linux-kernel - Re: [PATCH 3/3] wait_task_inactive: don't use the dummy version when !SMP && PREEMPT

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Date:	Wed, 30 Jul 2008 22:13:20 +0400
From:	Oleg Nesterov <oleg@...sign.ru>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>,
	Roland McGrath <roland@...hat.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/3] wait_task_inactive: don't use the dummy version when !SMP && PREEMPT

On 07/30, Linus Torvalds wrote:
> 
> On Wed, 30 Jul 2008, Oleg Nesterov wrote:
> >
> > The patch looks monstrous because it moves the (unchanged) definition
> > of wait_task_inactive() outside of "#ifdef CONFIG_SMP", but it is quite
> > trivial.
> 
> Hmm. Doesn't this just deadlock in UP (PREEMPT) if wait_task_interactive() 
> is ever called from a no-preempt context? 

Given that it calls schedule_timeout_uninterruptible(), it can't be used
from the no-preempt context,

> And if that's never the case, the comment should be updated to reflect 
> that (right now it says that it's only invalid to call it with interrupts 
> disabled to avoid cross-IPI deadlocks).

Yes, I think this function is might_sleep(),

> Oh, and shouldn't it do a "yield()" instead of a cpu_relax() on UP?

I _think_ that rq->curr must be == current without CONFIG_SMP, but

> and I want to understand why it's 
> ok (_if_ it's ok).

me too.

Hopefully Ingo can ack/nack.

Oleg.

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