Re: REGRESSION: 37f4a24c2469: blk-mq: centralise related handling into blk_mq_get_driver_tag

[Shakeel Butt]

On Fri, Sep 25, 2020 at 9:32 AM Shakeel Butt <shakeelb@xxxxxxxxxx> wrote:
>
> On Fri, Sep 25, 2020 at 9:19 AM Ming Lei <ming.lei@xxxxxxxxxx> wrote:
> >
> > On Fri, Sep 25, 2020 at 03:31:45PM +0800, Ming Lei wrote:
> > > On Thu, Sep 24, 2020 at 09:13:11PM -0400, Theodore Y. Ts'o wrote:
> > > > On Thu, Sep 24, 2020 at 10:33:45AM -0400, Theodore Y. Ts'o wrote:
> > > > > HOWEVER, thanks to a hint from a colleague at $WORK, and realizing
> > > > > that one of the stack traces had virtio balloon in the trace, I
> > > > > realized that when I switched the GCE VM type from e1-standard-2 to
> > > > > n1-standard-2 (where e1 VM's are cheaper because they use
> > > > > virtio-balloon to better manage host OS memory utilization), problem
> > > > > has become, much, *much* rarer (and possibly has gone away, although
> > > > > I'm going to want to run a lot more tests before I say that
> > > > > conclusively) on my test setup.  At the very least, using an n1 VM
> > > > > (which doesn't have virtio-balloon enabled in the hypervisor) is
> > > > > enough to unblock ext4 development.
> > > >
> > > > .... and I spoke too soon.  A number of runs using -rc6 are now
> > > > failing even with the n1-standard-2 VM, so virtio-ballon may not be an
> > > > indicator.
> > > >
> > > > This is why debugging this is frustrating; it is very much a heisenbug
> > > > --- although 5.8 seems to work completely reliably, as does commits
> > > > before 37f4a24c2469.  Anything after that point will show random
> > > > failures.  :-(
> > >
> > > It does not make sense to mention 37f4a24c2469, which is reverted in
> > > 4e2f62e566b5. Later the patch in 37f4a24c2469 is fixed and re-commited
> > > as 568f27006577.
> > >
> > > However, I can _not_ reproduce the issue by running the same test on
> > > kernel built from 568f27006577 directly.
> > >
> > > Also you have confirmed that the issue can't be fixed after reverting
> > > 568f27006577 against v5.9-rc4.
> > >
> > > Looks the real issue(slab list corruption) should be introduced between
> > > 568f27006577 and v5.9-rc4.
> >
> > git bisect shows the first bad commit:
> >
> >         [10befea91b61c4e2c2d1df06a2e978d182fcf792] mm: memcg/slab: use a single set of
> >                 kmem_caches for all allocations
> >
> > And I have double checked that the above commit is really the first bad
> > commit for the list corruption issue of 'list_del corruption, ffffe1c241b00408->next
> > is LIST_POISON1 (dead000000000100)', see the detailed stack trace and
> > kernel oops log in the following link:
> >
> >         https://lore.kernel.org/lkml/20200916202026.GC38283@xxxxxxx/
>
> The failure signature is similar to
> https://lore.kernel.org/lkml/20200901075321.GL4299@shao2-debian/
>
> >
> > And the kernel config is the one(without KASAN) used by Theodore in GCE VM, see
> > the following link:
> >
> >         https://lore.kernel.org/lkml/20200917143012.GF38283@xxxxxxx/
> >
> > The reproducer is xfstests generic/038. In my setting, test device is virtio-scsi, and
> > scratch device is virtio-blk.

Is it possible to check SLUB as well to confirm that the issue is only
happening on SLAB?