linux-kernel - Re: perf/tracepoint: another fuzzer generated lockup

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Message-ID: <20131109155938.GC4971@laptop.programming.kicks-ass.net>
Date:	Sat, 9 Nov 2013 16:59:38 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	Vince Weaver <vincent.weaver@...ne.edu>,
	Steven Rostedt <rostedt@...dmis.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...nel.org>, Dave Jones <davej@...hat.com>
Subject: Re: perf/tracepoint: another fuzzer generated lockup

On Sat, Nov 09, 2013 at 04:27:01PM +0100, Frederic Weisbecker wrote:
> In fact, raising an irq work from an irq work should simply be prohibited. That's not a sane
> behaviour.

Well, it is because as you raised on IRC we could be holding locks and
trying to avoid deadlocks. This is the very reason irq_work gets used in
printk.

And its not a recursive run()->work()->queue() either, because as you said this
tracepoint is in arch code _after_ work_run completes.

All in all an exceedingly vexing issue.
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