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Date: Fri, 29 Mar 2013 06:59:41 -0700 From: Michel Lespinasse <walken@...gle.com> To: Rik van Riel <riel@...riel.com> Cc: Peter Zijlstra <peterz@...radead.org>, Sasha Levin <sasha.levin@...cle.com>, torvalds@...ux-foundation.org, davidlohr.bueso@...com, linux-kernel@...r.kernel.org, akpm@...ux-foundation.org, hhuang@...hat.com, jason.low2@...com, lwoodman@...hat.com, chegu_vinod@...com, Dave Jones <davej@...hat.com>, benisty.e@...il.com, Ingo Molnar <mingo@...hat.com> Subject: Re: [PATCH v3 -mm -next] ipc,sem: fix lockdep false positive On Fri, Mar 29, 2013 at 6:55 AM, Rik van Riel <riel@...riel.com> wrote: > On Thu, 28 Mar 2013 19:50:47 -0700 > Michel Lespinasse <walken@...gle.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 <peterz@...radead.org> > Reported-by: Sasha Levin <sasha.levin@...cle.com> > Signed-off-by: Rik van Riel <riel@...hat.com> Looks good. Reviewed-by: Michel Lespinasse <walken@...gle.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 majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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