Messages in this thread | | | Date | Fri, 11 Dec 2015 14:06:49 +0000 | From | Will Deacon <> | Subject | Re: FW: Commit 81a43adae3b9 (locking/mutex: Use acquire/release semantics) causing failures on arm64 (ThunderX) |
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On Fri, Dec 11, 2015 at 02:48:03PM +0100, Peter Zijlstra wrote: > On Fri, Dec 11, 2015 at 01:33:14PM +0000, Will Deacon wrote: > > On Fri, Dec 11, 2015 at 01:26:47PM +0100, Peter Zijlstra wrote: > > > > While we're there, the acquire in osq_wait_next() seems somewhat ill > > > documented too. > > > > > > I _think_ we need ACQUIRE semantics there because we want to strictly > > > order the lock-unqueue A,B,C steps and we get that with: > > > > > > A: SC > > > B: ACQ > > > C: Relaxed > > > > > > Similarly for unlock we want the WRITE_ONCE to happen after > > > osq_wait_next, but in that case we can even rely on the control > > > dependency there. > > > > Even for the lock-unqueue case, isn't B->C ordered by a control dependency > > because C consists only of stores? > > Hmm, indeed. So we could go fully relaxed on it I suppose, since the > same is true for the unlock site.
In which case, we should be able to relax the xchg in there (osq_wait_next) too, right?
Will
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