+	 done that and cleaned up immediately.  */
+      if (rnew >= PTHREAD_RWLOCK_READER_OVERFLOW)
+	return EAGAIN;
+    }
+  /* If the CAS fails, we retry; this prevents that tryrdlock fails spuriously
+     (i.e., fails to acquire the lock although there is no writer), which is
+     fine for C++14 but not currently allowed by POSIX.
+     However, because tryrdlock must not appear to block, we should avoid
+     starving this CAS loop due to constant changes to __readers:
+     While normal rdlock readers that won't be able to acquire will just block
+     (and we expect timeouts on timedrdlock to be longer than one retry of the
+     CAS loop), we can have concurrently failing tryrdlock calls due to
+     readers or writers that acquire and release in the meantime.  Using
+     randomized exponential back-off to make a live-lock unlikely should be
+     sufficient.
+     TODO Back-off.
+     Acquire MO so we synchronize with prior writers.  */
+  while (!atomic_compare_exchange_weak_acquire (&rwlock->__data.__readers,
+      &r, rnew));
+
+  if ((r & PTHREAD_RWLOCK_WRPHASE) != 0)
+    {
+      /* Same as in __pthread_rwlock_rdlock_full:
+	 We started the read phase, so we are also responsible for
+	 updating the write-phase futex.  Relaxed MO is sufficient.
+	 Note that there can be no other reader that we have to wake
+	 because all other readers will see the read phase started by us
+	 (or they will try to start it themselves); if a writer started
+	 the read phase, we cannot have started it.  Furthermore, we
+	 cannot discard a PTHREAD_RWLOCK_FUTEX_USED flag because we will
+	 overwrite the value set by the most recent writer (or the readers
+	 before it in case of explicit hand-over) and we know that there
+	 are no waiting readers.  */
+      atomic_store_relaxed (&rwlock->__data.__wrphase_futex, 0);
     }
 
-  lll_unlock (rwlock->__data.__lock, rwlock->__data.__shared);
+  return 0;
 
-  if (wake)
-    futex_wake (&rwlock->__data.__readers_wakeup, INT_MAX, futex_shared);
 
-  return result;
 }
 strong_alias (__pthread_rwlock_tryrdlock, pthread_rwlock_tryrdlock)
diff --git a/nptl/pthread_rwlock_trywrlock.c b/nptl/pthread_rwlock_trywrlock.c
index 251ece133f..0d9ccaf79c 100644
--- a/nptl/pthread_rwlock_trywrlock.c
+++ b/nptl/pthread_rwlock_trywrlock.c
@@ -18,31 +18,44 @@
 
 #include <errno.h>
 #include "pthreadP.h"
-#include <lowlevellock.h>
-#include <elide.h>
-
+#include <atomic.h>
 
+/* See pthread_rwlock_common.c for an overview.  */
 int
 __pthread_rwlock_trywrlock (pthread_rwlock_t *rwlock)
 {
-  int result = EBUSY;
-
-  if (ELIDE_TRYLOCK (rwlock->__data.__rwelision,
-		     rwlock->__data.__lock == 0
-		     && rwlock->__data.__nr_readers == 0
-		     && rwlock->__data.__writer, 1))
-    return 0;
-
-  lll_lock (rwlock->__data.__lock, rwlock->__data.__shared);
-
-  if (rwlock->__data.__writer == 0 && rwlock->__data.__nr_readers == 0)
+  /* When in a trywrlock, we can acquire the write lock if it is in states
+     #1 (idle and read phase) and #5 (idle and write phase), and also in #6
+     (readers waiting, write phase) if we prefer writers.
+     If we observe any other state, we are allowed to fail and do not need to
+     "synchronize memory" as specified by POSIX (hence relaxed MO is
+     sufficient for the first load and the CAS failure path).
+     We face a similar issue as in tryrdlock in that we need to both avoid
+     live-locks / starvation and must not fail spuriously (see there for
+     further comments) -- and thus must loop until we get a definitive
+     observation or state change.  */
+  unsigned int r = atomic_load_relaxed (&rwlock->__data.__readers);
+  bool prefer_writer =
+      (rwlock->__data.__flags != PTHREAD_RWLOCK_PREFER_READER_NP);
+  while (((r & PTHREAD_RWLOCK_WRLOCKED) == 0)
+      && (((r >> PTHREAD_RWLOCK_READER_SHIFT) == 0)
+	  || (prefer_writer && ((r & PTHREAD_RWLOCK_WRPHASE) != 0))))
     {
-      rwlock->__data.__writer = THREAD_GETMEM (THREAD_SELF, tid);
-      result = 0;
+      /* Try to transition to states #7 or #8 (i.e., acquire the lock).  */
+      if (atomic_compare_exchange_weak_acquire (
+	  &rwlock->__data.__readers, &r,
+	  r | PTHREAD_RWLOCK_WRPHASE | PTHREAD_RWLOCK_WRLOCKED))
+	{
+	  atomic_store_relaxed (&rwlock->__data.__writers_futex, 1);
+	  atomic_store_relaxed (&rwlock->__data.__wrphase_futex, 1);
+	  atomic_store_relaxed (&rwlock->__data.__cur_writer,
+	      THREAD_GETMEM (THREAD_SELF, tid));
+	  return 0;
+	}
+      /* TODO Back-off.  */
+      /* See above.  */
     }
-
-  lll_unlock (rwlock->__data.__lock, rwlock->__data.__shared);
-
-  return result;
+  return EBUSY;
 }
+
 strong_alias (__pthread_rwlock_trywrlock, pthread_rwlock_trywrlock)
diff --git a/nptl/pthread_rwlock_unlock.c b/nptl/pthread_rwlock_unlock.c
index 320837d5af..ef46e88263 100644
--- a/nptl/pthread_rwlock_unlock.c
+++ b/nptl/pthread_rwlock_unlock.c
@@ -18,60 +18,29 @@
 
