linux-kernel - Re: block/badblocks.c warning in 6.7-rc2

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Message-Id: <C8305655-3749-411B-A696-E07E95882215@suse.de>
Date:   Wed, 29 Nov 2023 16:08:25 +0800
From:   Coly Li <colyli@...e.de>
To:     Bagas Sanjaya <bagasdotme@...il.com>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux Regressions <regressions@...ts.linux.dev>,
        Linux Block Devices <linux-block@...r.kernel.org>,
        Linux RAID <linux-raid@...r.kernel.org>,
        Linux bcachefs <linux-bcachefs@...r.kernel.org>,
        Xiao Ni <xni@...hat.com>, Geliang Tang <geliang.tang@...e.com>,
        Jens Axboe <axboe@...nel.dk>, Song Liu <song@...nel.org>,
        Kent Overstreet <kent.overstreet@...ux.dev>,
        Janpieter Sollie <janpieter.sollie@...net.be>
Subject: Re: block/badblocks.c warning in 6.7-rc2



> 2023年11月29日 07:47，Bagas Sanjaya <bagasdotme@...il.com> 写道：
> 
> Hi,
> 
> I notice a regression report that is rather well-handled on Bugzilla [1].
> Quoting from it:
> 
>> 
>> 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) 
>> 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
> 
> The culprit author then replied:
> 
>> The warning is from this line of code in _badblocks_check(),
>> 1284         WARN_ON(bb->shift < 0 || sectors == 0);
>> 
>> It means the caller sent an invalid range to check. From the oops information,
>> "RDX: 0000000000000000" means parameter 'sectors' is 0.
>> 
>> 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().
> 
> See Bugzilla for the full thread and attached decoded dmesg and kernel config.
> 
> Anyway, I'm adding this regression to regzbot:
> 
> #regzbot introduced: 3ea3354cb9f03e https://bugzilla.kernel.org/show_bug.cgi?id=218184
> #regzbot title: badblocks_check regression (md error handling) on bcachefs volume
> 
> Thanks.
> 
> [1]: https://bugzilla.kernel.org/show_bug.cgi?id=218184

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