Messages in this thread | | | Subject | Re: [BUG] "sched: Remove rq->lock from the first half of ttwu()" locks up on ARM | From | Peter Zijlstra <> | Date | Thu, 26 May 2011 12:32:59 +0200 |
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On Thu, 2011-05-26 at 15:29 +0800, Yong Zhang wrote: > > Figuring out why the existing condition failed > > Seems 'current' will change before/after switch_to since it's derived from > sp register. > So that means if interrupt come before we switch sp, 'p == current' will > catch it, but if interrupt comes after we switch sp, we will lose a wake up.
Well, loosing a wakeup isn't the problem here (although it would be a problem), the immediate problem is that we're getting stuck (life-locked) in that while (p->on_cpu) loop.
But yes, I think that explains it, if the interrupts hits context_switch() after current was changed but before clearing p->on_cpu, we would life-lock in interrupt context.
Now we could of course go add in_interrupt() checks there, but that would make this already fragile path more interesting, so I think I'll stick with the proposed patch -- again provided it actually works.
Marc, any word on that?
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