pthread: Move some rwlock tests from nptl to sysdeps/pthread

So they can be checked with htl too.

8 files changed, 1106 insertions, 0 deletions

diff --git a/sysdeps/pthread/Makefile b/sysdeps/pthread/Makefile
index 6b49e33bdc..cceaa91837 100644
--- a/sysdeps/pthread/Makefile
+++ b/sysdeps/pthread/Makefile
@@ -52,6 +52,8 @@ tests += tst-cnd-basic tst-mtx-trylock tst-cnd-broadcast \
 	 tst-cond-except \
 	 tst-mutex1 tst-mutex2 tst-mutex3 tst-mutex4 tst-mutex6 tst-mutex10 \
 	 tst-once1 tst-once2 tst-once3 tst-once4 \
+	 tst-rwlock1 tst-rwlock4 tst-rwlock5 tst-rwlock13 tst-rwlock16 \
+	 tst-rwlock-tryrdlock-stall tst-rwlock-trywrlock-stall \
 	 tst-spin1 tst-spin2 tst-spin3 tst-spin4
 
 tests += tst-oncex3 tst-oncex4
diff --git a/sysdeps/pthread/tst-rwlock-tryrdlock-stall.c b/sysdeps/pthread/tst-rwlock-tryrdlock-stall.c
new file mode 100644
index 0000000000..bb2a64f301
--- /dev/null
+++ b/sysdeps/pthread/tst-rwlock-tryrdlock-stall.c
@@ -0,0 +1,355 @@
+/* Bug 23844: Test for pthread_rwlock_tryrdlock stalls.
+   Copyright (C) 2019-2020 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
+   <https://www.gnu.org/licenses/>.  */
+
+/* For a full analysis see comment:
+   https://sourceware.org/bugzilla/show_bug.cgi?id=23844#c14
+
+   Provided here for reference:
+
+   --- Analysis of pthread_rwlock_tryrdlock() stall ---
+   A read lock begins to execute.
+
+   In __pthread_rwlock_rdlock_full:
+
+   We can attempt a read lock, but find that the lock is
+   in a write phase (PTHREAD_RWLOCK_WRPHASE, or WP-bit
+   is set), and the lock is held by a primary writer
+   (PTHREAD_RWLOCK_WRLOCKED is set). In this case we must
+   wait for explicit hand over from the writer to us or
+   one of the other waiters. The read lock threads are
+   about to execute:
+
+   341   r = (atomic_fetch_add_acquire (&rwlock->__data.__readers,
+   342                                  (1 << PTHREAD_RWLOCK_READER_SHIFT))
+   343        + (1 << PTHREAD_RWLOCK_READER_SHIFT));
+
+   An unlock beings to execute.
+
+   Then in __pthread_rwlock_wrunlock:
+
+   547   unsigned int r = atomic_load_relaxed (&rwlock->__data.__readers);
+   ...
+   549   while (!atomic_compare_exchange_weak_release
+   550          (&rwlock->__data.__readers, &r,
+   551           ((r ^ PTHREAD_RWLOCK_WRLOCKED)
+   552            ^ ((r >> PTHREAD_RWLOCK_READER_SHIFT) == 0 ? 0
+   553               : PTHREAD_RWLOCK_WRPHASE))))
+   554     {
+   ...
+   556     }
+
+   We clear PTHREAD_RWLOCK_WRLOCKED, and if there are
+   no readers so we leave the lock in PTHRAD_RWLOCK_WRPHASE.
+
+   Back in the read lock.
+
+   The read lock adjusts __readres as above.
+
+   383   while ((r & PTHREAD_RWLOCK_WRPHASE) != 0
+   384          && (r & PTHREAD_RWLOCK_WRLOCKED) == 0)
+   385     {
+   ...
+   390       if (atomic_compare_exchange_weak_acquire (&rwlock->__data.__readers, &r,
+   391                                                 r ^ PTHREAD_RWLOCK_WRPHASE))
+   392         {
+
+   And then attemps to start the read phase.
+
+   Assume there happens to be a tryrdlock at this point, noting
+   that PTHREAD_RWLOCK_WRLOCKED is clear, and PTHREAD_RWLOCK_WRPHASE
+   is 1. So the try lock attemps to start the read phase.
+
+   In __pthread_rwlock_tryrdlock:
+
+    44       if ((r & PTHREAD_RWLOCK_WRPHASE) == 0)
+    45         {
+   ...
