linux-ext4 - Re: [PATCH] writeback: avoid double-writing the inode on a lazytime expiration

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Message-ID: <20200311125749.GA7159@mit.edu>
Date:   Wed, 11 Mar 2020 08:57:49 -0400
From:   "Theodore Y. Ts'o" <tytso@....edu>
To:     Eric Biggers <ebiggers@...nel.org>
Cc:     Linux Filesystem Development List <linux-fsdevel@...r.kernel.org>,
        Ext4 Developers List <linux-ext4@...r.kernel.org>,
        linux-f2fs-devel@...ts.sourceforge.net
Subject: Re: [PATCH] writeback: avoid double-writing the inode on a lazytime
 expiration

On Tue, Mar 10, 2020 at 08:20:09PM -0700, Eric Biggers wrote:
> Thanks Ted!  This fixes the fscrypt test failure.
> 
> However, are you sure this works correctly on all filesystems?  I'm not sure
> about XFS.  XFS only implements ->dirty_inode(), not ->write_inode(), and in its
> ->dirty_inode() it does:
  ...
> 		if (flag != I_DIRTY_SYNC || !(inode->i_state & I_DIRTY_TIME))
> 			return;

That's true, but when the timestamps were originally modified,
dirty_inode() will be called with flag == I_DIRTY_TIME, which will
*not* be a no-op; which is to say, XFS will force the timestamps to be
updated on disk when the timestamps are first dirtied, because it
doesn't support I_DIRTY_TIME.

So I think we're fine.

					- Ted