 #include <errno.h>
 #include <sysdep.h>
-#include <lowlevellock.h>
 #include <futex-internal.h>
 #include <pthread.h>
 #include <pthreadP.h>
 #include <stap-probe.h>
-#include <elide.h>
 
+#include "pthread_rwlock_common.c"
 
-/* Unlock RWLOCK.  */
+/* See pthread_rwlock_common.c for an overview.  */
 int
 __pthread_rwlock_unlock (pthread_rwlock_t *rwlock)
 {
-  int futex_shared =
-      rwlock->__data.__shared == LLL_PRIVATE ? FUTEX_PRIVATE : FUTEX_SHARED;
-
   LIBC_PROBE (rwlock_unlock, 1, rwlock);
 
-  /* Trying to elide an unlocked lock may crash the process.  This
-     is expected and is compatible with POSIX.1-2008: "results are
-     undefined if the read-write lock rwlock is not held by the
-     calling thread".  */
-  if (ELIDE_UNLOCK (rwlock->__data.__writer == 0
-		    && rwlock->__data.__nr_readers == 0))
-    return 0;
-
-  lll_lock (rwlock->__data.__lock, rwlock->__data.__shared);
-  if (rwlock->__data.__writer)
-    rwlock->__data.__writer = 0;
+  /* We distinguish between having acquired a read vs. a write lock by looking
+     at the writer TID.  If it's equal to our TID, we must be the writer
+     because nobody else can have stored this value.  Also, if we are a
+     reader, we will read from the wrunlock store with value 0 by the most
+     recent writer because that writer happens-before us.  */
+  if (atomic_load_relaxed (&rwlock->__data.__cur_writer)
+      == THREAD_GETMEM (THREAD_SELF, tid))
+      __pthread_rwlock_wrunlock (rwlock);
   else
-    --rwlock->__data.__nr_readers;
-  /* If there are still readers present, we do not yet need to wake writers
-     nor are responsible to wake any readers.  */
-  if (rwlock->__data.__nr_readers == 0)
-    {
-      /* Note that if there is a blocked writer, we effectively make it
-	 responsible for waking any readers because we don't wake readers in
-	 this case.  */
-      if (rwlock->__data.__nr_writers_queued)
-	{
-	  ++rwlock->__data.__writer_wakeup;
-	  lll_unlock (rwlock->__data.__lock, rwlock->__data.__shared);
-	  futex_wake (&rwlock->__data.__writer_wakeup, 1, futex_shared);
-	  return 0;
-	}
-      else if (rwlock->__data.__nr_readers_queued)
-	{
-	  ++rwlock->__data.__readers_wakeup;
-	  lll_unlock (rwlock->__data.__lock, rwlock->__data.__shared);
-	  futex_wake (&rwlock->__data.__readers_wakeup, INT_MAX,
-		      futex_shared);
-	  return 0;
-	}
-    }
-  lll_unlock (rwlock->__data.__lock, rwlock->__data.__shared);
+    __pthread_rwlock_rdunlock (rwlock);
   return 0;
 }
 
diff --git a/nptl/pthread_rwlock_wrlock.c b/nptl/pthread_rwlock_wrlock.c
index 461ffdc06c..335fcd18cc 100644
--- a/nptl/pthread_rwlock_wrlock.c
+++ b/nptl/pthread_rwlock_wrlock.c
@@ -16,114 +16,18 @@
    License along with the GNU C Library; if not, see
    <http://www.gnu.org/licenses/>.  */
 