+    49           if (((r & PTHREAD_RWLOCK_WRLOCKED) != 0)
+    50               && (rwlock->__data.__flags
+    51                   == PTHREAD_RWLOCK_PREFER_WRITER_NONRECURSIVE_NP))
+    52             return EBUSY;
+    53           rnew = r + (1 << PTHREAD_RWLOCK_READER_SHIFT);
+    54         }
+   ...
+    89   while (!atomic_compare_exchange_weak_acquire (&rwlock->__data.__readers,
+    90       &r, rnew));
+
+   And succeeds.
+
+   Back in the write unlock:
+
+   557   if ((r >> PTHREAD_RWLOCK_READER_SHIFT) != 0)
+   558     {
+   ...
+   563       if ((atomic_exchange_relaxed (&rwlock->__data.__wrphase_futex, 0)
+   564            & PTHREAD_RWLOCK_FUTEX_USED) != 0)
+   565         futex_wake (&rwlock->__data.__wrphase_futex, INT_MAX, private);
+   566     }
+
+   We note that PTHREAD_RWLOCK_FUTEX_USED is non-zero
+   and don't wake anyone. This is OK because we handed
+   over to the trylock. It will be the trylock's responsibility
+   to wake any waiters.
+
+   Back in the read lock:
+
+   The read lock fails to install PTHRAD_REWLOCK_WRPHASE as 0 because
+   the __readers value was adjusted by the trylock, and so it falls through
+   to waiting on the lock for explicit handover from either a new writer
+   or a new reader.
+
+   448           int err = futex_abstimed_wait (&rwlock->__data.__wrphase_futex,
+   449                                          1 | PTHREAD_RWLOCK_FUTEX_USED,
+   450                                          abstime, private);
+
+   We use PTHREAD_RWLOCK_FUTEX_USED to indicate the futex
+   is in use.
+
+   At this point we have readers waiting on the read lock
+   to unlock. The wrlock is done. The trylock is finishing
+   the installation of the read phase.
+
+    92   if ((r & PTHREAD_RWLOCK_WRPHASE) != 0)
+    93     {
+   ...
+   105       atomic_store_relaxed (&rwlock->__data.__wrphase_futex, 0);
+   106     }
+
+   The trylock does note that we were the one that
+   installed the read phase, but the comments are not
+   correct, the execution ordering above shows that
+   readers might indeed be waiting, and they are.
+
+   The atomic_store_relaxed throws away PTHREAD_RWLOCK_FUTEX_USED,
+   and the waiting reader is never worken becuase as noted
+   above it is conditional on the futex being used.
+
+   The solution is for the trylock thread to inspect
+   PTHREAD_RWLOCK_FUTEX_USED and wake the waiting readers.
+
+   --- Analysis of pthread_rwlock_trywrlock() stall ---
+
+   A write lock begins to execute, takes the write lock,
+   and then releases the lock...
+
+   In pthread_rwlock_wrunlock():
+
+   547   unsigned int r = atomic_load_relaxed (&rwlock->__data.__readers);
+   ...
+   549   while (!atomic_compare_exchange_weak_release
+   550          (&rwlock->__data.__readers, &r,
+   551           ((r ^ PTHREAD_RWLOCK_WRLOCKED)
+   552            ^ ((r >> PTHREAD_RWLOCK_READER_SHIFT) == 0 ? 0
+   553               : PTHREAD_RWLOCK_WRPHASE))))
+   554     {
+   ...
+   556     }
+
+   ... leaving it in the write phase with zero readers
+   (the case where we leave the write phase in place
+   during a write unlock).
+
+   A write trylock begins to execute.
+
+   In __pthread_rwlock_trywrlock:
+
+    40   while (((r & PTHREAD_RWLOCK_WRLOCKED) == 0)
+    41       && (((r >> PTHREAD_RWLOCK_READER_SHIFT) == 0)
+    42           || (prefer_writer && ((r & PTHREAD_RWLOCK_WRPHASE) != 0))))
+    43     {
+
+   The lock is not locked.
+
+   There are no readers.
+
+    45       if (atomic_compare_exchange_weak_acquire (
+    46           &rwlock->__data.__readers, &r,
+    47           r | PTHREAD_RWLOCK_WRPHASE | PTHREAD_RWLOCK_WRLOCKED))
+
+   We atomically install the write phase and we take the
+   exclusive write lock.
+
+    48         {
+    49           atomic_store_relaxed (&rwlock->__data.__writers_futex, 1);
+
+   We get this far.
+
+   A reader lock begins to execute.
