linux-kernel - Re: rcu, sched: WARNING: CPU: 30 PID: 23771 at kernel/rcu/tree_plugin.h:337 rcu_read_unlock

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Message-ID: <54C1BFFD.9060707@oracle.com>
Date:	Thu, 22 Jan 2015 22:29:01 -0500
From:	Sasha Levin <sasha.levin@...cle.com>
To:	paulmck@...ux.vnet.ibm.com
CC:	Lai Jiangshan <laijs@...fujitsu.com>,
	Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	LKML <linux-kernel@...r.kernel.org>,
	"davej@...emonkey.org.uk >> Dave Jones" <davej@...emonkey.org.uk>
Subject: Re: rcu, sched: WARNING: CPU: 30 PID: 23771 at kernel/rcu/tree_plugin.h:337
 rcu_read_unlock_special+0x369/0x550()

On 01/21/2015 07:43 PM, Paul E. McKenney wrote:
> On Wed, Jan 21, 2015 at 10:44:57AM -0500, Sasha Levin wrote:
>> On 01/20/2015 09:57 PM, Paul E. McKenney wrote:
>>>>> So RCU believes that an RCU read-side critical section that ended within
>>>>>>> an interrupt handler (in this case, an hrtimer) somehow got preempted.
>>>>>>> Which is not supposed to happen.
>>>>>>>
>>>>>>> Do you have CONFIG_PROVE_RCU enabled?  If not, could you please enable it
>>>>>>> and retry?
>>>>>
>>>>> I did have CONFIG_PROVE_RCU, and didn't see anything else besides what I pasted here.
>>> OK, fair enough.  I do have a stack of RCU CPU stall-warning changes on
>>> their way in, please see v3.19-rc1..630181c4a915 in -rcu, which is at:
>>>
>>> git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu.git
>>>
>>> These handle the problems that Dave Jones, yourself, and a few others
>>> located this past December.  Could you please give them a spin?
>>
>> They seem to be a part of -next already, so this testing already includes them.
>>
>> I seem to be getting them about once a day, anything I can add to debug it?
> 
> Could you please try reproducing with the following patch?

Yes, and I've got mixed results. It reproduced, and all I got was:

[  717.645572] ===============================
[  717.645572] [ INFO: suspicious RCU usage. ]
[  717.645572] 3.19.0-rc5-next-20150121-sasha-00064-g3c37e35-dirty #1809 Tainted: G        W
[  717.645572] -------------------------------
[  717.645572] kernel/rcu/tree_plugin.h:337 rcu_read_unlock() from irq or softirq with blocking in critical section!!!
[  717.645572] !
[  717.645572]
[  717.645572] other info that might help us debug this:
[  717.645572]
[  717.645572]
[  717.645572] rcu_scheduler_active = 1, debug_locks = 1
[  717.645572] 3 locks held by trinity-c29/16497:
[  717.645572]  #0:  (&sb->s_type->i_mutex_key){+.+.+.}, at: [<ffffffff81bec373>] lookup_slow+0xd3/0x420
[  717.645572]  #1:
[hang]

So the rest of the locks/stack trace didn't get printed, nor the pr_alert() which
should follow that.

I've removed the lockdep call and will re-run it.


Thanks,
Sasha


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