Date: Tue, 9 Nov 2004 13:45:53 +0100
From: Ingo Molnar <mingo@elte.hu>
To: Oleg Nesterov <oleg@tv-sign.ru>
Cc: linux-kernel@vger.kernel.org, Andrew Morton <akpm@osdl.org>
Subject: Re: [PATCH] little schedule() cleanup: use cached current value
Message-ID: <20041109124553.GA25663@elte.hu>
References: <4190ADD7.CE7EFB7C@tv-sign.ru>
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* Oleg Nesterov <oleg@tv-sign.ru> wrote:

> @@ -2636,7 +2636,7 @@ switch_tasks:
>  	} else
>  		spin_unlock_irq(&rq->lock);
>  
> -	reacquire_kernel_lock(current);
> +	reacquire_kernel_lock(next);
>  	preempt_enable_no_resched();
>  	if (unlikely(test_thread_flag(TIF_NEED_RESCHED)))
>  		goto need_resched;

nack. We switch the kernel stack in switch_to() so 'next' here is the
old task we switched to before we went off the CPU. The value of 'next'
doesnt get carried over a context-switch. (we do carry 'prev' over via
assembly trickery because we need it, but not 'next'.) This change would
most likely result in rare, hard-to-track-down BKL-related crashes all
around the place.

the other bits are OK, please resend them.

	Ingo
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