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List:       linux-xfs
Subject:    Re: [PATCH] xfs: don't allow log writes if the data device is readonly
From:       "Darrick J. Wong" <djwong () kernel ! org>
Date:       2021-04-30 15:14:24
Message-ID: 20210430151424.GP3122264 () magnolia
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On Fri, Apr 30, 2021 at 09:32:48AM -0400, Brian Foster wrote:
> On Thu, Apr 29, 2021 at 05:40:12PM -0700, Darrick J. Wong wrote:
> > From: Darrick J. Wong <djwong@kernel.org>
> > 
> > While running generic/050 with an external log, I observed this warning
> > in dmesg:
> > 
> > Trying to write to read-only block-device sda4 (partno 4)
> > WARNING: CPU: 2 PID: 215677 at block/blk-core.c:704 submit_bio_checks+0x256/0x510
> > Call Trace:
> >  submit_bio_noacct+0x2c/0x430
> >  _xfs_buf_ioapply+0x283/0x3c0 [xfs]
> >  __xfs_buf_submit+0x6a/0x210 [xfs]
> >  xfs_buf_delwri_submit_buffers+0xf8/0x270 [xfs]
> >  xfsaild+0x2db/0xc50 [xfs]
> >  kthread+0x14b/0x170
> > 
> > I think this happened because we tried to cover the log after a readonly
> > mount, and the AIL tried to write the primary superblock to the data
> > device.  The test marks the data device readonly, but it doesn't do the
> > same to the external log device.  Therefore, XFS thinks that the log is
> > writable, even though AIL writes whine to dmesg because the data device
> > is read only.
> > 
> > Fix this by amending xfs_log_writable to prevent writes when the AIL
> > can't possible write anything into the filesystem.
> > 
> > Note: As for the external log or the rt devices being readonly--
> > xfs_blkdev_get will complain about that if we aren't doing a norecovery
> > mount.
> > 
> > Signed-off-by: Darrick J. Wong <djwong@kernel.org>
> > ---
> >  fs/xfs/xfs_log.c |    4 +++-
> >  1 file changed, 3 insertions(+), 1 deletion(-)
> > 
> > diff --git a/fs/xfs/xfs_log.c b/fs/xfs/xfs_log.c
> > index 06041834daa3..e4839f22ec07 100644
> > --- a/fs/xfs/xfs_log.c
> > +++ b/fs/xfs/xfs_log.c
> > @@ -358,12 +358,14 @@ xfs_log_writable(
> >  	 * Never write to the log on norecovery mounts, if the block device is
> >  	 * read-only, or if the filesystem is shutdown. Read-only mounts still
> >  	 * allow internal writes for log recovery and unmount purposes, so don't
> > -	 * restrict that case here.
> > +	 * restrict that case here unless the data device is also readonly.
> >  	 */
> 
> The comment update is a little confusing because that second sentence
> explicitly refers to the read-only mount case (i.e., why we don't check
> XFS_MOUNT_RDONLY here), and that logic/reasoning remains independent of
> this change. Perhaps instead change the first part to something like
> "... if the data or log device is read-only, ..." ?

Will do.  Thanks for the review!

--D

> With that fixed up:
> 
> Reviewed-by: Brian Foster <bfoster@redhat.com>
> 
> >  	if (mp->m_flags & XFS_MOUNT_NORECOVERY)
> >  		return false;
> >  	if (xfs_readonly_buftarg(mp->m_log->l_targ))
> >  		return false;
> > +	if (xfs_readonly_buftarg(mp->m_ddev_targp))
> > +		return false;
> >  	if (XFS_FORCED_SHUTDOWN(mp))
> >  		return false;
> >  	return true;
> > 
> 
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