about summary refs log tree commit diff
path: root/sysdeps/nptl
diff options
context:
space:
mode:
Diffstat (limited to 'sysdeps/nptl')
-rw-r--r--sysdeps/nptl/aio_misc.h16
-rw-r--r--sysdeps/nptl/fork.c3
-rw-r--r--sysdeps/nptl/futex-internal.h203
-rw-r--r--sysdeps/nptl/gai_misc.h16
4 files changed, 221 insertions, 17 deletions
diff --git a/sysdeps/nptl/aio_misc.h b/sysdeps/nptl/aio_misc.h
index d5d1c08d0f..4a6ebfc9b3 100644
--- a/sysdeps/nptl/aio_misc.h
+++ b/sysdeps/nptl/aio_misc.h
@@ -22,14 +22,14 @@
 
 #include <assert.h>
 #include <nptl/pthreadP.h>
-#include <lowlevellock.h>
+#include <futex-internal.h>
 
 #define DONT_NEED_AIO_MISC_COND	1
 
 #define AIO_MISC_NOTIFY(waitlist) \
   do {									      \
     if (*waitlist->counterp > 0 && --*waitlist->counterp == 0)		      \
-      lll_futex_wake (waitlist->counterp, 1, LLL_PRIVATE);		      \
+      futex_wake ((unsigned int *) waitlist->counterp, 1, FUTEX_PRIVATE);     \
   } while (0)
 
 #define AIO_MISC_WAIT(result, futex, timeout, cancel)			      \
@@ -48,9 +48,9 @@
 	int status;							      \
 	do								      \
 	  {								      \
-	    status = lll_futex_timed_wait (futexaddr, oldval, timeout,	      \
-					   LLL_PRIVATE);		      \
-	    if (status != -EWOULDBLOCK)					      \
+	    status = futex_reltimed_wait ((unsigned int *) futexaddr, oldval, \
+					  timeout, FUTEX_PRIVATE);	      \
+	    if (status != EAGAIN)					      \
 	      break;							      \
 									      \
 	    oldval = *futexaddr;					      \
@@ -60,12 +60,12 @@
 	if (cancel)							      \
 	  LIBC_CANCEL_RESET (oldtype);					      \
 									      \
-	if (status == -EINTR)						      \
+	if (status == EINTR)						      \
 	  result = EINTR;						      \
-	else if (status == -ETIMEDOUT)					      \
+	else if (status == ETIMEDOUT)					      \
 	  result = EAGAIN;						      \
 	else								      \
-	  assert (status == 0 || status == -EWOULDBLOCK);		      \
+	  assert (status == 0 || status == EAGAIN);			      \
 									      \
 	pthread_mutex_lock (&__aio_requests_mutex);			      \
       }									      \
diff --git a/sysdeps/nptl/fork.c b/sysdeps/nptl/fork.c
index 74482b7a38..2b9ae4b571 100644
--- a/sysdeps/nptl/fork.c
+++ b/sysdeps/nptl/fork.c
@@ -30,6 +30,7 @@
 #include <nptl/pthreadP.h>
 #include <fork.h>
 #include <arch-fork.h>
+#include <futex-internal.h>
 
 
 static void
@@ -219,7 +220,7 @@ __libc_fork (void)
 
 	  if (atomic_decrement_and_test (&allp->handler->refcntr)
 	      && allp->handler->need_signal)
-	    lll_futex_wake (&allp->handler->refcntr, 1, LLL_PRIVATE);
+	    futex_wake (&allp->handler->refcntr, 1, FUTEX_PRIVATE);
 
