On Fri, Mar 29, 2013 at 6:55 AM, Rik van Riel <r...@surriel.com> wrote: > On Thu, 28 Mar 2013 19:50:47 -0700 > Michel Lespinasse <wal...@google.com> wrote: > >> This is IMO where the spin_unlock_wait(&sma->sem_perm.lock) would >> belong - right before the goto again. > > Here is the slightly more optimistic (and probably more readable) > version of the patch: > > ---8<--- > Unfortunately the locking scheme originally proposed has false positives > with lockdep. This can be fixed by changing the code to only ever take > one lock, and making sure that other relevant locks are not locked, before > entering a critical section. > > For the "global lock" case, this is done by taking the sem_array lock, > and then (potentially) waiting for all the semaphore's spinlocks to be > unlocked. > > For the "local lock" case, we wait on the sem_array's lock to be free, > before taking the semaphore local lock. To prevent races, we need to > check again after we have taken the local lock. > > Suggested-by: Peter Zijlstra <pet...@infradead.org> > Reported-by: Sasha Levin <sasha.le...@oracle.com> > Signed-off-by: Rik van Riel <r...@redhat.com>
Looks good. Reviewed-by: Michel Lespinasse <wal...@google.com> -- Michel "Walken" Lespinasse A program is never fully debugged until the last user dies. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
