From: Josef Bacik josef@toxicpanda.com
commit bf7ba8ee759b7b7a34787ddd8dc3f190a3d7fa24 upstream.
We are hitting the following deadlock in production occasionally
Task 1 Task 2 Task 3 Task 4 Task 5 fsync(A) start trans start commit falloc(A) lock 5m-10m start trans wait for commit fiemap(A) lock 0-10m wait for 5m-10m (have 0-5m locked)
have btrfs_need_log_full_commit !full_sync wait_ordered_extents finish_ordered_io(A) lock 0-5m DEADLOCK
We have an existing dependency of file extent lock -> transaction. However in fsync if we tried to do the fast logging, but then had to fall back to committing the transaction, we will be forced to call btrfs_wait_ordered_range() to make sure all of our extents are updated.
This creates a dependency of transaction -> file extent lock, because btrfs_finish_ordered_io() will need to take the file extent lock in order to run the ordered extents.
Fix this by stopping the transaction if we have to do the full commit and we attempted to do the fast logging. Then attach to the transaction and commit it if we need to.
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 Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- fs/btrfs/file.c | 67 +++++++++++++++++++++++++++++++++++++++++++------------- 1 file changed, 52 insertions(+), 15 deletions(-)
--- a/fs/btrfs/file.c +++ b/fs/btrfs/file.c @@ -2359,25 +2359,62 @@ int btrfs_sync_file(struct file *file, l */ btrfs_inode_unlock(inode, BTRFS_ILOCK_MMAP);
- if (ret != BTRFS_NO_LOG_SYNC) { + if (ret == BTRFS_NO_LOG_SYNC) { + ret = btrfs_end_transaction(trans); + goto out; + } + + /* We successfully logged the inode, attempt to sync the log. */ + if (!ret) { + ret = btrfs_sync_log(trans, root, &ctx); if (!ret) { - ret = btrfs_sync_log(trans, root, &ctx); - if (!ret) { - ret = btrfs_end_transaction(trans); - goto out; - } + ret = btrfs_end_transaction(trans); + goto out; } - if (!full_sync) { - ret = btrfs_wait_ordered_range(inode, start, len); - if (ret) { - btrfs_end_transaction(trans); - goto out; - } - } - ret = btrfs_commit_transaction(trans); - } else { + } + + /* + * At this point we need to commit the transaction because we had + * btrfs_need_log_full_commit() or some other error. + * + * If we didn't do a full sync we have to stop the trans handle, wait on + * the ordered extents, start it again and commit the transaction. If + * we attempt to wait on the ordered extents here we could deadlock with + * something like fallocate() that is holding the extent lock trying to + * start a transaction while some other thread is trying to commit the + * transaction while we (fsync) are currently holding the transaction + * open. + */ + if (!full_sync) { ret = btrfs_end_transaction(trans); + if (ret) + goto out; + ret = btrfs_wait_ordered_range(inode, start, len); + if (ret) + goto out; + + /* + * This is safe to use here because we're only interested in + * making sure the transaction that had the ordered extents is + * committed. We aren't waiting on anything past this point, + * we're purely getting the transaction and committing it. + */ + trans = btrfs_attach_transaction_barrier(root); + if (IS_ERR(trans)) { + ret = PTR_ERR(trans); + + /* + * We committed the transaction and there's no currently + * running transaction, this means everything we care + * about made it to disk and we are done. + */ + if (ret == -ENOENT) + ret = 0; + goto out; + } } + + ret = btrfs_commit_transaction(trans); out: ASSERT(list_empty(&ctx.list)); err = file_check_and_advance_wb_err(file);