-#include <errno.h>
-#include <sysdep.h>
-#include <lowlevellock.h>
-#include <futex-internal.h>
-#include <pthread.h>
-#include <pthreadP.h>
-#include <stap-probe.h>
-#include <elide.h>
-
-
-/* Acquire write lock for RWLOCK.  */
-static int __attribute__((noinline))
-__pthread_rwlock_wrlock_slow (pthread_rwlock_t *rwlock)
-{
-  int result = 0;
-  int futex_shared =
-      rwlock->__data.__shared == LLL_PRIVATE ? FUTEX_PRIVATE : FUTEX_SHARED;
-
-  /* Caller has taken the lock.  */
-
-  while (1)
-    {
-      /* Make sure we are not holding the rwlock as a writer.  This is
-	 a deadlock situation we recognize and report.  */
-      if (__builtin_expect (rwlock->__data.__writer
-			    == THREAD_GETMEM (THREAD_SELF, tid), 0))
-	{
-	  result = EDEADLK;
-	  break;
-	}
-
-      /* Remember that we are a writer.  */
-      if (++rwlock->__data.__nr_writers_queued == 0)
-	{
-	  /* Overflow on number of queued writers.  */
-	  --rwlock->__data.__nr_writers_queued;
-	  result = EAGAIN;
-	  break;
-	}
-
-      int waitval = rwlock->__data.__writer_wakeup;
-
-      /* Free the lock.  */
-      lll_unlock (rwlock->__data.__lock, rwlock->__data.__shared);
-
-      /* Wait for the writer or reader(s) to finish.  We do not check the
-	 return value because we decide how to continue based on the state of
-	 the rwlock.  */
-      futex_wait_simple (&rwlock->__data.__writer_wakeup, waitval,
-			 futex_shared);
-
-      /* Get the lock.  */
-      lll_lock (rwlock->__data.__lock, rwlock->__data.__shared);
-
-      /* To start over again, remove the thread from the writer list.  */
-      --rwlock->__data.__nr_writers_queued;
-
-      /* Get the rwlock if there is no writer and no reader.  */
-      if (rwlock->__data.__writer == 0 && rwlock->__data.__nr_readers == 0)
-	{
-	  /* Mark self as writer.  */
-	  rwlock->__data.__writer = THREAD_GETMEM (THREAD_SELF, tid);
-
-	  LIBC_PROBE (wrlock_acquire_write, 1, rwlock);
-	  break;
-	}
-    }
-
-  /* We are done, free the lock.  */
-  lll_unlock (rwlock->__data.__lock, rwlock->__data.__shared);
-
-  return result;
-}
-
-/* Fast path of acquiring write lock for RWLOCK.  */
+#include "pthread_rwlock_common.c"
 
+/* See pthread_rwlock_common.c.  */
 int
 __pthread_rwlock_wrlock (pthread_rwlock_t *rwlock)
 {
   LIBC_PROBE (wrlock_entry, 1, rwlock);
 
-  if (ELIDE_LOCK (rwlock->__data.__rwelision,
-		  rwlock->__data.__lock == 0
-		  && rwlock->__data.__writer == 0
-		  && rwlock->__data.__nr_readers == 0))
-    return 0;
-
-  /* Make sure we are alone.  */
-  lll_lock (rwlock->__data.__lock, rwlock->__data.__shared);
-
-  /* Get the rwlock if there is no writer and no reader.  */
-  if (__glibc_likely((rwlock->__data.__writer |
-	rwlock->__data.__nr_readers) == 0))
-    {
-      /* Mark self as writer.  */
-      rwlock->__data.__writer = THREAD_GETMEM (THREAD_SELF, tid);
-
-      LIBC_PROBE (wrlock_acquire_write, 1, rwlock);
-
-      /* We are done, free the lock.  */
-      lll_unlock (rwlock->__data.__lock, rwlock->__data.__shared);
-
-      return 0;
-    }
-
-  return __pthread_rwlock_wrlock_slow (rwlock);
+  int result = __pthread_rwlock_wrlock_full (rwlock, NULL);
+  LIBC_PROBE (wrlock_acquire_write, 1, rwlock);
+  return result;
 }
 
