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| author | Qu Wenruo <wqu@suse.com> | 2021-12-16 19:47:35 +0800 |
|---|---|---|
| committer | David Sterba <dsterba@suse.com> | 2022-01-31 16:05:16 +0100 |
| commit | 2d192fc4c1abeb0d04d1c8cd54405ff4a0b0255b (patch) | |
| tree | c8a541365058a743db3d60558c7278646aa43c95 /fs | |
| parent | 27cdfde181bcacd226c230b2fd831f6f5b8c215f (diff) | |
btrfs: don't start transaction for scrub if the fs is mounted read-only
[BUG]
The following super simple script would crash btrfs at unmount time, if
CONFIG_BTRFS_ASSERT() is set.
mkfs.btrfs -f $dev
mount $dev $mnt
xfs_io -f -c "pwrite 0 4k" $mnt/file
umount $mnt
mount -r ro $dev $mnt
btrfs scrub start -Br $mnt
umount $mnt
This will trigger the following ASSERT() introduced by commit
0a31daa4b602 ("btrfs: add assertion for empty list of transactions at
late stage of umount").
That patch is definitely not the cause, it just makes enough noise for
developers.
[CAUSE]
We will start transaction for the following call chain during scrub:
scrub_enumerate_chunks()
|- btrfs_inc_block_group_ro()
|- btrfs_join_transaction()
However for RO mount, there is no running transaction at all, thus
btrfs_join_transaction() will start a new transaction.
Furthermore, since it's read-only mount, btrfs_sync_fs() will not call
btrfs_commit_super() to commit the new but empty transaction.
And leads to the ASSERT().
The bug has been there for a long time. Only the new ASSERT() makes it
noisy enough to be noticed.
[FIX]
For read-only scrub on read-only mount, there is no need to start a
transaction nor to allocate new chunks in btrfs_inc_block_group_ro().
Just do extra read-only mount check in btrfs_inc_block_group_ro(), and
if it's read-only, skip all chunk allocation and go inc_block_group_ro()
directly.
CC: stable@vger.kernel.org # 5.4+
Signed-off-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Diffstat (limited to 'fs')
| -rw-r--r-- | fs/btrfs/block-group.c | 13 |
1 files changed, 13 insertions, 0 deletions
diff --git a/fs/btrfs/block-group.c b/fs/btrfs/block-group.c index 1db24e6d6d90..68feabc83a27 100644 --- a/fs/btrfs/block-group.c +++ b/fs/btrfs/block-group.c @@ -2544,6 +2544,19 @@ int btrfs_inc_block_group_ro(struct btrfs_block_group *cache, int ret; bool dirty_bg_running; + /* + * This can only happen when we are doing read-only scrub on read-only + * mount. + * In that case we should not start a new transaction on read-only fs. + * Thus here we skip all chunk allocations. + */ + if (sb_rdonly(fs_info->sb)) { + mutex_lock(&fs_info->ro_block_group_mutex); + ret = inc_block_group_ro(cache, 0); + mutex_unlock(&fs_info->ro_block_group_mutex); + return ret; + } + do { trans = btrfs_join_transaction(root); if (IS_ERR(trans)) |