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From: Frederic Weisbecker <fweisbec@gmail.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Vince Weaver <vincent.weaver@maine.edu>,
	Steven Rostedt <rostedt@goodmis.org>,
	LKML <linux-kernel@vger.kernel.org>,
	Ingo Molnar <mingo@kernel.org>, Dave Jones <davej@redhat.com>
Subject: Re: perf/tracepoint: another fuzzer generated lockup
Date: Sat, 9 Nov 2013 16:27:01 +0100	[thread overview]
Message-ID: <20131109152659.GD26079@localhost.localdomain> (raw)
In-Reply-To: <20131109151356.GA4971@laptop.programming.kicks-ass.net>

On Sat, Nov 09, 2013 at 04:13:56PM +0100, Peter Zijlstra wrote:
> On Sat, Nov 09, 2013 at 03:52:59PM +0100, Frederic Weisbecker wrote:
> > So, an idea of what may be happening: an event overflows while FASYNC flag is set so it triggers an irq work
> > to send the signal (kill_fasync).
> > After the irq work triggers, it generates an irq_work_exit event, which in turn overflows and,
> > if it has FASYNC, triggers a new irq work. The irq work triggers and generates an irq work exit event which
> > has FASYNC flag, etc...
> > 
> > Looks like a nice way to deadlock with an infinite loop of irq work.
> 
> 
> Yep, exactly, see the email I just send.

In fact, raising an irq work from an irq work should simply be prohibited. That's not a sane
behaviour.

It's natural for async stuffs that have reasonable delays between each pass allow re-enqueuing,
like workqueue or rcu callbacks, or timers. But with irq work that doesn't look right, expect for
lazy irq works though. But lets just not allow it at all :)

  reply	other threads:[~2013-11-09 15:27 UTC|newest]

Thread overview: 38+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2013-11-08 19:45 perf/tracepoint: another fuzzer generated lockup Vince Weaver
2013-11-08 20:06 ` Vince Weaver
2013-11-08 20:02   ` Frederic Weisbecker
2013-11-08 20:23     ` Vince Weaver
2013-11-08 20:48       ` Frederic Weisbecker
2013-11-08 21:15         ` Vince Weaver
2013-11-08 22:24           ` Frederic Weisbecker
2013-11-08 22:36           ` Frederic Weisbecker
2013-11-09  1:09             ` Steven Rostedt
2013-11-09 14:10             ` Peter Zijlstra
2013-11-09 14:20               ` Frederic Weisbecker
2013-11-11 12:44                 ` Ingo Molnar
2013-11-11 15:53                   ` Peter Zijlstra
2013-11-11 21:13                     ` Ingo Molnar
2013-11-09 14:52               ` Frederic Weisbecker
2013-11-09 15:13                 ` Peter Zijlstra
2013-11-09 15:27                   ` Frederic Weisbecker [this message]
2013-11-09 15:59                     ` Peter Zijlstra
2013-11-09 16:08                       ` Frederic Weisbecker
2013-11-09 15:11             ` Peter Zijlstra
2013-11-09 15:22               ` Frederic Weisbecker
2013-11-09 15:30                 ` Peter Zijlstra
2013-11-14 15:23               ` Peter Zijlstra
2013-11-14 15:33                 ` Peter Zijlstra
2013-11-14 15:35                   ` Frederic Weisbecker
2013-11-15  1:16                   ` Masami Hiramatsu
2013-11-15 12:28                     ` Peter Zijlstra
2013-11-15 14:15                       ` Steven Rostedt
2013-11-15 14:28                         ` Frederic Weisbecker
2013-11-17  7:53                           ` Masami Hiramatsu
2013-11-17  9:43                             ` Peter Zijlstra
2013-11-14 16:03                 ` Frederic Weisbecker
2013-11-14 17:20                 ` Vince Weaver
2013-11-14 17:14                   ` Peter Zijlstra
2013-11-14 17:41                     ` Steven Rostedt
2013-11-14 19:18                     ` Vince Weaver
2013-11-19 19:18                 ` [tip:perf/urgent] ftrace, perf: Avoid infinite event generation loop tip-bot for Peter Zijlstra
2013-11-09  0:25           ` perf/tracepoint: another fuzzer generated lockup Frederic Weisbecker

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