This is the mail archive of the
gcc-bugs@gcc.gnu.org
mailing list for the GCC project.
[Bug libgomp/50175] data race with OMP barrier
- From: "jakub at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>
- To: gcc-bugs at gcc dot gnu dot org
- Date: Wed, 24 Aug 2011 14:55:18 +0000
- Subject: [Bug libgomp/50175] data race with OMP barrier
- Auto-submitted: auto-generated
- References: <bug-50175-4@http.gcc.gnu.org/bugzilla/>
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50175
Jakub Jelinek <jakub at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |jakub at gcc dot gnu.org,
| |rth at gcc dot gnu.org
--- Comment #1 from Jakub Jelinek <jakub at gcc dot gnu.org> 2011-08-24 14:55:18 UTC ---
If this is about bar->arrived writes, then I don't see any races.
During the lifetime of a barrier, in the first phase arrived is incremented by
each thread, guarded by bar->mutex1 lock. The threads then unlock bar->mutex1
lock, except for the last thread which keeps it locked and decrements
bar->arrived again, then, still with bar->mutex1 locked wakes up all the other
threads which then either atomically, or guarded with bar->mutex2 lock,
decrement bar->arrived again. The last of those threads then posts to
bar->sem2
semaphore on which the thread holding bar->mutex1 is waiting before unlocking
that lock. Thus, I don't see how the first phase (where bar->arrived
adjustments are done guarded with bar->mutex1 lock) can overlap with the second
phase (where it is decremented atomically or with mutex2). Not even the second
phase with following first phase. Thus I think valgrind is wrong about this.
CCing rth as author...