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

[Ming Lei <ming.lei@redhat.com>]

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@mit.edu/

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@mit.edu/

The reproducer is xfstests generic/038. In my setting, test device is virtio-scsi, and
scratch device is virtio-blk.


[1] git bisect log:

git bisect start
# good: [568f2700657794b8258e72983ba508793a658942] blk-mq: centralise related handling into blk_mq_get_driver_tag
git bisect good 568f2700657794b8258e72983ba508793a658942
# bad: [f4d51dffc6c01a9e94650d95ce0104964f8ae822] Linux 5.9-rc4
git bisect bad f4d51dffc6c01a9e94650d95ce0104964f8ae822
# good: [8186749621ed6b8fc42644c399e8c755a2b6f630] Merge tag 'drm-next-2020-08-06' of git://anongit.freedesktop.org/drm/drm
git bisect good 8186749621ed6b8fc42644c399e8c755a2b6f630
# good: [60e76bb8a4e4c5398ea9053535e1fd0c9d6bb06e] Merge tag 'm68knommu-for-v5.9' of git://git.kernel.org/pub/scm/linux/kernel/git/gerg/m68knommu
git bisect good 60e76bb8a4e4c5398ea9053535e1fd0c9d6bb06e
# bad: [57b077939287835b9396a1c3b40d35609cf2fcb8] Merge tag 'for_linus' of git://git.kernel.org/pub/scm/linux/kernel/git/mst/vhost
git bisect bad 57b077939287835b9396a1c3b40d35609cf2fcb8
# bad: [0f43283be7fec4a76cd4ed50dc37db30719bde05] Merge branch 'work.fdpic' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs
git bisect bad 0f43283be7fec4a76cd4ed50dc37db30719bde05
# good: [5631c5e0eb9035d92ceb20fcd9cdb7779a3f5cc7] Merge tag 'xfs-5.9-merge-7' of git://git.kernel.org/pub/scm/fs/xfs/xfs-linux
git bisect good 5631c5e0eb9035d92ceb20fcd9cdb7779a3f5cc7
# good: [e3083c3f369700cd1eec3de93b8d8ec0918ff778] media: cafe-driver: use generic power management
git bisect good e3083c3f369700cd1eec3de93b8d8ec0918ff778
# bad: [42742d9bde2a8e11ec932cb5821f720a40a7c2a9] mm: thp: replace HTTP links with HTTPS ones
git bisect bad 42742d9bde2a8e11ec932cb5821f720a40a7c2a9
# bad: [10befea91b61c4e2c2d1df06a2e978d182fcf792] mm: memcg/slab: use a single set of kmem_caches for all allocations
git bisect bad 10befea91b61c4e2c2d1df06a2e978d182fcf792
# good: [cfbe1636c3585c1e032bfac512fb8be903fbc913] mm, kcsan: instrument SLAB/SLUB free with "ASSERT_EXCLUSIVE_ACCESS"
git bisect good cfbe1636c3585c1e032bfac512fb8be903fbc913
# good: [0f190a7ab78878f9e6c6930fc0f5f92c1250b57d] mm/page_io.c: use blk_io_schedule() for avoiding task hung in sync io
git bisect good 0f190a7ab78878f9e6c6930fc0f5f92c1250b57d
# good: [286e04b8ed7a04279ae277f0f024430246ea5eec] mm: memcg/slab: allocate obj_cgroups for non-root slab pages
git bisect good 286e04b8ed7a04279ae277f0f024430246ea5eec
# good: [9855609bde03e2472b99a95e869d29ee1e78a751] mm: memcg/slab: use a single set of kmem_caches for all accounted allocations
git bisect good 9855609bde03e2472b99a95e869d29ee1e78a751
# good: [272911a4ad18c48f8bc449a5db945a54987dd687] mm: memcg/slab: remove memcg_kmem_get_cache()
git bisect good 272911a4ad18c48f8bc449a5db945a54987dd687
# good: [15999eef7f25e2ea6a1c33f026166f472c5714e9] mm: memcg/slab: remove redundant check in memcg_accumulate_slabinfo()
git bisect good 15999eef7f25e2ea6a1c33f026166f472c5714e9
# first bad commit: [10befea91b61c4e2c2d1df06a2e978d182fcf792] mm: memcg/slab: use a single set of kmem_caches for all allocations



Thanks,
Ming