Messages in this thread | | | Date | Tue, 28 Apr 2015 18:24:58 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH 2/2] [PATCH] sched: Add smp_rmb() in task rq locking cycles |
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On Tue, Apr 28, 2015 at 11:53:21AM -0400, Chris Metcalf wrote: > As you surmise, tilepro doesn't have 64-bit loads. So we are stuck with > 32-bit loads on these two fields. It's true that spin_unlock_wait() can > therefore falsely claim that the lock is unlocked, but it should be only a > hint anyway, since by the time the caller tries to act on that information > the lock may have been retaken anyway, right? If spin_unlock_wait() is > really trying to guarantee that the lock was available at some point in > the interval between when it was called and when it returned, we could use > READ_ONCE() to read the current ticket value first; is that a necessary > part of the semantics?
I think it must not return before the lock holder that is current at the time of calling releases. Anything thereafter is indeed fair game as per your logic above.
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