linux-kernel - Re: [PATCH tip/sched/urgent] sched: revert 498657a478c60be092208422fefa9c7b248729c2

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Message-ID: <4B13A8C3.3010605@redhat.com>
Date:	Mon, 30 Nov 2009 13:13:07 +0200
From:	Avi Kivity <avi@...hat.com>
To:	Tejun Heo <tj@...nel.org>
CC:	Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <peterz@...radead.org>,
	Jiri Slaby <jirislaby@...il.com>, linux-kernel@...r.kernel.org,
	akpm@...ux-foundation.org, mm-commits@...r.kernel.org,
	Marcelo Tosatti <mtosatti@...hat.com>, kvm@...r.kernel.org,
	the arch/x86 maintainers <x86@...nel.org>
Subject: Re: [PATCH tip/sched/urgent] sched: revert 498657a478c60be092208422fefa9c7b248729c2

On 11/30/2009 01:02 PM, Tejun Heo wrote:
> 498657a478c60be092208422fefa9c7b248729c2 incorrectly assumed that
> preempt wasn't disabled around context_switch() and thus was fixing
> imaginary problem.  It also broke kvm because it depended on
> ->sched_in() to be called with irq enabled so that it can do smp calls
> from there.
>
> Revert the incorrect commit and add comment describing different
> contexts under with the two callbacks are invoked.
>
>    *    notifier: struct preempt_notifier for the task being preempted
>    *    next: the task that's kicking us out
> + *
> + * Please note that sched_in and out are called under different
> + * contexts.  sched_in is called with rq lock held and irq disabled
> + * while sched_out is called without rq lock and irq enabled.
>    */
>    

Is this transposed?  sched_in must be called with interrupts enabled for 
the kvm IPI to work.

-- 
error compiling committee.c: too many arguments to function

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