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Date:   Wed, 1 Jul 2020 18:22:48 +0200
From:   Jan Kara <>
To:     Costa Sapuntzakis <>
Cc:     Jan Kara <>,
Subject: Re: [BUG] invalid superblock checksum possibly due to race


On Tue 30-06-20 11:34:49, Costa Sapuntzakis wrote:
> > 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?

Yes, buffer lock is a sleeping lock but that's the lock we usually use to
protect consistency of buffer contents. So I prefer to use that lock unless
we have definitive performance data showing we need something more

Jan Kara <>

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