linux-kernel - Re: [sched] WARNING: CPU: 0 PID: 0 at kernel/time/hrtimer.c:802 hrtimer

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Message-ID: <20150501101007.GB5029@twins.programming.kicks-ass.net>
Date:	Fri, 1 May 2015 12:10:07 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Fengguang Wu <fengguang.wu@...el.com>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Ben Segall <bsegall@...gle.com>, LKP <lkp@...org>,
	linux-kernel@...r.kernel.org
Subject: Re: [sched] WARNING: CPU: 0 PID: 0 at kernel/time/hrtimer.c:802
 hrtimer_forward()

On Fri, May 01, 2015 at 12:47:13PM +0800, Fengguang Wu wrote:
> commit 77a4d1a1b9a122ca1fa3507bd30aec1520d7a8a4
>     sched: Cleanup bandwidth timers

> [   64.000438] WARNING: CPU: 0 PID: 0 at kernel/time/hrtimer.c:802 hrtimer_forward+0x71/0x189()

Argh, yes of course. The problem is that the timer can be re-started
before the handler acquires the lock, and therefore the hrtimer_forwards
in the handler will trigger that WARN.

Lemme try and go convince this heap of snot that's occupying my brain
cavity to produce coherent thought and come up with a nice fix for that.
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