+
+   In pthread_rwlock_rdlock:
+
+   437   for (;;)
+   438     {
+   439       while (((wpf = atomic_load_relaxed (&rwlock->__data.__wrphase_futex))
+   440               | PTHREAD_RWLOCK_FUTEX_USED) == (1 | PTHREAD_RWLOCK_FUTEX_USED))
+   441         {
+   442           int private = __pthread_rwlock_get_private (rwlock);
+   443           if (((wpf & PTHREAD_RWLOCK_FUTEX_USED) == 0)
+   444               && (!atomic_compare_exchange_weak_relaxed
+   445                   (&rwlock->__data.__wrphase_futex,
+   446                    &wpf, wpf | PTHREAD_RWLOCK_FUTEX_USED)))
+   447             continue;
+   448           int err = futex_abstimed_wait (&rwlock->__data.__wrphase_futex,
+   449                                          1 | PTHREAD_RWLOCK_FUTEX_USED,
+   450                                          abstime, private);
+
+   We are in a write phase, so the while() on line 439 is true.
+
+   The value of wpf does not have PTHREAD_RWLOCK_FUTEX_USED set
+   since this is the first reader to lock.
+
+   The atomic operation sets wpf with PTHREAD_RELOCK_FUTEX_USED
+   on the expectation that this reader will be woken during
+   the handoff.
+
+   Back in pthread_rwlock_trywrlock:
+
+    50           atomic_store_relaxed (&rwlock->__data.__wrphase_futex, 1);
+    51           atomic_store_relaxed (&rwlock->__data.__cur_writer,
+    52               THREAD_GETMEM (THREAD_SELF, tid));
+    53           return 0;
+    54         }
+   ...
+    57     }
+
+   We write 1 to __wrphase_futex discarding PTHREAD_RWLOCK_FUTEX_USED,
+   and so in the unlock we will not awaken the waiting reader.
+
+   The solution to this is to realize that if we did not start the write
+   phase we need not write 1 or any other value to __wrphase_futex.
+   This ensures that any readers (which saw __wrphase_futex != 0) can
+   set PTHREAD_RWLOCK_FUTEX_USED and this can be used at unlock to
+   wake them.
+
+   If we installed the write phase then all other readers are looping
+   here:
+
+   In __pthread_rwlock_rdlock_full:
+
+   437   for (;;)
+   438     {
+   439       while (((wpf = atomic_load_relaxed (&rwlock->__data.__wrphase_futex))
+   440               | PTHREAD_RWLOCK_FUTEX_USED) == (1 | PTHREAD_RWLOCK_FUTEX_USED))
+   441         {
+   ...
+   508     }
+
+   waiting for the write phase to be installed or removed before they
+   can begin waiting on __wrphase_futex (part of the algorithm), or
+   taking a concurrent read lock, and thus we can safely write 1 to
+   __wrphase_futex.
+
+   If we did not install the write phase then the readers may already
+   be waiting on the futex, the original writer wrote 1 to __wrphase_futex
+   as part of starting the write phase, and we cannot also write 1
+   without loosing the PTHREAD_RWLOCK_FUTEX_USED bit.
+
+   ---
+
+   Summary for the pthread_rwlock_tryrdlock() stall:
+
+   The stall is caused by pthread_rwlock_tryrdlock failing to check
+   that PTHREAD_RWLOCK_FUTEX_USED is set in the __wrphase_futex futex
+   and then waking the futex.
+
+   The fix for bug 23844 ensures that waiters on __wrphase_futex are
+   correctly woken.  Before the fix the test stalls as readers can
+   wait forever on __wrphase_futex.  */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <pthread.h>
+#include <support/xthread.h>
+#include <errno.h>
+
+/* We need only one lock to reproduce the issue. We will need multiple
+   threads to get the exact case where we have a read, try, and unlock
+   all interleaving to produce the case where the readers are waiting
+   and the try fails to wake them.  */
+pthread_rwlock_t onelock;
+
+/* The number of threads is arbitrary but empirically chosen to have
+   enough threads that we see the condition where waiting readers are
+   not woken by a successful tryrdlock.  */
+#define NTHREADS 32
+
+_Atomic int do_exit;
+
+void *
+run_loop (void *arg)
+{
+  int i = 0, ret;
+  while (!do_exit)
+    {
+      /* Arbitrarily choose if we are the writer or reader.  Choose a
+	 high enough ratio of readers to writers to make it likely
+	 that readers block (and eventually are susceptable to
+	 stalling).
+
+         If we are a writer, take the write lock, and then unlock.
