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| author | Darrick J. Wong <djwong@kernel.org> | 2022-04-11 23:49:42 +0300 |
|---|---|---|
| committer | Dave Chinner <david@fromorbit.com> | 2022-04-11 23:49:42 +0300 |
| commit | 5a605fd6cb1da0ec9cb6e54c06bcf58f706d2f83 (patch) | |
| tree | 6c8eb64e5290bb466b46aab89c6917c40e6c5245 /fs/xfs/xfs_rtalloc.h | |
| parent | f34061f554feba68e12b7a73008c350d2a9afd0c (diff) | |
| download | linux-5a605fd6cb1da0ec9cb6e54c06bcf58f706d2f83.tar.xz | |
xfs: recalculate free rt extents after log recovery
I've been observing periodic corruption reports from xfs_scrub involving
the free rt extent counter (frextents) while running xfs/141. That test
uses an error injection knob to induce a torn write to the log, and an
arbitrary number of recovery mounts, frextents will count fewer free rt
extents than can be found the rtbitmap.
The root cause of the problem is a combination of the misuse of
sb_frextents in the incore mount to reflect both incore reservations
made by running transactions as well as the actual count of free rt
extents on disk. The following sequence can reproduce the undercount:
Thread 1 Thread 2
xfs_trans_alloc(rtextents=3)
xfs_mod_frextents(-3)
<blocks>
xfs_attr_set()
xfs_bmap_attr_addfork()
xfs_add_attr2()
xfs_log_sb()
xfs_sb_to_disk()
xfs_trans_commit()
<log flushed to disk>
<log goes down>
Note that thread 1 subtracts 3 from sb_frextents even though it never
commits to using that space. Thread 2 writes the undercounted value to
the ondisk superblock and logs it to the xattr transaction, which is
then flushed to disk. At next mount, log recovery will find the logged
superblock and write that back into the filesystem. At the end of log
recovery, we reread the superblock and install the recovered
undercounted frextents value into the incore superblock. From that
point on, we've effectively leaked thread 1's transaction reservation.
The correct fix for this is to separate the incore reservation from the
ondisk usage, but that's a matter for the next patch. Because the
kernel has been logging superblocks with undercounted frextents for a
very long time and we don't demand that sysadmins run xfs_repair after a
crash, fix the undercount by recomputing frextents after log recovery.
Gating this on log recovery is a reasonable balance (I think) between
correcting the problem and slowing down every mount attempt. Note that
xfs_repair will fix undercounted frextents.
Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>
Diffstat (limited to 'fs/xfs/xfs_rtalloc.h')
| -rw-r--r-- | fs/xfs/xfs_rtalloc.h | 2 |
1 files changed, 2 insertions, 0 deletions
diff --git a/fs/xfs/xfs_rtalloc.h b/fs/xfs/xfs_rtalloc.h index 539d134f4f25..62c7ad79cbb6 100644 --- a/fs/xfs/xfs_rtalloc.h +++ b/fs/xfs/xfs_rtalloc.h @@ -135,6 +135,7 @@ bool xfs_verify_rtbno(struct xfs_mount *mp, xfs_rtblock_t rtbno); int xfs_rtalloc_extent_is_free(struct xfs_mount *mp, struct xfs_trans *tp, xfs_rtblock_t start, xfs_extlen_t len, bool *is_free); +int xfs_rtalloc_reinit_frextents(struct xfs_mount *mp); #else # define xfs_rtallocate_extent(t,b,min,max,l,f,p,rb) (ENOSYS) # define xfs_rtfree_extent(t,b,l) (ENOSYS) @@ -145,6 +146,7 @@ int xfs_rtalloc_extent_is_free(struct xfs_mount *mp, struct xfs_trans *tp, # define xfs_rtbuf_get(m,t,b,i,p) (ENOSYS) # define xfs_verify_rtbno(m, r) (false) # define xfs_rtalloc_extent_is_free(m,t,s,l,i) (ENOSYS) +# define xfs_rtalloc_reinit_frextents(m) (0) static inline int /* error */ xfs_rtmount_init( xfs_mount_t *mp) /* file system mount structure */ |