linux-kernel - Re: [PATCH] Fix posix-cpu-timer breakage caused by stale p->last

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Message-ID: <20070222074624.GA9800@elte.hu>
Date:	Thu, 22 Feb 2007 08:46:24 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	john stultz <johnstul@...ibm.com>,
	Roman Zippel <zippel@...ux-m68k.org>,
	Mike Galbraith <efault@....de>,
	Ken Chen <kenneth.w.chen@...el.com>, balducci@...ts.it,
	LKML <linux-kernel@...r.kernel.org>, Greg KH <greg@...ah.com>
Subject: Re: [PATCH] Fix posix-cpu-timer breakage caused by stale p->last_ran value


* Thomas Gleixner <tglx@...utronix.de> wrote:

> The problem is that the p->last_ran value is not updated after a 
> context switch. So a subsequent call to current_sched_time() 
> calculates with a stale p->last_ran value, i.e. accounts the full 
> time, which the task was scheduled away.
> 
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>

>  	sched_info_switch(prev, next);
>  	if (likely(prev != next)) {
> -		next->timestamp = now;
> +		next->timestamp = next->last_ran = now;

ouch! nice catch. Also for v2.6.20.2 i think. 2.6.19 should be 
unaffected.

Acked-by: Ingo Molnar <mingo@...e.hu>

	Ingo
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