diff options
| author | Qu Wenruo | 2020-07-13 09:03:20 +0800 |
|---|---|---|
| committer | David Sterba | 2020-07-27 12:55:45 +0200 |
| commit | f3e3d9cc35252a70a2fd698762c9687718268ec6 (patch) | |
| tree | 7e6ef19521ca26695d3bd3f001650f61d8bdf2a3 /fs | |
| parent | 5cb502f4ab6469c3d02bd787a3ff58a7b624ba67 (diff) | |
btrfs: avoid possible signal interruption of btrfs_drop_snapshot() on relocation tree
[BUG]
There is a bug report about bad signal timing could lead to read-only
fs during balance:
BTRFS info (device xvdb): balance: start -d -m -s
BTRFS info (device xvdb): relocating block group 73001861120 flags metadata
BTRFS info (device xvdb): found 12236 extents, stage: move data extents
BTRFS info (device xvdb): relocating block group 71928119296 flags data
BTRFS info (device xvdb): found 3 extents, stage: move data extents
BTRFS info (device xvdb): found 3 extents, stage: update data pointers
BTRFS info (device xvdb): relocating block group 60922265600 flags metadata
BTRFS: error (device xvdb) in btrfs_drop_snapshot:5505: errno=-4 unknown
BTRFS info (device xvdb): forced readonly
BTRFS info (device xvdb): balance: ended with status: -4
[CAUSE]
The direct cause is the -EINTR from the following call chain when a
fatal signal is pending:
relocate_block_group()
|- clean_dirty_subvols()
|- btrfs_drop_snapshot()
|- btrfs_start_transaction()
|- btrfs_delayed_refs_rsv_refill()
|- btrfs_reserve_metadata_bytes()
|- __reserve_metadata_bytes()
|- wait_reserve_ticket()
|- prepare_to_wait_event();
|- ticket->error = -EINTR;
Normally this behavior is fine for most btrfs_start_transaction()
callers, as they need to catch any other error, same for the signal, and
exit ASAP.
However for balance, especially for the clean_dirty_subvols() case, we're
already doing cleanup works, getting -EINTR from btrfs_drop_snapshot()
could cause a lot of unexpected problems.
From the mentioned forced read-only report, to later balance error due
to half dropped reloc trees.
[FIX]
Fix this problem by using btrfs_join_transaction() if
btrfs_drop_snapshot() is called from relocation context.
Since btrfs_join_transaction() won't get interrupted by signal, we can
continue the cleanup.
CC: stable@vger.kernel.org # 5.4+
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>3
Signed-off-by: David Sterba <dsterba@suse.com>
Diffstat (limited to 'fs')
| -rw-r--r-- | fs/btrfs/extent-tree.c | 9 |
1 files changed, 8 insertions, 1 deletions
diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c index 96223813b618..61ede335f6c3 100644 --- a/fs/btrfs/extent-tree.c +++ b/fs/btrfs/extent-tree.c @@ -5298,7 +5298,14 @@ int btrfs_drop_snapshot(struct btrfs_root *root, int update_ref, int for_reloc) goto out; } - trans = btrfs_start_transaction(tree_root, 0); + /* + * Use join to avoid potential EINTR from transaction start. See + * wait_reserve_ticket and the whole reservation callchain. + */ + if (for_reloc) + trans = btrfs_join_transaction(tree_root); + else + trans = btrfs_start_transaction(tree_root, 0); if (IS_ERR(trans)) { err = PTR_ERR(trans); goto out_free; |