linux-ext4 - Re: [PATCH 01/13] fs: avoid double-writing inodes on lazytime expiration

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Date:   Fri, 8 Jan 2021 09:54:32 +0100
From:   Christoph Hellwig <hch@....de>
To:     Eric Biggers <ebiggers@...nel.org>
Cc:     Jan Kara <jack@...e.cz>, linux-fsdevel@...r.kernel.org,
        linux-ext4@...r.kernel.org, linux-f2fs-devel@...ts.sourceforge.net,
        linux-xfs@...r.kernel.org, Theodore Ts'o <tytso@....edu>,
        Christoph Hellwig <hch@....de>, stable@...r.kernel.org
Subject: Re: [PATCH 01/13] fs: avoid double-writing inodes on lazytime
 expiration

On Thu, Jan 07, 2021 at 01:46:37PM -0800, Eric Biggers wrote:
> It looks like that's going to work, and it fixes the XFS bug too.
> 
> Note that if __writeback_single_inode() is called from writeback_single_inode()
> (rather than writeback_sb_inodes()), then the inode might not be queued for
> sync, in which case mark_inode_dirty_sync() will move it to a writeback list.
> 
> That's okay because afterwards, writeback_single_inode() will delete the inode
> from any writeback list if it's been fully cleaned, right?  So clean inodes
> won't get left on a writeback list.
> 
> It's confusing because there are comments in writeback_single_inode() and above
> __writeback_single_inode() that say that the inode must not be moved between
> writeback lists.  I take it that those comments are outdated, as they predate
> I_SYNC_QUEUED being introduced by commit 5afced3bf281 ("writeback: Avoid
> skipping inode writeback")?

Yes.  I think we need to update the comment as well.