linux-ext4 - Re: [BUG] invalid superblock checksum possibly due to race

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Message-ID: <CAABuPhZrQXQ8-tFu9V3575by5N3RV7jd-OcOjy_pLw_na1OUkw@mail.gmail.com>
Date:   Tue, 30 Jun 2020 11:34:49 -0700
From:   Costa Sapuntzakis <costa@...estorage.com>
To:     Jan Kara <jack@...e.cz>
Cc:     linux-ext4@...r.kernel.org
Subject: Re: [BUG] invalid superblock checksum possibly due to race

Hello and thank you!

> Yes, probably ext4_superblock_csum_set() should use
>
> lock_buffer(EXT4_SB(sb)->s_sbh)
>
> to synchronize updating of superblock checksum. Will you send a patch?

Yes. I will send a patch.

I noticed lock_buffer can sleep. That would seem to imply to me that
lock_buffer can be held across I/Os.
I worry that this will occasionally significantly slow down this code
path compared to what it used to be.  Are there any things
about the way ext4 uses buffers that makes this less of a concern?

-Costa