linux-kernel - Re: [PATCH RFC] rtmutex: Permit rt_mutex_unlock() to be invoked with irqs disabled

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Message-ID: <1311247968.29152.122.camel@twins>
Date:	Thu, 21 Jul 2011 13:32:48 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	paulmck@...ux.vnet.ibm.com
Cc:	tglx@...utronix.de, laijs@...fujitsu.com, darren@...art.com,
	rostedt@...dmis.org, mingo@...e.hu, linux-kernel@...r.kernel.org
Subject: Re: [PATCH RFC] rtmutex: Permit rt_mutex_unlock() to be invoked
 with irqs disabled

On Tue, 2011-07-19 at 13:14 -0700, Paul E. McKenney wrote:
> Because rcu_read_unlock() can be invoked with interrupts disabled, it can
> in turn invoke rt_mutex_unlock() with interrupts disabled.  This situation
> results in lockdep splats (https://lkml.org/lkml/2011/7/7/362) because the
> rt_mutex structure's ->lock_wait is acquired elsewhere without disabling
> interrupts, which can result in deadlocks.
> 
> This commit therefore changes the rt_mutex structure's ->lock_wait
> acquisitions to disable interrupts.
> 
> An alternative fix is to prohibit invoking rcu_read_unlock() with
> interrupts disabled unless the entire preceding RCU read-side critical
> section has run with interrupts disabled.  However, there is already
> at least one case in mainline where this potential rule is violated,
> and there might well be many more.  These would likely be found one at
> a time using the lockdep-water-torture method, hence the alternative
> fix in the form of this commit.

Thomas, I'm inclined to merge this, any objections?
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