 	  allp = allp->next;
 	}
diff --git a/sysdeps/nptl/futex-internal.h b/sysdeps/nptl/futex-internal.h
new file mode 100644
index 0000000000..4f8c8fe72d
--- /dev/null
+++ b/sysdeps/nptl/futex-internal.h
@@ -0,0 +1,203 @@
+/* futex operations for glibc-internal use.  Stub version; do not include
+   this file directly.
+   Copyright (C) 2014-2015 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/>.  */
+
+#ifndef STUB_FUTEX_INTERNAL_H
+#define STUB_FUTEX_INTERNAL_H
+
+#include <sys/time.h>
+#include <stdio.h>
+#include <stdbool.h>
+#include <libc-internal.h>
+
+/* This file defines futex operations used internally in glibc.  A futex
+   consists of the so-called futex word in userspace, which is of type
+   unsigned int and represents an application-specific condition, and kernel
+   state associated with this particular futex word (e.g., wait queues).  The
+   futex operations we provide are wrappers for the futex syscalls and add
+   glibc-specific error checking of the syscall return value.  We abort on
+   error codes that are caused by bugs in glibc or in the calling application,
+   or when an error code is not known.  We return error codes that can arise
+   in correct executions to the caller.  Each operation calls out exactly the
+   return values that callers need to handle.
+
+   The private flag must be either FUTEX_PRIVATE or FUTEX_SHARED.
+   FUTEX_PRIVATE is always supported, and the implementation can internally
+   use FUTEX_SHARED when FUTEX_PRIVATE is requested.  FUTEX_SHARED is not
+   necessarily supported (use futex_supports_pshared to detect this).
+
+   We expect callers to only use these operations if futexes and the
+   specific futex operations being used are supported (e.g., FUTEX_SHARED).
+
+   Given that waking other threads waiting on a futex involves concurrent
+   accesses to the futex word, you must use atomic operations to access the
+   futex word.
+
+   Both absolute and relative timeouts can be used.  An absolute timeout
+   expires when the given specific point in time on the CLOCK_REALTIME clock
+   passes, or when it already has passed.  A relative timeout expires when
+   the given duration of time on the CLOCK_MONOTONIC clock passes.  Relative
+   timeouts may be imprecise (see futex_supports_exact_relative_timeouts).
+
+   Due to POSIX requirements on when synchronization data structures such
+   as mutexes or semaphores can be destroyed and due to the futex design
+   having separate fast/slow paths for wake-ups, we need to consider that
+   futex_wake calls might effectively target a data structure that has been
+   destroyed and reused for another object, or unmapped; thus, some
+   errors or spurious wake-ups can happen in correct executions that would
+   not be possible in a program using just a single futex whose lifetime
+   does not end before the program terminates.  For background, see:
+   https://sourceware.org/ml/libc-alpha/2014-04/msg00075.html
+   https://lkml.org/lkml/2014/11/27/472  */
+
+/* Defined this way for interoperability with lowlevellock.
+   FUTEX_PRIVATE must be zero because the initializers for pthread_mutex_t,
+   pthread_rwlock_t, and pthread_cond_t initialize the respective field of
+   those structures to zero, and we want FUTEX_PRIVATE to be the default.  */
+#define FUTEX_PRIVATE LLL_PRIVATE
+#define FUTEX_SHARED  LLL_SHARED
+#if FUTEX_PRIVATE != 0
+# error FUTEX_PRIVATE must be equal to 0
+#endif
+
+/* Returns EINVAL if PSHARED is neither PTHREAD_PROCESS_PRIVATE nor
+   PTHREAD_PROCESS_SHARED; otherwise, returns 0 if PSHARED is supported, and
+   ENOTSUP if not.  */
+static __always_inline int
+futex_supports_pshared (int pshared);
+
+/* Returns true if relative timeouts are robust to concurrent changes to the
+   system clock.  If this returns false, relative timeouts can still be used
+   but might be effectively longer or shorter than requested.  */
+static __always_inline bool
+futex_supports_exact_relative_timeouts (void);
+
+/* Atomically wrt other futex operations on the same futex, this blocks iff
+   the value *FUTEX_WORD matches the expected value.  This is
+   semantically equivalent to:
+     l = <get lock associated with futex> (FUTEX_WORD);
+     wait_flag = <get wait_flag associated with futex> (FUTEX_WORD);
+     lock (l);
+     val = atomic_load_relaxed (FUTEX_WORD);
+     if (val != expected) { unlock (l); return EAGAIN; }
+     atomic_store_relaxed (wait_flag, true);
+     unlock (l);
+     // Now block; can time out in futex_time_wait (see below)
+     while (atomic_load_relaxed(wait_flag) && !<spurious wake-up>);
+
+   Note that no guarantee of a happens-before relation between a woken
+   futex_wait and a futex_wake is documented; however, this does not matter
+   in practice because we have to consider spurious wake-ups (see below),
+   and thus would not be able to reliably reason about which futex_wake woke
+   us.
+
+   Returns 0 if woken by a futex operation or spuriously.  (Note that due to
+   the POSIX requirements mentioned above, we need to conservatively assume
+   that unrelated futex_wake operations could wake this futex; it is easiest
+   to just be prepared for spurious wake-ups.)
+   Returns EAGAIN if the futex word did not match the expected value.
+   Returns EINTR if waiting was interrupted by a signal.
+
+   Note that some previous code in glibc assumed the underlying futex
+   operation (e.g., syscall) to start with or include the equivalent of a
+   seq_cst fence; this allows one to avoid an explicit seq_cst fence before
+   a futex_wait call when synchronizing similar to Dekker synchronization.
+   However, we make no such guarantee here.  */
+static __always_inline int
+futex_wait (unsigned int *futex_word, unsigned int expected, int private);
+
+/* Like futex_wait but does not provide any indication why we stopped waiting.
+   Thus, when this function returns, you have to always check FUTEX_WORD to
+   determine whether you need to continue waiting, and you cannot detect
+   whether the waiting was interrupted by a signal.  Example use:
+     while (atomic_load_relaxed (&futex_word) == 23)
+       futex_wait_simple (&futex_word, 23, FUTEX_PRIVATE);
+   This is common enough to make providing this wrapper worthwhile.  */
+static __always_inline void
+futex_wait_simple (unsigned int *futex_word, unsigned int expected,
+		   int private)
+{
+  ignore_value (futex_wait (futex_word, expected, private));
+}
+
+
+/* Like futex_wait but is a POSIX cancellation point.  */
+static __always_inline int
+futex_wait_cancelable (unsigned int *futex_word, unsigned int expected,
+		       int private);
+
+/* Like futex_wait, but will eventually time out (i.e., stop being
+   blocked) after the duration of time provided (i.e., RELTIME) has
+   passed.  The caller must provide a normalized RELTIME.  RELTIME can also
+   equal NULL, in which case this function behaves equivalent to futex_wait.
+
+   Returns the same values as futex_wait under those same conditions;
+   additionally, returns ETIMEDOUT if the timeout expired.
+   */
+static __always_inline int
+futex_reltimed_wait (unsigned int* futex_word, unsigned int expected,
+		     const struct timespec* reltime, int private);
+
+/* Like futex_reltimed_wait but is a POSIX cancellation point.  */
+static __always_inline int
+futex_reltimed_wait_cancelable (unsigned int* futex_word,
+				unsigned int expected,
+			        const struct timespec* reltime, int private);
+
+/* Like futex_reltimed_wait, but the provided timeout (ABSTIME) is an
+   absolute point in time; a call will time out after this point in time.  */
+static __always_inline int
+futex_abstimed_wait (unsigned int* futex_word, unsigned int expected,
+		     const struct timespec* abstime, int private);
+
+/* Like futex_reltimed_wait but is a POSIX cancellation point.  */
+static __always_inline int
+futex_abstimed_wait_cancelable (unsigned int* futex_word,
+				unsigned int expected,
+			        const struct timespec* abstime, int private);
+
+/* Atomically wrt other futex operations on the same futex, this unblocks the
+   specified number of processes, or all processes blocked on this futex if
+   there are fewer than the specified number.  Semantically, this is
+   equivalent to:
+     l = <get lock associated with futex> (FUTEX_WORD);
+     lock (l);
+     for (res = 0; PROCESSES_TO_WAKE > 0; PROCESSES_TO_WAKE--, res++) {
+       if (<no process blocked on futex>) break;
+       wf = <get wait_flag of a process blocked on futex> (FUTEX_WORD);
+       // No happens-before guarantee with woken futex_wait (see above)
+       atomic_store_relaxed (wf, 0);
+     }
+     return res;
+
+   Note that we need to support futex_wake calls to past futexes whose memory
+   has potentially been reused due to POSIX' requirements on synchronization
+   object destruction (see above); therefore, we must not report or abort
+   on most errors.  */
+static __always_inline void
+futex_wake (unsigned int* futex_word, int processes_to_wake, int private);
+
+/* Calls __libc_fatal with an error message.  Convenience function for
+   concrete implementations of the futex interface.  */
+static __always_inline __attribute__ ((__noreturn__)) void
+futex_fatal_error (void)
+{
+  __libc_fatal ("The futex facility returned an unexpected error code.");
+}
+
+#endif  /* futex-internal.h */
diff --git a/sysdeps/nptl/gai_misc.h b/sysdeps/nptl/gai_misc.h
index a34dbc0dd9..96c8fa0f91 100644
--- a/sysdeps/nptl/gai_misc.h
+++ b/sysdeps/nptl/gai_misc.h
@@ -23,14 +23,14 @@
 #include <assert.h>
 #include <signal.h>
 #include <nptl/pthreadP.h>
-#include <lowlevellock.h>
+#include <futex-internal.h>
 