-
 weak_alias (__pthread_rwlock_wrlock, pthread_rwlock_wrlock)
 hidden_def (__pthread_rwlock_wrlock)
diff --git a/nptl/test-rwlock-printers.py b/nptl/test-rwlock-printers.py
index d7d2abe525..c19c92d48f 100644
--- a/nptl/test-rwlock-printers.py
+++ b/nptl/test-rwlock-printers.py
@@ -35,9 +35,9 @@ try:
 
     break_at(test_source, 'Test locking (reader)')
     continue_cmd() # Go to test_locking_reader
-    test_printer(var, to_string, {'Status': 'Unlocked'})
+    test_printer(var, to_string, {'Status': 'Not acquired'})
     next_cmd()
-    test_printer(var, to_string, {'Status': r'Locked \(Read\)', 'Readers': '1'})
+    test_printer(var, to_string, {'Status': r'Acquired \(Read\)', 'Readers': '1'})
     next_cmd()
     test_printer(var, to_string, {'Readers': '2'})
     next_cmd()
@@ -45,10 +45,10 @@ try:
 
     break_at(test_source, 'Test locking (writer)')
     continue_cmd() # Go to test_locking_writer
-    test_printer(var, to_string, {'Status': 'Unlocked'})
+    test_printer(var, to_string, {'Status': 'Not acquired'})
     next_cmd()
     thread_id = get_current_thread_lwpid()
-    test_printer(var, to_string, {'Status': r'Locked \(Write\)',
+    test_printer(var, to_string, {'Status': r'Acquired \(Write\)',
                                   'Writer ID': thread_id})
 
     continue_cmd() # Exit
diff --git a/nptl/test-rwlockattr-printers.c b/nptl/test-rwlockattr-printers.c
index aeb6af6ca1..b2cfc26b9e 100644
--- a/nptl/test-rwlockattr-printers.c
+++ b/nptl/test-rwlockattr-printers.c
@@ -75,6 +75,8 @@ test_setkind_np (pthread_rwlock_t *rwlock, pthread_rwlockattr_t *attr)
 
   if (SET_KIND (attr, PTHREAD_RWLOCK_PREFER_READER_NP) == 0 /* Set kind.  */
       && rwlock_reinit (rwlock, attr) == PASS
+      && SET_KIND (attr, PTHREAD_RWLOCK_PREFER_WRITER_NP) == 0
+      && rwlock_reinit (rwlock, attr) == PASS
       && SET_KIND (attr, PTHREAD_RWLOCK_PREFER_WRITER_NONRECURSIVE_NP) == 0
       && rwlock_reinit (rwlock, attr) == PASS)
     result = PASS;
diff --git a/nptl/test-rwlockattr-printers.py b/nptl/test-rwlockattr-printers.py
index 9db3c25305..e62e5c533f 100644
--- a/nptl/test-rwlockattr-printers.py
+++ b/nptl/test-rwlockattr-printers.py
@@ -46,6 +46,9 @@ try:
     next_cmd(2)
     test_printer(rwlock_var, rwlock_to_string, {'Prefers': 'Writers'})
     test_printer(attr_var, attr_to_string, {'Prefers': 'Writers'})
+    next_cmd(2)
+    test_printer(rwlock_var, rwlock_to_string, {'Prefers': 'Writers no recursive readers'})
+    test_printer(attr_var, attr_to_string, {'Prefers': 'Writers no recursive readers'})
 
     break_at(test_source, 'Set shared')
     continue_cmd() # Go to test_setpshared
diff --git a/nptl/tst-rwlock10.c b/nptl/tst-rwlock10.c
index e2c47d39a2..0726458a19 100644
--- a/nptl/tst-rwlock10.c
+++ b/nptl/tst-rwlock10.c
@@ -16,5 +16,5 @@
    License along with the GNU C Library; see the file COPYING.LIB.  If
    not, see <http://www.gnu.org/licenses/>.  */
 
