linux-kernel - Re: [PATCH] sched: reassign prev and switch_count when reacquire_kernel

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Date:	Tue, 12 Jan 2010 11:16:23 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Yong Zhang <yong.zhang0@...il.com>
Cc:	linux-kernel <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH] sched: reassign prev and switch_count when 
 reacquire_kernel_lock() fail

On Mon, 2010-01-11 at 14:38 +0800, Yong Zhang wrote:
> From 4c04fbbd43f3fef7a3b9471a0000c399c2e045ed Mon Sep 17 00:00:00 2001
> From: Yong Zhang <yong.zhang0@...il.com>
> Date: Mon, 11 Jan 2010 14:21:25 +0800
> Subject: [PATCH] sched: reassign prev and switch_count when
> reacquire_kernel_lock() fail
> 
> Assume A->B schedule is processing, if B have acquired BKL before and
> it need reschedule this time. Then on B's context, it will go to
> need_resched_nonpreemptible for reschedule. But at this time, prev
> and switch_count are related to A. It's wrong and will lead to
> incorrect scheduler statistics.
> 
> Signed-off-by: Yong Zhang <yong.zhang0@...il.com>

Looks good, picked it up, thanks!

> ---
>  kernel/sched.c |    5 ++++-
>  1 files changed, 4 insertions(+), 1 deletions(-)
> 
> diff --git a/kernel/sched.c b/kernel/sched.c
> index c535cc4..4508fe7 100644
> --- a/kernel/sched.c
> +++ b/kernel/sched.c
> @@ -5530,8 +5530,11 @@ need_resched_nonpreemptible:
> 
>  	post_schedule(rq);
> 
> -	if (unlikely(reacquire_kernel_lock(current) < 0))
> +	if (unlikely(reacquire_kernel_lock(current) < 0)) {
> +		prev = rq->curr;
> +		switch_count = &prev->nivcsw;
>  		goto need_resched_nonpreemptible;
> +	}
> 
>  	preempt_enable_no_resched();
>  	if (need_resched())


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