+	 If we are a reader, try the lock, then lock, then unlock.  */
+      if ((i % 8) != 0)
+	xpthread_rwlock_wrlock (&onelock);
+      else
+	{
+	  if ((ret = pthread_rwlock_tryrdlock (&onelock)) != 0)
+	    {
+	      if (ret == EBUSY)
+		xpthread_rwlock_rdlock (&onelock);
+	      else
+		exit (EXIT_FAILURE);
+	    }
+	}
+      /* Thread does some work and then unlocks.  */
+      xpthread_rwlock_unlock (&onelock);
+      i++;
+    }
+  return NULL;
+}
+
+int
+do_test (void)
+{
+  int i;
+  pthread_t tids[NTHREADS];
+  xpthread_rwlock_init (&onelock, NULL);
+  for (i = 0; i < NTHREADS; i++)
+    tids[i] = xpthread_create (NULL, run_loop, NULL);
+  /* Run for some amount of time.  Empirically speaking exercising
+     the stall via pthread_rwlock_tryrdlock is much harder, and on
+     a 3.5GHz 4 core x86_64 VM system it takes somewhere around
+     20-200s to stall, approaching 100% stall past 200s.  We can't
+     wait that long for a regression test so we just test for 20s,
+     and expect the stall to happen with a 5-10% chance (enough for
+     developers to see).  */
+  sleep (20);
+  /* Then exit.  */
+  printf ("INFO: Exiting...\n");
+  do_exit = 1;
+  /* If any readers stalled then we will timeout waiting for them.  */
+  for (i = 0; i < NTHREADS; i++)
+    xpthread_join (tids[i]);
+  printf ("INFO: Done.\n");
+  xpthread_rwlock_destroy (&onelock);
+  printf ("PASS: No pthread_rwlock_tryrdlock stalls detected.\n");
+  return 0;
+}
+
+#define TIMEOUT 30
+#include <support/test-driver.c>
diff --git a/sysdeps/pthread/tst-rwlock-trywrlock-stall.c b/sysdeps/pthread/tst-rwlock-trywrlock-stall.c
new file mode 100644
index 0000000000..b4e60c5af3
--- /dev/null
+++ b/sysdeps/pthread/tst-rwlock-trywrlock-stall.c
@@ -0,0 +1,108 @@
+/* Bug 23844: Test for pthread_rwlock_trywrlock stalls.
+   Copyright (C) 2019-2020 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
+   <https://www.gnu.org/licenses/>.  */
+
+/* For a full analysis see comments in tst-rwlock-tryrdlock-stall.c.
+
+   Summary for the pthread_rwlock_trywrlock() stall:
+
+   The stall is caused by pthread_rwlock_trywrlock setting
+   __wrphase_futex futex to 1 and loosing the
+   PTHREAD_RWLOCK_FUTEX_USED bit.
+
+   The fix for bug 23844 ensures that waiters on __wrphase_futex are
+   correctly woken.  Before the fix the test stalls as readers can
+   wait forever on  __wrphase_futex.  */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <pthread.h>
+#include <support/xthread.h>
+#include <errno.h>
+
+/* We need only one lock to reproduce the issue. We will need multiple
+   threads to get the exact case where we have a read, try, and unlock
+   all interleaving to produce the case where the readers are waiting
+   and the try clears the PTHREAD_RWLOCK_FUTEX_USED bit and a
+   subsequent unlock fails to wake them.  */
+pthread_rwlock_t onelock;
+
+/* The number of threads is arbitrary but empirically chosen to have
+   enough threads that we see the condition where waiting readers are
+   not woken by a successful unlock.  */
+#define NTHREADS 32
+
+_Atomic int do_exit;
+
+void *
+run_loop (void *arg)
+{
+  int i = 0, ret;
+  while (!do_exit)
+    {
+      /* Arbitrarily choose if we are the writer or reader.  Choose a
+	 high enough ratio of readers to writers to make it likely
+	 that readers block (and eventually are susceptable to
+	 stalling).
+
+         If we are a writer, take the write lock, and then unlock.
