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Date: Tue, 23 Sep 2014 16:20:37 +0200
From: Peter Zijlstra <peterz@infradead.org>
To: Rik van Riel <riel@redhat.com>
Cc: Steven Rostedt <rostedt@goodmis.org>, Oleg Nesterov <oleg@redhat.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
        Thomas Gleixner <tglx@linutronix.de>, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 1/2] signal: simplify deadlock-avoidance in
 lock_task_sighand()
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On Tue, Sep 23, 2014 at 07:45:22AM -0400, Rik van Riel wrote:

> > 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.

But with CONFIG_PREEMPT we get preemptible RCU but not the
spinlock->rt_mutex conversion.