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powerpc: Fix write-after-destroy in lock elision [BZ #20822]

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The update of *adapt_count after the release of the lock causes a race
condition when thread A unlocks, thread B continues and destroys the
mutex, and thread A writes to *adapt_count.
This commit is contained in:
Tulio Magno Quites Machado Filho
2017-01-03 17:16:02 -02:00
parent daaff5cc79
commit e9a96ea1ac
4 changed files with 33 additions and 12 deletions
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10
sysdeps/unix/sysv/linux/powerpc/elision-lock.c
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@ -45,7 +45,9 @@
int
__lll_lock_elision (int *lock, short *adapt_count, EXTRAARG int pshared)
{
if (*adapt_count > 0)
/* adapt_count is accessed concurrently but is just a hint. Thus,
use atomic accesses but relaxed MO is sufficient. */
if (atomic_load_relaxed (adapt_count) > 0)
{
goto use_lock;
}
@ -67,7 +69,8 @@ __lll_lock_elision (int *lock, short *adapt_count, EXTRAARG int pshared)
if (_TEXASRU_FAILURE_PERSISTENT (__builtin_get_texasru ()))
{
if (aconf.skip_lock_internal_abort > 0)
*adapt_count = aconf.skip_lock_internal_abort;
atomic_store_relaxed (adapt_count,
aconf.skip_lock_internal_abort);
goto use_lock;
}
}
@ -75,7 +78,8 @@ __lll_lock_elision (int *lock, short *adapt_count, EXTRAARG int pshared)
/* Fall back to locks for a bit if retries have been exhausted */
if (aconf.try_tbegin > 0 && aconf.skip_lock_out_of_tbegin_retries > 0)
*adapt_count = aconf.skip_lock_out_of_tbegin_retries;
atomic_store_relaxed (adapt_count,
aconf.skip_lock_out_of_tbegin_retries);
use_lock:
return LLL_LOCK ((*lock), pshared);