+	 If we are a reader, try the lock, then lock, then unlock.  */
+      if ((i % 8) != 0)
+	{
+	  if ((ret = pthread_rwlock_trywrlock (&onelock)) != 0)
+	    {
+	      if (ret == EBUSY)
+		xpthread_rwlock_wrlock (&onelock);
+	      else
+		exit (EXIT_FAILURE);
+	    }
+	}
+      else
+	xpthread_rwlock_rdlock (&onelock);
+      /* Thread does some work and then unlocks.  */
+      xpthread_rwlock_unlock (&onelock);
+      i++;
+    }
+  return NULL;
+}
+
+int
+do_test (void)
+{
+  int i;
+  pthread_t tids[NTHREADS];
+  xpthread_rwlock_init (&onelock, NULL);
+  for (i = 0; i < NTHREADS; i++)
+    tids[i] = xpthread_create (NULL, run_loop, NULL);
+  /* Run for some amount of time.  The pthread_rwlock_tryrwlock stall
+     is very easy to trigger and happens in seconds under the test
+     conditions.  */
+  sleep (10);
+  /* Then exit.  */
+  printf ("INFO: Exiting...\n");
+  do_exit = 1;
+  /* If any readers stalled then we will timeout waiting for them.  */
+  for (i = 0; i < NTHREADS; i++)
+    xpthread_join (tids[i]);
+  printf ("INFO: Done.\n");
+  xpthread_rwlock_destroy (&onelock);
+  printf ("PASS: No pthread_rwlock_tryrwlock stalls detected.\n");
+  return 0;
+}
+
+#include <support/test-driver.c>
diff --git a/sysdeps/pthread/tst-rwlock1.c b/sysdeps/pthread/tst-rwlock1.c
new file mode 100644
index 0000000000..d14d3036a2
--- /dev/null
+++ b/sysdeps/pthread/tst-rwlock1.c
@@ -0,0 +1,116 @@
+/* Copyright (C) 2002-2020 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+   Contributed by Ulrich Drepper <drepper@redhat.com>, 2002.
+
+   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
+   <https://www.gnu.org/licenses/>.  */
+
+#include <pthread.h>
+#include <stdio.h>
+
+
+static int
+do_test (void)
+{
+  pthread_rwlock_t r;
+
+  if (pthread_rwlock_init (&r, NULL) != 0)
+    {
+      puts ("rwlock_init failed");
+      return 1;
+    }
+  puts ("rwlock_init succeeded");
+
+  if (pthread_rwlock_rdlock (&r) != 0)
+    {
+      puts ("1st rwlock_rdlock failed");
+      return 1;
+    }
+  puts ("1st rwlock_rdlock succeeded");
+
+  if (pthread_rwlock_rdlock (&r) != 0)
+    {
+      puts ("2nd rwlock_rdlock failed");
+      return 1;
+    }
+  puts ("2nd rwlock_rdlock succeeded");
+
+  if (pthread_rwlock_unlock (&r) != 0)
+    {
+      puts ("1st rwlock_unlock failed");
+      return 1;
+    }
+  puts ("1st rwlock_unlock succeeded");
+
+  if (pthread_rwlock_unlock (&r) != 0)
+    {
+      puts ("2nd rwlock_unlock failed");
+      return 1;
+    }
+  puts ("2nd rwlock_unlock succeeded");
+
+  if (pthread_rwlock_wrlock (&r) != 0)
+    {
+      puts ("1st rwlock_wrlock failed");
+      return 1;
+    }
+  puts ("1st rwlock_wrlock succeeded");
+
+  if (pthread_rwlock_unlock (&r) != 0)
+    {
+      puts ("3rd rwlock_unlock failed");
+      return 1;
+    }
+  puts ("3rd rwlock_unlock succeeded");
+
+  if (pthread_rwlock_wrlock (&r) != 0)
+    {
+      puts ("2nd rwlock_wrlock failed");
+      return 1;
+    }
+  puts ("2nd rwlock_wrlock succeeded");
+
+  if (pthread_rwlock_unlock (&r) != 0)
+    {
+      puts ("4th rwlock_unlock failed");
+      return 1;
+    }
+  puts ("4th rwlock_unlock succeeded");
+
+  if (pthread_rwlock_rdlock (&r) != 0)
+    {
+      puts ("3rd rwlock_rdlock failed");
+      return 1;
+    }
+  puts ("3rd rwlock_rdlock succeeded");
+
+  if (pthread_rwlock_unlock (&r) != 0)
+    {
+      puts ("5th rwlock_unlock failed");
+      return 1;
+    }
+  puts ("5th rwlock_unlock succeeded");
+
+  if (pthread_rwlock_destroy (&r) != 0)
+    {
