[PATCH] powerpc: irq work racing with timer interrupt can result in timer interrupt hang
benh at kernel.crashing.org
Sun May 11 18:37:57 EST 2014
On Sun, 2014-05-11 at 13:45 +0530, Preeti U Murthy wrote:
> + /* Don't adjust the decrementer if some irq work is pending
> + if (!test_irq_work_pending())
> + set_dec(evt);
> + else
> + set_dec(1);
> ^^^^^ your patch currently does not have this
> set_dec(1) here. Will that create a problem?
> If there is any irq work pending at this point, will someone set the
> decrementer to fire immediately after this point? The current code in
> decrementer_set_next_event() sets set_dec(1) explicitly in case of
> pending irq work.
Hrm, actually this is an interesting point. The problem isn't that
*someone* will do a set_dec, nobody else should that matters.
The problem is that irq_work can be triggered typically by NMIs or
similar, which means that it might be queued between the
test_irq_work_pending() and the set_dec(), thus causing a race.
So basically Anton's original patch is fine :-) I had missed that
we did a post-set_dec() test already in decrementer_next_event()
so as far as I can tell, removing the pre-test, which is what Anton
does, is really all we need.
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