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Document a behavior of an elided pthread_rwlock_unlock

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Explain that pthread_rwlock_unlock may crash if called on a lock not
held by the current thread.
This commit is contained in:
Tulio Magno Quites Machado Filho 2016-10-28 18:31:24 -02:00
parent ce193f551e
commit 739e14f900
3 changed files with 13 additions and 0 deletions
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6
ChangeLog
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@ -1,3 +1,9 @@
2016-10-28 Tulio Magno Quites Machado Filho <tuliom@linux.vnet.ibm.com>
* nptl/pthread_rwlock_unlock.c: Add a comment explaining its
behavior when eliding a lock not held by the current thread.
* sysdeps/powerpc/nptl/elide.h: Likewise.
2016-10-28 Tulio Magno Quites Machado Filho <tuliom@linux.vnet.ibm.com> 2016-10-28 Tulio Magno Quites Machado Filho <tuliom@linux.vnet.ibm.com>
[BZ #20728] [BZ #20728]

4
nptl/pthread_rwlock_unlock.c
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@ -35,6 +35,10 @@ __pthread_rwlock_unlock (pthread_rwlock_t *rwlock)
LIBC_PROBE (rwlock_unlock, 1, rwlock); 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 if (ELIDE_UNLOCK (rwlock->__data.__writer == 0
&& rwlock->__data.__nr_readers == 0)) && rwlock->__data.__nr_readers == 0))
return 0; return 0;

3
sysdeps/powerpc/nptl/elide.h
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@ -102,6 +102,9 @@ __elide_unlock (int is_lock_free)
{ {
if (is_lock_free) if (is_lock_free)
{ {
/* This code is expected to crash when trying to unlock a lock not
held by this thread. More information is available in the
__pthread_rwlock_unlock() implementation. */
__libc_tend (0); __libc_tend (0);
return true; return true;
} }