+      puts ("rwlock_destroy failed");
+      return 1;
+    }
+  puts ("rwlock_destroy succeeded");
+
+  return 0;
+}
+
+#define TEST_FUNCTION do_test ()
+#include "../test-skeleton.c"
diff --git a/sysdeps/pthread/tst-rwlock13.c b/sysdeps/pthread/tst-rwlock13.c
new file mode 100644
index 0000000000..749ec4b621
--- /dev/null
+++ b/sysdeps/pthread/tst-rwlock13.c
@@ -0,0 +1,70 @@
+/* Copyright (C) 2004-2020 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
+   <https://www.gnu.org/licenses/>.  */
+
+#include <pthread.h>
+#include <stdio.h>
+#include <string.h>
+
+
+static int
+do_test (void)
+{
+  pthread_rwlock_t r;
+  int ret;
+
+  memset (&r, 0xaa, sizeof (r));
+  if ((ret = pthread_rwlock_init (&r, NULL)) != 0)
+    {
+      printf ("rwlock_init failed: %d\n", ret);
+      return 1;
+    }
+
+  if ((ret = pthread_rwlock_rdlock (&r)) != 0)
+    {
+      printf ("rwlock_rdlock failed: %d\n", ret);
+      return 1;
+    }
+
+  if ((ret = pthread_rwlock_unlock (&r)) != 0)
+    {
+      printf ("rwlock_unlock failed: %d\n", ret);
+      return 1;
+    }
+
+  if ((ret = pthread_rwlock_wrlock (&r)) != 0)
+    {
+      printf ("rwlock_wrlock failed: %d\n", ret);
+      return 1;
+    }
+
+  if ((ret = pthread_rwlock_unlock (&r)) != 0)
+    {
+      printf ("second rwlock_unlock failed: %d\n", ret);
+      return 1;
+    }
+
+  if ((ret = pthread_rwlock_destroy (&r)) != 0)
+    {
+      printf ("second rwlock_destroy failed: %d\n", ret);
+      return 1;
+    }
+
+  return 0;
+}
+
+#define TEST_FUNCTION do_test ()
+#include "../test-skeleton.c"
diff --git a/sysdeps/pthread/tst-rwlock16.c b/sysdeps/pthread/tst-rwlock16.c
new file mode 100644
index 0000000000..29720c9d8d
--- /dev/null
+++ b/sysdeps/pthread/tst-rwlock16.c
@@ -0,0 +1,182 @@
+/* Copyright (C) 2015-2020 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
+   <https://www.gnu.org/licenses/>.  */
+
+/* This tests that with a reader-preferring rwlock, all readers are woken if
+   one reader "steals" lock ownership from a blocked writer.  */
+
+#include <errno.h>
+#include <pthread.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <semaphore.h>
+#include <unistd.h>
+
+/* If we strictly prefer writers over readers, a program must not expect
+   that, in the presence of concurrent writers, one reader will also acquire
+   the lock when another reader has already done so.  Thus, use the
+   default rwlock type that does not strictly prefer writers.  */
+static pthread_rwlock_t r = PTHREAD_RWLOCK_INITIALIZER;
+
+static pthread_mutex_t m = PTHREAD_MUTEX_INITIALIZER;
+static pthread_cond_t cv = PTHREAD_COND_INITIALIZER;
+
+/* Avoid using glibc-internal atomic operations.  */
+static sem_t stop;
+static int consumer_stop = 0;
+
+static void *
+writer (void *arg)
+{
+  int s;
+
+  do
+    {
+      if (pthread_rwlock_wrlock (&r) != 0)
+	{
+	  puts ("wrlock failed");
+	  exit (EXIT_FAILURE);
+	}
+      if (pthread_rwlock_unlock (&r) != 0)
+	{
+	  puts ("unlock failed");
+	  exit (EXIT_FAILURE);
+	}
+      sem_getvalue (&stop, &s);
+    }
+  while (s == 0);
+  return NULL;
+}
+
+static void *
+reader_producer (void *arg)
+{
+  int s;
+
+  do
+    {
+      if (pthread_rwlock_rdlock (&r) != 0)
+	{
+	  puts ("rdlock reader failed");
+	  exit (EXIT_FAILURE);
+	}
+
+      sem_getvalue (&stop, &s);
+
+      pthread_mutex_lock (&m);
+      if (s != 0)
+	consumer_stop = 1;
+      pthread_cond_signal (&cv);
+      pthread_mutex_unlock (&m);
+
+      if (pthread_rwlock_unlock (&r) != 0)
+	{
+	  puts ("unlock reader failed");
