linux-kernel - Re: rcu_preempt detected stalls.

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Message-ID: <20141023183917.GX4977@linux.vnet.ibm.com>
Date:	Thu, 23 Oct 2014 11:39:17 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Sasha Levin <sasha.levin@...cle.com>
Cc:	Dave Jones <davej@...hat.com>,
	Linux Kernel <linux-kernel@...r.kernel.org>, htejun@...il.com
Subject: Re: rcu_preempt detected stalls.

On Tue, Oct 14, 2014 at 10:35:10PM -0400, Sasha Levin wrote:
> On 10/13/2014 01:35 PM, Dave Jones wrote:
> > oday in "rcu stall while fuzzing" news:
> > 
> > INFO: rcu_preempt detected stalls on CPUs/tasks:
> > 	Tasks blocked on level-0 rcu_node (CPUs 0-3): P766 P646
> > 	Tasks blocked on level-0 rcu_node (CPUs 0-3): P766 P646
> > 	(detected by 0, t=6502 jiffies, g=75434, c=75433, q=0)
> 
> I've complained about RCU stalls couple days ago (in a different context)
> on -next. I guess whatever causing them made it into Linus's tree?
> 
> https://lkml.org/lkml/2014/10/11/64

And on that one, I must confess that I don't see where the RCU read-side
critical section might be.

Hmmm...  Maybe someone forgot to put an rcu_read_unlock() somewhere.
Can you reproduce this with CONFIG_PROVE_RCU=y?

							Thanx, Paul

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