linux-kernel - Re: [BUG] Deadlock due due to interactions of block, RCU, and cpu offline

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Message-ID: <d64c9d16-3b91-2081-0633-7f6a5196fd45@codeaurora.org>
Date:   Thu, 29 Jun 2017 10:29:12 -0600
From:   Jeffrey Hugo <jhugo@...eaurora.org>
To:     paulmck@...ux.vnet.ibm.com
Cc:     linux-kernel@...r.kernel.org, linux-block@...r.kernel.org,
        pprakash@...eaurora.org, Josh Triplett <josh@...htriplett.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        Jens Axboe <axboe@...nel.dk>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Richard Cochran <rcochran@...utronix.de>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Richard Weinberger <richard@....at>
Subject: Re: [BUG] Deadlock due due to interactions of block, RCU, and cpu
 offline

On 6/27/2017 6:11 PM, Paul E. McKenney wrote:
> On Tue, Jun 27, 2017 at 04:32:09PM -0600, Jeffrey Hugo wrote:
>> On 6/22/2017 9:34 PM, Paul E. McKenney wrote:
>>> On Wed, Jun 21, 2017 at 09:18:53AM -0700, Paul E. McKenney wrote:
>>>> No worries, and I am very much looking forward to seeing the results of
>>>> your testing.
>>>
>>> And please see below for an updated patch based on LKML review and
>>> more intensive testing.
>>>
>>
>> I spent some time on this today.  It didn't go as I expected.  I
>> validated the issue is reproducible as before on 4.11 and 4.12 rcs 1
>> through 4.  However, the version of stress-ng that I was using ran
>> into constant errors starting with rc5, making it nearly impossible
>> to make progress toward reproduction.  Upgrading stress-ng to tip
>> fixes the issue, however, I've still been unable to repro the issue.
>>
>> Its my unfounded suspicion that something went in between rc4 and
>> rc5 which changed the timing, and didn't actually fix the issue.  I
>> will run the test overnight for 5 hours to try to repro.
>>
>> The patch you sent appears to be based on linux-next, and appears to
>> have a number of dependencies which prevent it from cleanly applying
>> on anything current that I'm able to repro on at this time.  Do you
>> want to provide a rebased version of the patch which applies to say
>> 4.11?  I could easily test that and report back.
> 
> Here is a very lightly tested backport to v4.11.
> 

Works for me. Always reproduced the lockup within 2 minutes on stock 
4.11.  With the change applied, I was able to test for 2 hours in the 
same conditions, and 4 hours with the full system and not encounter an 
issue.

Feel free to add:
Tested-by: Jeffrey Hugo <jhugo@...eaurora.org>

I'm going to go back to 4.12-rc5 and see if I can get either repro the 
issue, or identify what changed.  Hopefully I can get to linux-next and 
double check the original version of the change as well.

-- 
Jeffrey Hugo
Qualcomm Datacenter Technologies as an affiliate of Qualcomm 
Technologies, Inc.
Qualcomm Technologies, Inc. is a member of the
Code Aurora Forum, a Linux Foundation Collaborative Project.