On Mon, May 05, 2014 at 05:34:08PM +0200, Frederic Weisbecker wrote: > On Mon, May 05, 2014 at 05:12:28PM +0200, Peter Zijlstra wrote: > > > Note the current ordering: > > > > > > cmpxchg(&qsd->pending, 0, 1) get ipi > > > csd_lock(qsd->csd) xchg(&qsd->pending, 1) > > > send ipi csd_unlock(qsd->csd) > > > > > > > > > So there shouldn't be racing updaters. Also ipi sender shouldn't > > > race with ipi receiver, the update shouldn't always eventually see > > > the unlock happening. > > > > Yeah, I've not spotted how this particular train wreck happens either. > > > > The problem is reproduction, it took me 9 hours to confirm I could > > reproduce the problem on my machine. So how long to I run it with this > > patch reverted to show its gone.. > > Maybe it could be favoured cpu hotplug. Anyway converting to irq_work should > fix it. Ingo needs a commit msg for the revert of this patch; do you think you have time to look into _why_ this patch is broken and write such a thing?
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