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Subject: Re: block/badblocks.c warning in 6.7-rc2
From:   Coly Li <colyli@suse.de>
In-Reply-To: <562a2442-d098-4972-baa1-5a843e06b180@gmail.com>
Date:   Wed, 29 Nov 2023 16:08:25 +0800
Cc:     Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Linux Regressions <regressions@lists.linux.dev>,
        Linux Block Devices <linux-block@vger.kernel.org>,
        Linux RAID <linux-raid@vger.kernel.org>,
        Linux bcachefs <linux-bcachefs@vger.kernel.org>,
        Xiao Ni <xni@redhat.com>, Geliang Tang <geliang.tang@suse.com>,
        Jens Axboe <axboe@kernel.dk>, Song Liu <song@kernel.org>,
        Kent Overstreet <kent.overstreet@linux.dev>,
        Janpieter Sollie <janpieter.sollie@edpnet.be>
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Message-Id: <C8305655-3749-411B-A696-E07E95882215@suse.de>
References: <562a2442-d098-4972-baa1-5a843e06b180@gmail.com>
To:     Bagas Sanjaya <bagasdotme@gmail.com>
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> 2023=E5=B9=B411=E6=9C=8829=E6=97=A5 07:47=EF=BC=8CBagas Sanjaya =
<bagasdotme@gmail.com> =E5=86=99=E9=81=93=EF=BC=9A
>=20
> Hi,
>=20
> I notice a regression report that is rather well-handled on Bugzilla =
[1].
> Quoting from it:
>=20
>>=20
>> when booting from 6.7-rc2, compiled with clang, I get this warning on =
one of my 3 bcachefs volumes:
>> WARNING: CPU: 3 PID: 712 at block/badblocks.c:1284 badblocks_check =
(block/badblocks.c:1284)=20
>> The reason why isn't clear, but the stack trace points to an error in =
md error handling.
>> This bug didn't happen in 6.6
>> there are 3 commits in 6.7-rc2 which may cause them,
>> in attachment:
>> - decoded stacktrace of dmesg
>> - kernel .config
>=20
> The culprit author then replied:
>=20
>> The warning is from this line of code in _badblocks_check(),
>> 1284         WARN_ON(bb->shift < 0 || sectors =3D=3D 0);
>>=20
>> It means the caller sent an invalid range to check. =46rom the oops =
information,
>> "RDX: 0000000000000000" means parameter 'sectors' is 0.
>>=20
>> So the question is, why does md raid code send a 0-length range for =
badblocks check? Is this behavior on purpose, or improper?
>> ...
>> IMHO, it doesn't make sense for caller to check a zero-length LBA =
range. The warning works as expect to detect improper call to =
badblocks_check().
>=20
> See Bugzilla for the full thread and attached decoded dmesg and kernel =
config.
>=20
> Anyway, I'm adding this regression to regzbot:
>=20
> #regzbot introduced: 3ea3354cb9f03e =
https://bugzilla.kernel.org/show_bug.cgi?id=3D218184
> #regzbot title: badblocks_check regression (md error handling) on =
bcachefs volume
>=20
> Thanks.
>=20
> [1]: https://bugzilla.kernel.org/show_bug.cgi?id=3D218184

It seems the improved bad blocks code caught a zero-size bio request =
from upper layer, this improper behavior was silently neglected before. =
It might be too early or simple to decide this is a regression, =
especially Janpieter closes the report for now.

Thanks.

Coly Li