-#define INIT PTHREAD_RWLOCK_INITIALIZER
+#define KIND PTHREAD_RWLOCK_PREFER_READER_NP
 #include "tst-rwlock8.c"
diff --git a/nptl/tst-rwlock11.c b/nptl/tst-rwlock11.c
index 8d3456521f..bcd435803a 100644
--- a/nptl/tst-rwlock11.c
+++ b/nptl/tst-rwlock11.c
@@ -16,5 +16,5 @@
    License along with the GNU C Library; see the file COPYING.LIB.  If
    not, see <http://www.gnu.org/licenses/>.  */
 
-#define INIT PTHREAD_RWLOCK_INITIALIZER
+#define KIND PTHREAD_RWLOCK_PREFER_READER_NP
 #include "tst-rwlock9.c"
diff --git a/nptl/tst-rwlock17.c b/nptl/tst-rwlock17.c
new file mode 100644
index 0000000000..50c87e1f11
--- /dev/null
+++ b/nptl/tst-rwlock17.c
@@ -0,0 +1,19 @@
+/* Test program for timedout read/write lock functions.
+   Copyright (C) 2016-2017 Free Software Foundation, Inc.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public License as
+   published by the Free Software Foundation; either version 2.1 of the
+   License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; see the file COPYING.LIB.  If
+   not, see <http://www.gnu.org/licenses/>.  */
+
+#define KIND PTHREAD_RWLOCK_PREFER_WRITER_NP
+#include "tst-rwlock8.c"
diff --git a/nptl/tst-rwlock18.c b/nptl/tst-rwlock18.c
new file mode 100644
index 0000000000..c07935c56e
--- /dev/null
+++ b/nptl/tst-rwlock18.c
@@ -0,0 +1,19 @@
+/* Test program for timedout read/write lock functions.
+   Copyright (C) 2016-2017 Free Software Foundation, Inc.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public License as
+   published by the Free Software Foundation; either version 2.1 of the
+   License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; see the file COPYING.LIB.  If
+   not, see <http://www.gnu.org/licenses/>.  */
+
+#define KIND PTHREAD_RWLOCK_PREFER_WRITER_NP
+#include "tst-rwlock9.c"
diff --git a/nptl/tst-rwlock19.c b/nptl/tst-rwlock19.c
new file mode 100644
index 0000000000..746d84d92f
--- /dev/null
+++ b/nptl/tst-rwlock19.c
@@ -0,0 +1,127 @@
+/* Test rdlock overflow.
+   Copyright (C) 2000-2017 Free Software Foundation, Inc.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public License as
+   published by the Free Software Foundation; either version 2.1 of the
+   License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; see the file COPYING.LIB.  If
+   not, see <http://www.gnu.org/licenses/>.  */
+
+#include <errno.h>
+#include <error.h>
+#include <pthread.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <time.h>
+#include <unistd.h>
+#include <pthreadP.h>
+
+
+#define NREADERS 15
+#define READTRIES 5000
+
+#define DELAY   1000000
+
+static pthread_rwlock_t lock = PTHREAD_RWLOCK_INITIALIZER;
+static int eagain_returned = 0;
+static int success_returned = 0;
+
+static void *
+reader_thread (void *nr)
+{
+  struct timespec delay;
+  int n;
+
+  delay.tv_sec = 0;
+  delay.tv_nsec = DELAY;
+
+  for (n = 0; n < READTRIES; ++n)
+    {
+      int err = pthread_rwlock_rdlock (&lock);
+      if (err == EAGAIN)
+	{
+	  atomic_store_relaxed (&eagain_returned, 1);
+	  continue;
+	}
+      else if (err == 0)
+	atomic_store_relaxed (&success_returned, 1);
+      else
+	{
+	  puts ("rdlock failed");
+	  exit (1);
+	}
+
+      nanosleep (&delay, NULL);
+
+      if (pthread_rwlock_unlock (&lock) != 0)
+	{
+	  puts ("unlock for reader failed");
+	  exit (1);
+	}
+    }
+
+  return NULL;
+}
+
+
+static int
+do_test (void)
+{
+  pthread_t thrd[NREADERS];
+  int n;
+  void *res;
+
+  /* Set the rwlock so that it's close to a reader overflow.
+     PTHREAD_RWLOCK_WRPHASE and PTHREAD_RWLOCK_WRLOCK are zero initially.  */
+  unsigned int readers = PTHREAD_RWLOCK_READER_OVERFLOW
+      - ((NREADERS / 3) << PTHREAD_RWLOCK_READER_SHIFT);
+  lock.__data.__readers = readers;
+
+  for (n = 0; n < NREADERS; ++n)
+    if (pthread_create (&thrd[n], NULL, reader_thread,
+			(void *) (long int) n) != 0)
+      {
+	puts ("reader create failed");
+	exit (1);
+      }
+
+  /* Wait for all the threads.  */
+  for (n = 0; n < NREADERS; ++n)
+    if (pthread_join (thrd[n], &res) != 0)
+      {
+	puts ("reader join failed");
+	exit (1);
+      }
+
+  if (atomic_load_relaxed (&eagain_returned) == 0)
+    {
+      puts ("EAGAIN has never been returned");
+      exit (1);
+    }
+
+  if (atomic_load_relaxed (&success_returned) == 0)
+    {
+      puts ("rdlock was never successfully acquired");
+      exit (1);
+    }
+
+  if (lock.__data.__readers != readers)
+    {
+      puts ("__readers in rwlock differs from initial value");
+      exit (1);
+    }
+
+  return 0;
+}
+
+#define TIMEOUT 30
+#define TEST_FUNCTION do_test ()
+#include "../test-skeleton.c"
diff --git a/nptl/tst-rwlock2b.c b/nptl/tst-rwlock2b.c
new file mode 100644
index 0000000000..5ebaa3a546
--- /dev/null
+++ b/nptl/tst-rwlock2b.c
@@ -0,0 +1,2 @@
+#define TYPE PTHREAD_RWLOCK_PREFER_WRITER_NP
+#include "tst-rwlock2.c"
diff --git a/nptl/tst-rwlock8.c b/nptl/tst-rwlock8.c
index 9baecac877..5f3174d46a 100644
--- a/nptl/tst-rwlock8.c
+++ b/nptl/tst-rwlock8.c
@@ -32,11 +32,11 @@
 
