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Date: Fri, 12 Dec 2014 13:42:48 -0500
From: Dave Jones <davej@redhat.com>
To: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>, Chris Mason <clm@fb.com>,
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        =?iso-8859-1?Q?D=E2niel?= Fraga <fragabr@gmail.com>,
        Sasha Levin <sasha.levin@oracle.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: frequent lockups in 3.18rc4
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On Fri, Dec 12, 2014 at 10:10:44AM -0800, Paul E. McKenney wrote:

 > > [18801.941908] INFO: rcu_preempt detected stalls on CPUs/tasks:
 > > [18801.942920] 	3: (3 GPs behind) idle=bf4/0/0 softirq=1597256/1597257 
 > > [18801.943890] 	(detected by 0, t=6002 jiffies, g=763359, c=763358, q=0)
 > > [18801.944843] Task dump for CPU 3:
 > > [18801.945770] swapper/3       R  running task    14576     0      1 0x00200000
 > > [18801.946706]  0000000342b6fe28 def23185c07e1b3d ffffe8ffff403518 0000000000000001
 > > [18801.947629]  ffffffff81cb2000 0000000000000003 ffff880242b6fe78 ffffffff8166cb95
 > > [18801.948557]  0000111242adb59f ffffffff81cb2070 ffff880242b6c000 ffffffff81d21ab0
 > > [18801.949478] Call Trace:
 > > [18801.950384]  [<ffffffff8166cb95>] ? cpuidle_enter_state+0x55/0x1c0
 > > [18801.951303]  [<ffffffff8166cdb7>] ? cpuidle_enter+0x17/0x20
 > > [18801.952211]  [<ffffffff810bf303>] ? cpu_startup_entry+0x423/0x4d0
 > > [18801.953125]  [<ffffffff810314c3>] ? start_secondary+0x1a3/0x220
 > 
 > Very strange.  Both cpuidle_enter() and cpuidle_enter_state() should be
 > within the idle loop, so that RCU should be ignoring this CPU.  And the
 > "idle=bf4/0/0" means that it really has marked itself as being idle from
 > an RCU perspective.  So I am guessing that the RCU grace-period kthread
 > has not gotten a chance to run.
 > 
 > If you are willing to live a bit dangerously, could you please see if
 > the (not for mainline) patch below clears this up?

I'll try anything at this point, regardless of danger level :)

	Dave

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