+	  exit (EXIT_FAILURE);
+	}
+    }
+  while (s == 0);
+  puts ("producer finished");
+  return NULL;
+}
+
+static void *
+reader_consumer (void *arg)
+{
+  int s;
+
+  do
+    {
+      if (pthread_rwlock_rdlock (&r) != 0)
+	{
+	  puts ("rdlock reader failed");
+	  exit (EXIT_FAILURE);
+	}
+
+      pthread_mutex_lock (&m);
+      s = consumer_stop;
+      if (s == 0)
+	pthread_cond_wait (&cv, &m);
+      pthread_mutex_unlock (&m);
+
+      if (pthread_rwlock_unlock (&r) != 0)
+	{
+	  puts ("unlock reader failed");
+	  exit (EXIT_FAILURE);
+	}
+    }
+  while (s == 0);
+    puts ("consumer finished");
+  return NULL;
+}
+
+
+static int
+do_test (void)
+{
+  pthread_t w1, w2, rp, rc;
+
+  if (pthread_create (&w1, NULL, writer, NULL) != 0)
+    {
+      puts ("create failed");
+      return 1;
+    }
+  if (pthread_create (&w2, NULL, writer, NULL) != 0)
+    {
+      puts ("create failed");
+      return 1;
+    }
+  if (pthread_create (&rc, NULL, reader_consumer, NULL) != 0)
+    {
+      puts ("create failed");
+      return 1;
+    }
+  if (pthread_create (&rp, NULL, reader_producer, NULL) != 0)
+    {
+      puts ("create failed");
+      return 1;
+    }
+
+  sleep (2);
+  sem_post (&stop);
+
+  if (pthread_join (w1, NULL) != 0)
+    {
+      puts ("w1 join failed");
+      return 1;
+    }
+  if (pthread_join (w2, NULL) != 0)
+    {
+      puts ("w2 join failed");
+      return 1;
+    }
+  if (pthread_join (rp, NULL) != 0)
+    {
+      puts ("reader_producer join failed");
+      return 1;
+    }
+  if (pthread_join (rc, NULL) != 0)
+    {
+      puts ("reader_consumer join failed");
+      return 1;
+    }
+
+  return 0;
+}
+
+
+#define TEST_FUNCTION do_test ()
+#include "../test-skeleton.c"
diff --git a/sysdeps/pthread/tst-rwlock4.c b/sysdeps/pthread/tst-rwlock4.c
new file mode 100644
index 0000000000..479107a5f2
--- /dev/null
+++ b/sysdeps/pthread/tst-rwlock4.c
@@ -0,0 +1,189 @@
+/* Copyright (C) 2002-2020 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+   Contributed by Ulrich Drepper <drepper@redhat.com>, 2002.
+
+   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
+   <https://www.gnu.org/licenses/>.  */
+
+#include <errno.h>
+#include <pthread.h>
+#include <stdint.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+#include <sys/mman.h>
+#include <sys/wait.h>
+
+
+static int
+do_test (void)
+{
+  size_t ps = sysconf (_SC_PAGESIZE);
+  char tmpfname[] = "/tmp/tst-rwlock4.XXXXXX";
+  char data[ps];
+  void *mem;
+  int fd;
+  pthread_rwlock_t *r;
+  pthread_rwlockattr_t a;
+  pid_t pid;
+  char *p;
+  int err;
+  int s;
+
+  fd = mkstemp (tmpfname);
+  if (fd == -1)
+    {
+      printf ("cannot open temporary file: %m\n");
+      return 1;
+    }
+
+  /* Make sure it is always removed.  */
+  unlink (tmpfname);
+
+  /* Create one page of data.  */
+  memset (data, '\0', ps);
+
+  /* Write the data to the file.  */
+  if (write (fd, data, ps) != (ssize_t) ps)
+    {
+      puts ("short write");
+      return 1;
+    }
+
+  mem = mmap (NULL, ps, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
+  if (mem == MAP_FAILED)
+    {
+      printf ("mmap failed: %m\n");
+      return 1;
+    }
+
+  r = (pthread_rwlock_t *) (((uintptr_t) mem + __alignof (pthread_rwlock_t))
+			    & ~(__alignof (pthread_rwlock_t) - 1));
+  p = (char *) (r + 1);
+
+  if (pthread_rwlockattr_init (&a) != 0)
+    {
+      puts ("rwlockattr_init failed");
+      return 1;
+    }
+
+  if (pthread_rwlockattr_getpshared (&a, &s) != 0)
+    {
