linux-kernel - Re: [PATCH 1/2] sched: Move __task_rq_{, un}lock() to kernel/sched/sched.h

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Date:	Tue, 17 Feb 2015 12:26:16 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Kirill Tkhai <ktkhai@...allels.com>
Cc:	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
	Josh Poimboeuf <jpoimboe@...hat.com>
Subject: Re: [PATCH 1/2] sched: Move __task_rq_{, un}lock() to
 kernel/sched/sched.h

On Tue, Feb 17, 2015 at 12:11:16PM +0100, Peter Zijlstra wrote:
> On Tue, Feb 17, 2015 at 01:46:51PM +0300, Kirill Tkhai wrote:
> > 
> > Place it in sched.h, because dl_task_timer() needs it.
> > Also remove lockdep check, which is not fit to this
> > function.
> 
> No, that lockdep check is valid for all current sites.

Also, note that you just proved the reason we didn't have pi_lock there
wrong the other day.

As per 0f397f2c90ce ("sched/dl: Fix race in dl_task_timer()"):

       "The only reason we don't strictly need ->pi_lock now is because
        we're guaranteed to have p->state == TASK_RUNNING here and are
        thus free of ttwu races".

And therefore we should use the full task_rq_lock() here.


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