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| author | Josef Bacik <josef@toxicpanda.com> | 2022-09-30 16:45:08 -0400 |
|---|---|---|
| committer | David Sterba <dsterba@suse.com> | 2022-10-11 14:47:06 +0200 |
| commit | 9e769bd7e5db5e3bd76e7c67004c261f7fcaa8f1 (patch) | |
| tree | 3c079df3099eb2edb18a15e1ca9f4e92585af921 /fs/btrfs | |
| parent | c86eab81a23f368d08efd3df96a95f3d0b471f85 (diff) | |
| download | linux-9e769bd7e5db5e3bd76e7c67004c261f7fcaa8f1.tar.bz2 | |
btrfs: unlock locked extent area if we have contention
In production we hit the following deadlock
task 1 task 2 task 3
------ ------ ------
fiemap(file) falloc(file) fsync(file)
write(0, 1MiB)
btrfs_commit_transaction()
wait_on(!pending_ordered)
lock(512MiB, 1GiB)
start_transaction
wait_on_transaction
lock(0, 1GiB)
wait_extent_bit(512MiB)
task 4
------
finish_ordered_extent(0, 1MiB)
lock(0, 1MiB)
**DEADLOCK**
This occurs because when task 1 does it's lock, it locks everything from
0-512MiB, and then waits for the 512MiB chunk to unlock. task 2 will
never unlock because it's waiting on the transaction commit to happen,
the transaction commit is waiting for the outstanding ordered extents,
and then the ordered extent thread is blocked waiting on the 0-1MiB
range to unlock.
To fix this we have to clear anything we've locked so far, wait for the
extent_state that we contended on, and then try to re-lock the entire
range again.
CC: stable@vger.kernel.org # 5.15+
Reviewed-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Diffstat (limited to 'fs/btrfs')
| -rw-r--r-- | fs/btrfs/extent-io-tree.c | 15 |
1 files changed, 8 insertions, 7 deletions
diff --git a/fs/btrfs/extent-io-tree.c b/fs/btrfs/extent-io-tree.c index 618275af19c4..83cb0378096f 100644 --- a/fs/btrfs/extent-io-tree.c +++ b/fs/btrfs/extent-io-tree.c @@ -1641,16 +1641,17 @@ int lock_extent(struct extent_io_tree *tree, u64 start, u64 end, int err; u64 failed_start; - while (1) { + err = __set_extent_bit(tree, start, end, EXTENT_LOCKED, &failed_start, + cached_state, NULL, GFP_NOFS); + while (err == -EEXIST) { + if (failed_start != start) + clear_extent_bit(tree, start, failed_start - 1, + EXTENT_LOCKED, cached_state); + + wait_extent_bit(tree, failed_start, end, EXTENT_LOCKED); err = __set_extent_bit(tree, start, end, EXTENT_LOCKED, &failed_start, cached_state, NULL, GFP_NOFS); - if (err == -EEXIST) { - wait_extent_bit(tree, failed_start, end, EXTENT_LOCKED); - start = failed_start; - } else - break; - WARN_ON(start > end); } return err; } |