On Wed, Dec 15, 2021 at 07:58:58PM -0800, Darrick J. Wong wrote:
> On Wed, Dec 15, 2021 at 05:10:54PM -0800, Darrick J. Wong wrote:
> > On Thu, Dec 16, 2021 at 11:17:09AM +1100, Dave Chinner wrote:
> > > From: Dave Chinner <dchinner@xxxxxxxxxx>
> > >
> > > Got a report that a repeated crash test of a container host would
> > > eventually fail with a log recovery error preventing the system from
> > > mounting the root filesystem. It manifested as a directory leaf node
> > > corruption on writeback like so:
> > >
> > > XFS (loop0): Mounting V5 Filesystem
> > > XFS (loop0): Starting recovery (logdev: internal)
> > > XFS (loop0): Metadata corruption detected at xfs_dir3_leaf_check_int+0x99/0xf0, xfs_dir3_leaf1 block 0x12faa158
> > > XFS (loop0): Unmount and run xfs_repair
> > > XFS (loop0): First 128 bytes of corrupted metadata buffer:
> > > 00000000: 00 00 00 00 00 00 00 00 3d f1 00 00 e1 9e d5 8b ........=.......
> > > 00000010: 00 00 00 00 12 fa a1 58 00 00 00 29 00 00 1b cc .......X...)....
> > > 00000020: 91 06 78 ff f7 7e 4a 7d 8d 53 86 f2 ac 47 a8 23 ..x..~J}.S...G.#
> > > 00000030: 00 00 00 00 17 e0 00 80 00 43 00 00 00 00 00 00 .........C......
> > > 00000040: 00 00 00 2e 00 00 00 08 00 00 17 2e 00 00 00 0a ................
> > > 00000050: 02 35 79 83 00 00 00 30 04 d3 b4 80 00 00 01 50 .5y....0.......P
> > > 00000060: 08 40 95 7f 00 00 02 98 08 41 fe b7 00 00 02 d4 .@.......A......
> > > 00000070: 0d 62 ef a7 00 00 01 f2 14 50 21 41 00 00 00 0c .b.......P!A....
> > > XFS (loop0): Corruption of in-memory data (0x8) detected at xfs_do_force_shutdown+0x1a/0x20 (fs/xfs/xfs_buf.c:1514). Shutting down.
> > > XFS (loop0): Please unmount the filesystem and rectify the problem(s)
> > > XFS (loop0): log mount/recovery failed: error -117
> > > XFS (loop0): log mount failed
> > >
> > > Tracing indicated that we were recovering changes from a transaction
> > > at LSN 0x29/0x1c16 into a buffer that had an LSN of 0x29/0x1d57.
> > > That is, log recovery was overwriting a buffer with newer changes on
> > > disk than was in the transaction. Tracing indicated that we were
> > > hitting the "recovery immediately" case in
> > > xfs_buf_log_recovery_lsn(), and hence it was ignoring the LSN in the
> > > buffer.
> > >
> > > The code was extracting the LSN correctly, then ignoring it because
> > > the UUID in the buffer did not match the superblock UUID. The
> > > problem arises because the UUID check uses the wrong UUID - it
> > > should be checking the sb_meta_uuid, not sb_uuid. This filesystem
> > > has sb_uuid != sb_meta_uuid (which is fine), and the buffer has the
> > > correct matching sb_meta_uuid in it, it's just the code checked it
> > > against the wrong superblock uuid.
> > >
> > > The is no corruption in the filesystem, and failing to recover the
> > > buffer due to a write verifier failure means the recovery bug did
> > > not propagate the corruption to disk. Hence there is no corruption
> > > before or after this bug has manifested, the impact is limited
> > > simply to an unmountable filesystem....
> > >
> > > This was missed back in 2015 during an audit of incorrect sb_uuid
> > > usage that resulted in commit fcfbe2c4ef42 ("xfs: log recovery needs
> > > to validate against sb_meta_uuid") that fixed the magic32 buffers to
> > > validate against sb_meta_uuid instead of sb_uuid. It missed the
> > > magicda buffers....
> > >
> > > Fixes: ce748eaa65f2 ("xfs: create new metadata UUID field and incompat flag")
> > > Signed-off-by: Dave Chinner <dchinner@xxxxxxxxxx>
> >
> > Makes sense. Please send a slimmed down version of this to fstests@.
>
> <sigh> "...of a reproducer for this to fstests@."
I don't have one. All I have a pre-recovery metadump that has the
issue already in it, and I traced the mount and looked at log print
output to find the issue.
Eric, it seems like getting generic coverage of sb_meta_uuid !=
sb_uuid for at least the recoveryloop group tests would be a goof
thing for the QE team to add to fstests? Alternatively, randomly
decide whether to set a different UUID during each scratch_mkfs
call?
Cheers,
Dave.
--
Dave Chinner
david@xxxxxxxxxxxxx
