linux-kernel - Re: 4.2-rc5 rcu stalls.

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Date:	Mon, 3 Aug 2015 17:55:35 -0400
From:	Dave Jones <davej@...emonkey.org.uk>
To:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:	Linux Kernel <linux-kernel@...r.kernel.org>,
	Josh Triplett <josh@...htriplett.org>, sasha.levin@...cle.com,
	fweisbec@...il.com
Subject: Re: 4.2-rc5 rcu stalls.

On Mon, Aug 03, 2015 at 02:37:23PM -0700, Paul E. McKenney wrote:
 > On Mon, Aug 03, 2015 at 05:08:35PM -0400, Dave Jones wrote:
 > > [ 2120.855128] 	Tasks blocked on level-0 rcu_node (CPUs 0-3): P1497
 > > [ 2120.855263] 	(detected by 2, t=65002 jiffies, g=78835, c=78834, q=0)
 > > [ 2120.855403] trinity-watchdo R  running task    14336  1497   1496 0x00080000
 > > [ 2120.855563]  ffff8804b94e3c88 ffffffffa17fa0b0 ffff8805010a1b40 ffff8804f58b51c0
 > > [ 2120.855728]  ffff8805010a1b40 ffff8804b94e3c78 0000000000000000 ffff8804b94e4000
 > > [ 2120.855893]  0000000000000001 0000000000000001 0000000000000002 ffff8804b94e3ca8
 > > [ 2120.856062] Call Trace:
 > > [ 2120.856116]  [<ffffffffa17fa0b0>] ? preempt_schedule_irq+0x40/0xa0
 > > [ 2120.856252]  [<ffffffffa17fa0b6>] preempt_schedule_irq+0x46/0xa0
 > 
 > Sasha Levin (CCed) was having roughly similar stalls, and found that
 > reverting b30f0e3ffedf (sched/preempt: Optimize preemption operations
 > on __schedule() callers) made the stalls go away.  Does that help in
 > your case?

Ugh, that doesn't revert cleanly.  Got something handy ?

The curious thing is why I've only just started seeing these.
I've had that machine for a month now, so it's been fuzzing since ~4.1,
and until yesterday I'd not seen this at all.

	Dave

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