+      puts ("1st rwlockattr_getpshared failed");
+      return 1;
+    }
+
+  if (s != PTHREAD_PROCESS_PRIVATE)
+    {
+      puts ("default pshared value wrong");
+      return 1;
+    }
+
+  if (pthread_rwlockattr_setpshared (&a, PTHREAD_PROCESS_SHARED) != 0)
+    {
+      puts ("rwlockattr_setpshared failed");
+      return 1;
+    }
+
+  if (pthread_rwlockattr_getpshared (&a, &s) != 0)
+    {
+      puts ("2nd rwlockattr_getpshared failed");
+      return 1;
+    }
+
+  if (s != PTHREAD_PROCESS_SHARED)
+    {
+      puts ("pshared value after setpshared call wrong");
+      return 1;
+    }
+
+  if (pthread_rwlock_init (r, &a) != 0)
+    {
+      puts ("rwlock_init failed");
+      return 1;
+    }
+
+  if (pthread_rwlock_rdlock (r) != 0)
+    {
+      puts ("rwlock_rdlock failed");
+      return 1;
+    }
+
+  if (pthread_rwlockattr_destroy (&a) != 0)
+    {
+      puts ("rwlockattr_destroy failed");
+      return 1;
+    }
+
+  err = pthread_rwlock_trywrlock (r);
+  if (err == 0)
+    {
+      puts ("rwlock_trywrlock succeeded");
+      return 1;
+    }
+  else if (err != EBUSY)
+    {
+      puts ("rwlock_trywrlock didn't return EBUSY");
+      return 1;
+    }
+
+  *p = 0;
+
+  puts ("going to fork now");
+  pid = fork ();
+  if (pid == -1)
+    {
+      puts ("fork failed");
+      return 1;
+    }
+  else if (pid == 0)
+    {
+      /* Play some lock ping-pong.  It's our turn to unlock first.  */
+      if ((*p)++ != 0)
+	{
+	  puts ("child: *p != 0");
+	  return 1;
+	}
+
+      if (pthread_rwlock_unlock (r) != 0)
+	{
+	  puts ("child: 1st rwlock_unlock failed");
+	  return 1;
+	}
+
+      puts ("child done");
+    }
+  else
+    {
+      if (pthread_rwlock_wrlock (r) != 0)
+	{
+	  puts ("parent: rwlock_wrlock failed");
+	  return 1;
+	}
+
+      if (*p != 1)
+	{
+	  puts ("*p != 1");
+	  return 1;
+	}
+
+      puts ("parent done");
+    }
+
+  return 0;
+}
+
+#define TEST_FUNCTION do_test ()
+#include "../test-skeleton.c"
diff --git a/sysdeps/pthread/tst-rwlock5.c b/sysdeps/pthread/tst-rwlock5.c
new file mode 100644
index 0000000000..c589764196
--- /dev/null
+++ b/sysdeps/pthread/tst-rwlock5.c
@@ -0,0 +1,84 @@
+/* Copyright (C) 2002-2020 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+   Contributed by Ulrich Drepper <drepper@redhat.com>, 2002.
+
+   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
+   <https://www.gnu.org/licenses/>.  */
+
+#include <pthread.h>
+#include <signal.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+
+static int do_test (void);
+
+#define TEST_FUNCTION do_test ()
+#include "../test-skeleton.c"
+
+static pthread_mutex_t m = PTHREAD_MUTEX_INITIALIZER;
+static pthread_rwlock_t r;
+
+
+static void *
+tf (void *arg)
+{
+  if (pthread_rwlock_wrlock (&r) == 0)
+    {
+      puts ("child: rwlock_wrlock succeeded");
+      exit (1);
+    }
+
+  puts ("child: rwlock_wrlock returned");
+
+  exit (1);
+}
+
+
+static int
+do_test (void)
+{
+  pthread_t th;
+
+  if (pthread_rwlock_init (&r, NULL) != 0)
+    {
+      puts ("rwlock_init failed");
+      return 1;
+    }
+
+  if (pthread_rwlock_wrlock (&r) != 0)
+    {
+      puts ("rwlock_wrlock failed");
+      return 1;
+    }
+
+  if (pthread_mutex_lock (&m) != 0)
+    {
+      puts ("mutex_lock failed");
+      return 1;
+    }
+
+  if (pthread_create (&th, NULL, tf, NULL) != 0)
+    {
+      puts ("create failed");
+      return 1;
+    }
+
+  delayed_exit (1);
+  /* This call should never return.  */
+  xpthread_mutex_lock (&m);
+
+  puts ("2nd mutex_lock returned");
+  return 1;
+}