Fix semaphore destruction (bug 12674).

This commit fixes semaphore destruction by either using 64b atomic
operations (where available), or by using two separate fields when only
32b atomic operations are available.  In the latter case, we keep a
conservative estimate of whether there are any waiting threads in one
bit of the field that counts the number of available tokens, thus
allowing sem_post to atomically both add a token and determine whether
it needs to call futex_wake.

See:
https://sourceware.org/ml/libc-alpha/2014-12/msg00155.html

1 files changed, 8 insertions, 88 deletions

diff --git a/nptl/sem_timedwait.c b/nptl/sem_timedwait.c
index d04bcdf38b..042b0acd58 100644
--- a/nptl/sem_timedwait.c
+++ b/nptl/sem_timedwait.c
@@ -1,4 +1,4 @@
-/* sem_timedwait -- wait on a semaphore.  Generic futex-using version.
+/* sem_timedwait -- wait on a semaphore with timeout.
    Copyright (C) 2003-2015 Free Software Foundation, Inc.
    This file is part of the GNU C Library.
    Contributed by Paul Mackerras <paulus@au.ibm.com>, 2003.
@@ -17,101 +17,21 @@
    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 <internaltypes.h>
-#include <semaphore.h>
-#include <sys/time.h>
-
-#include <pthreadP.h>
-#include <shlib-compat.h>
-
-
-extern void __sem_wait_cleanup (void *arg) attribute_hidden;
-
-/* This is in a seperate function in order to make sure gcc
-   puts the call site into an exception region, and thus the
-   cleanups get properly run.  */
-static int
-__attribute__ ((noinline))
-do_futex_timed_wait (struct new_sem *isem, struct timespec *rt)
-{
-  int err, oldtype = __pthread_enable_asynccancel ();
-
-  err = lll_futex_timed_wait (&isem->value, 0, rt,
-			      isem->private ^ FUTEX_PRIVATE_FLAG);
-
-  __pthread_disable_asynccancel (oldtype);
-  return err;
-}
+#include "sem_waitcommon.c"
 
+/* This is in a separate file because because sem_timedwait is only provided
+   if __USE_XOPEN2K is defined.  */
 int
 sem_timedwait (sem_t *sem, const struct timespec *abstime)
 {
-  struct new_sem *isem = (struct new_sem *) sem;
-  int err;
-
-  if (atomic_decrement_if_positive (&isem->value) > 0)
-    return 0;
-
   if (abstime->tv_nsec < 0 || abstime->tv_nsec >= 1000000000)
     {
       __set_errno (EINVAL);
       return -1;
     }
 
-  atomic_increment (&isem->nwaiters);
-
-  pthread_cleanup_push (__sem_wait_cleanup, isem);
-
-  while (1)
-    {
-      struct timeval tv;
-      struct timespec rt;
-      int sec, nsec;
-
-      /* Get the current time.  */
-      __gettimeofday (&tv, NULL);
-
-      /* Compute relative timeout.  */
-      sec = abstime->tv_sec - tv.tv_sec;
-      nsec = abstime->tv_nsec - tv.tv_usec * 1000;
-      if (nsec < 0)
-	{
-	  nsec += 1000000000;
-	  --sec;
-	}
-
-      /* Already timed out?  */
-      if (sec < 0)
-	{
-	  __set_errno (ETIMEDOUT);
-	  err = -1;
-	  break;
-	}
-
-      /* Do wait.  */
-      rt.tv_sec = sec;
-      rt.tv_nsec = nsec;
-      err = do_futex_timed_wait(isem, &rt);
-      if (err != 0 && err != -EWOULDBLOCK)
-	{
-	  __set_errno (-err);
-	  err = -1;
-	  break;
-	}
-
-      if (atomic_decrement_if_positive (&isem->value) > 0)
-	{
-	  err = 0;
-	  break;
-	}
-    }
-
-  pthread_cleanup_pop (0);
-
-  atomic_decrement (&isem->nwaiters);
-
-  return err;
+  if (__new_sem_wait_fast ((struct new_sem *) sem, 0) == 0)
+    return 0;
+  else
+    return __new_sem_wait_slow((struct new_sem *) sem, abstime);
 }