linux-kernel - Re: [PATCH rcu/urgent 0/6] Fixes for RCU/scheduler/irq-threads trainwreck

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Date:	Wed, 20 Jul 2011 21:25:46 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	paulmck@...ux.vnet.ibm.com
Cc:	Ingo Molnar <mingo@...e.hu>, Ben Greear <greearb@...delatech.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ed Tomlinson <edt@....ca>, linux-kernel@...r.kernel.org,
	laijs@...fujitsu.com, dipankar@...ibm.com,
	akpm@...ux-foundation.org, mathieu.desnoyers@...ymtl.ca,
	josh@...htriplett.org, niv@...ibm.com, tglx@...utronix.de,
	rostedt@...dmis.org, Valdis.Kletnieks@...edu, dhowells@...hat.com,
	eric.dumazet@...il.com, darren@...art.com, patches@...aro.org,
	edward.tomlinson@...o.bombardier.com
Subject: Re: [PATCH rcu/urgent 0/6] Fixes for RCU/scheduler/irq-threads
 trainwreck

On Wed, 2011-07-20 at 12:01 -0700, Paul E. McKenney wrote:
>   This can interact badly with the recently
> added RCU read-side critical sections in the scheduler that have
> either the runqueue or the priority-inheritance locks held, especially
> when interrupts occur towards the end of __rcu_read_unlock(). 

Right, so while I recently added a lot more, there have been rcu usage
sites under rq->lock for a long while, see commits

a18b83b7ef ("cpuacct: make cpuacct hierarchy walk in cpuacct_charge()
safe when rcupreempt is used -v2") -- March 2009.

f3b577dec1 ("rcu: apply RCU protection to wake_affine()") -- Jun 2010

b0a0f667 ("sched: suppress RCU lockdep splat in task_fork_fair") -- Oct
2010

So I'm not quite seeing how the problems we're hitting now are new.
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