Re: [PATCH RT] rt: Make cpu_chill() use hrtimer instead of msleep()

From: Sebastian Andrzej Siewior
Date: Fri Feb 07 2014 - 09:22:00 EST

On 02/07/2014 03:13 PM, Steven Rostedt wrote:
> On Fri, 7 Feb 2014 09:08:34 -0500
> Steven Rostedt <rostedt@xxxxxxxxxxx> wrote:
>>> could you please tell me which two locks are invovled here?
> I should have also stated that it was only one lock that was involved.
> But the lock owner was doing a msleep() that requires a wakeup by
> ksoftirqd to continue. If ksoftirqd happens to be blocked on a lock
> held by the msleep() caller, then you have your deadlock.

That makes sense.

> It's best not to have any softirqs going to sleep requiring another
> softirq to wake it up. Note, if we ever require a timer softirq to do a
> cpu_chill() it will most definitely hit this deadlock.

Yes. And that sleep in softirq is also not really nice but this isn't
new. Thanks for the patch & explanation.
> -- Steve

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