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

[Jeffrey Hugo]

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@xxxxxxxxxxxxxx>

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.