[dm-devel] Fix "dm kcopyd: Fix bug causing workqueue stalls" causes dead lock

[Guruswamy Basavaiah]

Hello Mike,
 I will get the testing result before end of Thursday.
Guru

On Wed, 9 Oct 2019 at 21:34, Mike Snitzer <snitzer at redhat.com> wrote:
>
> On Wed, Oct 09 2019 at 11:44am -0400,
> Nikos Tsironis <ntsironis at arrikto.com> wrote:
>
> > On 10/9/19 5:13 PM, Mike Snitzer wrote:> On Tue, Oct 01 2019 at  8:43am -0400,
> > > Nikos Tsironis <ntsironis at arrikto.com> wrote:
> > >
> > >> On 10/1/19 3:27 PM, Guruswamy Basavaiah wrote:
> > >>> Hello Nikos,
> > >>>  Yes, issue is consistently reproducible with us, in a particular
> > >>> set-up and test case.
> > >>>  I will get the access to set-up next week, will try to test and let
> > >>> you know the results before end of next week.
> > >>>
> > >>
> > >> That sounds great!
> > >>
> > >> Thanks a lot,
> > >> Nikos
> > >
> > > Hi Guru,
> > >
> > > Any chance you could try this fix that I've staged to send to Linus?
> > > https://git.kernel.org/pub/scm/linux/kernel/git/device-mapper/linux-dm.git/commit/?h=dm-5.4&id=633b1613b2a49304743c18314bb6e6465c21fd8a
> > >
> > > Shiort of that, Nikos: do you happen to have a test scenario that teases
> > > out this deadlock?
> > >
> >
> > Hi Mike,
> >
> > Yes,
> >
> > I created a 50G LV and took a snapshot of the same size:
> >
> >   lvcreate -n data-lv -L50G testvg
> >   lvcreate -n snap-lv -L50G -s testvg/data-lv
> >
> > Then I ran the following fio job:
> >
> > [global]
> > randrepeat=1
> > ioengine=libaio
> > bs=1M
> > size=6G
> > offset_increment=6G
> > numjobs=8
> > direct=1
> > iodepth=32
> > group_reporting
> > filename=/dev/testvg/data-lv
> >
> > [test]
> > rw=write
> > timeout=180
> >
> > , concurrently with the following script:
> >
> > lvcreate -n dummy-lv -L1G testvg
> >
> > while true
> > do
> >  lvcreate -n dummy-snap -L1M -s testvg/dummy-lv
> >  lvremove -f testvg/dummy-snap
> > done
> >
> > This reproduced the deadlock for me. I also ran 'echo 30 >
> > /proc/sys/kernel/hung_task_timeout_secs', to reduce the hung task
> > timeout.
> >
> > Nikos.
>
> Very nice, well done.  Curious if you've tested with the fix I've staged
> (see above)?  If so, does it resolve the deadlock?  If you've had
> success I'd be happy to update the tags in the commit header to include
> your Tested-by before sending it to Linus.  Also, any review of the
> patch that you can do would be appreciated and with your formal
> Reviewed-by reply would be welcomed and folded in too.
>
> Mike



-- 
Guruswamy Basavaiah