linux-kernel - Re: [PATCH 1/2] signal: simplify deadlock-avoidance in lock_task

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Message-ID: <54215D52.8030201@redhat.com>
Date:	Tue, 23 Sep 2014 07:45:22 -0400
From:	Rik van Riel <riel@...hat.com>
To:	Steven Rostedt <rostedt@...dmis.org>,
	Oleg Nesterov <oleg@...hat.com>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] signal: simplify deadlock-avoidance in lock_task_sighand()

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On 09/22/2014 05:24 PM, Steven Rostedt wrote:
> On Mon, 22 Sep 2014 21:11:30 +0200 Oleg Nesterov <oleg@...hat.com>
> wrote:

>> so this patch doesn't try to change the rules.
>> 
>> But perhaps we can simply remove this preempt_disable/enable?
>> 
>> Or. We can shift rcu_read_unlock() from lock_task_sighand() to 
>> unlock_task_sighand(). This way we can avoid preempt_disable too,
>> but I'd prefer to not do this.
> 
> I really thing the preempt_disable/enable is not needed.
> 
> Paul, Thomas, care to comment?

I suspect you are right.  On normal kernels, rcu_read_lock() will
ensure preemption is disabled.

On -rt, the locks within are all sleepable mutexes.

Either way, things should be ok.

- -- 
All rights reversed
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