Messages in this thread | | | Date | Fri, 11 Dec 2015 14:48:03 +0100 | From | Peter Zijlstra <> | 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 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.
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