 #define DELAY   1000000
 
-#ifndef INIT
-# define INIT PTHREAD_RWLOCK_WRITER_NONRECURSIVE_INITIALIZER_NP
+#ifndef KIND
+# define KIND PTHREAD_RWLOCK_PREFER_WRITER_NONRECURSIVE_NP
 #endif
 
-static pthread_rwlock_t lock = INIT;
+static pthread_rwlock_t lock;
 
 
 static void *
@@ -118,6 +118,25 @@ do_test (void)
   pthread_t thrd[NREADERS];
   int n;
   void *res;
+  pthread_rwlockattr_t a;
+
+  if (pthread_rwlockattr_init (&a) != 0)
+    {
+      puts ("rwlockattr_t failed");
+      exit (1);
+    }
+
+  if (pthread_rwlockattr_setkind_np (&a, KIND) != 0)
+    {
+      puts ("rwlockattr_setkind failed");
+      exit (1);
+    }
+
+  if (pthread_rwlock_init (&lock, &a) != 0)
+    {
+      puts ("rwlock_init failed");
+      exit (1);
+    }
 
   /* Make standard error the same as standard output.  */
   dup2 (1, 2);
diff --git a/nptl/tst-rwlock9.c b/nptl/tst-rwlock9.c
index ae2fd96bd2..a7ea34fae6 100644
--- a/nptl/tst-rwlock9.c
+++ b/nptl/tst-rwlock9.c
@@ -34,11 +34,11 @@
 #define TIMEOUT 1000000
 #define DELAY   1000000
 
-#ifndef INIT
-# define INIT PTHREAD_RWLOCK_WRITER_NONRECURSIVE_INITIALIZER_NP
+#ifndef KIND
+# define KIND PTHREAD_RWLOCK_PREFER_WRITER_NONRECURSIVE_NP
 #endif
 
-static pthread_rwlock_t lock = INIT;
+static pthread_rwlock_t lock;
 
 
 static void *
@@ -156,6 +156,25 @@ do_test (void)
   pthread_t thrd[NREADERS];
   int n;
   void *res;
+  pthread_rwlockattr_t a;
+
+  if (pthread_rwlockattr_init (&a) != 0)
+    {
+      puts ("rwlockattr_t failed");
+      exit (1);
+    }
+
+  if (pthread_rwlockattr_setkind_np (&a, KIND) != 0)
+    {
+      puts ("rwlockattr_setkind failed");
+      exit (1);
+    }
+
+  if (pthread_rwlock_init (&lock, &a) != 0)
+    {
+      puts ("rwlock_init failed");
+      exit (1);
+    }
 
   /* Make standard error the same as standard output.  */
   dup2 (1, 2);