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Date:   Fri, 2 Apr 2021 10:37:04 +0530
From:   Ritesh Harjani <ritesh.list@gmail.com>
To:     Eric Whitney <enwlinux@gmail.com>
Cc:     linux-ext4@vger.kernel.org, tytso@mit.edu, willy@infradead.org,
        Ritesh Harjani <ritesh.list@gmail.com>
Subject: Re: generic/418 regression seen on 5.12-rc3
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On 21/03/18 02:16PM, Eric Whitney wrote:
> As mentioned in today's ext4 concall, I've seen generic/418 fail from time to
> time when run on 5.12-rc3 and 5.12-rc1 kernels.  This first occurred when
> running the 1k test case using kvm-xfstests.  I was then able to bisect the
> failure to a patch landed in the -rc1 merge window:
>
> (bd8a1f3655a7) mm/filemap: support readpage splitting a page
>
> Typical test output resulting from a failure looks like:
>
>      QA output created by 418
>     +cmpbuf: offset 0: Expected: 0x1, got 0x0
>     +[6:0] FAIL - comparison failed, offset 3072
>     +diotest -w -b 512 -n 8 -i 4 failed at loop 0
>      Silence is golden
>     ...
>
> I've also been able to reproduce the failure on -rc3 in the 4k test case as
> well.  The failure frequency there was 10 out of 100 runs.  It was anywhere
> from 2 to 8 failures out of 100 runs in the 1k case.

Ok, I kept the test running for overnight on PPC64, since as you mentioned
the reproducibility rate is less.

./check -I 1000 tests/generic/418  // this stops the test as soon as we hit it.

I could hit the test on 8th iteration of the test.
Note this is 4k blocksize on 64K pagesize.

<logs>
======
SECTION       -- ext4_4k
FSTYP         -- ext4
PLATFORM      -- Linux/ppc64le qemu 5.12.0-rc2-00313-gae9fda3a723 #66 SMP Sun Mar 14 23:05:24 CDT 2021
MKFS_OPTIONS  -- -F -b4096 -I 256 -O 64bit /dev/loop3
MOUNT_OPTIONS -- -o block_validity /dev/loop3 /mnt1/scratch

generic/418 320s ... - output mismatch (see /home/qemu/work-tools/xfstests/results//ext4_4k/generic/418.out.bad)
    --- tests/generic/418.out   2020-08-04 09:59:08.658307281 +0000
    +++ /home/qemu/work-tools/xfstests/results//ext4_4k/generic/418.out.bad     2021-04-01 18:27:47.498465793 +0000
    @@ -1,2 +1,5 @@
     QA output created by 418
    +cmpbuf: offset 0: Expected: 0x1, got 0x0
    +[1:0] FAIL - comparison failed, offset 32768
    +diotest -w -b 32768 -n 3 -i 1 failed at loop 6
     Silence is golden
Ran: generic/418
Failures: generic/418
Failed 1 of 1 tests

-ritesh