linux-kernel - Re: [PATCH -tip 0/2] fix lock inversion in lockless sys

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Message-ID: <20140914092200.GQ346@worktop.programming.kicks-ass.net>
Date:	Sun, 14 Sep 2014 11:22:00 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	riel@...hat.com
Cc:	linux-kernel@...r.kernel.org, mingo@...nel.org, prarit@...hat.com,
	oleg@...hat.com, sgruszka@...hat.com
Subject: Re: [PATCH -tip 0/2] fix lock inversion in lockless sys_times()

On Fri, Sep 12, 2014 at 09:12:13AM -0400, riel@...hat.com wrote:
> The sig->stats_lock nests inside the tasklist_lock and the
> sighand->siglock in __exit_signal and wait_task_zombie.
> 
> However, both of those locks can be taken from irq context,
> which means we need to use the interrupt safe variant of
> read_seqbegin_or_lock. This blocks interrupts when the "lock"
> branch is taken (seq is odd), preventing the lock inversion.
> 
> On the first (lockless) pass through the loop, irqs are not
> blocked.
> 
> This fixes the lockdep complaints that Stanislaw reported.
> 

Thanks Rik
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