 #define DONT_NEED_GAI_MISC_COND	1
 
 #define GAI_MISC_NOTIFY(waitlist) \
   do {									      \
     if (*waitlist->counterp > 0 && --*waitlist->counterp == 0)		      \
-      lll_futex_wake (waitlist->counterp, 1, LLL_PRIVATE);		      \
+      futex_wake ((unsigned int *) waitlist->counterp, 1, FUTEX_PRIVATE);     \
   } while (0)
 
 #define GAI_MISC_WAIT(result, futex, timeout, cancel) \
@@ -49,9 +49,9 @@
 	int status;							      \
 	do								      \
 	  {								      \
-	    status = lll_futex_timed_wait (futexaddr, oldval, timeout,	      \
-					   LLL_PRIVATE);		      \
-	    if (status != -EWOULDBLOCK)					      \
+	    status = futex_reltimed_wait ((unsigned int *) futexaddr, oldval, \
+					  timeout, FUTEX_PRIVATE);	      \
+	    if (status != EAGAIN)					      \
 	      break;							      \
 									      \
 	    oldval = *futexaddr;					      \
@@ -61,12 +61,12 @@
 	if (cancel)							      \
 	  LIBC_CANCEL_RESET (oldtype);					      \
 									      \
-	if (status == -EINTR)						      \
+	if (status == EINTR)						      \
 	  result = EINTR;						      \
-	else if (status == -ETIMEDOUT)					      \
+	else if (status == ETIMEDOUT)					      \
 	  result = EAGAIN;						      \
 	else								      \
-	  assert (status == 0 || status == -EWOULDBLOCK);		      \
+	  assert (status == 0 || status == EAGAIN);			      \
 									      \
 	pthread_mutex_lock (&__gai_requests_mutex);			      \
       }									      \