btrfs: add lockdep annotations for the ordered extents wait event

This wait event is very similar to the pending ordered wait event in the
sense that it occurs in a different context than the condition signaling
for the event. The signaling occurs in btrfs_remove_ordered_extent()
while the wait event is implemented in btrfs_start_ordered_extent() in
fs/btrfs/ordered-data.c

However, in this case a thread must not acquire the lockdep map for the
ordered extents wait event when the ordered extent is related to a free
space inode. That is because lockdep creates dependencies between locks
acquired both in execution paths related to normal inodes and paths
related to free space inodes, thus leading to false positives.
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Ioannis Angelakopoulos <iangelak@fb.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/ctree.h

@@ -1100,6 +1100,7 @@ struct btrfs_fs_info {
 	struct lockdep_map btrfs_trans_num_extwriters_map;
 	struct lockdep_map btrfs_state_change_map[4];
 	struct lockdep_map btrfs_trans_pending_ordered_map;
+	struct lockdep_map btrfs_ordered_extent_map;
 
 #ifdef CONFIG_BTRFS_FS_REF_VERIFY
 	spinlock_t ref_verify_lock;

fs/btrfs/disk-io.c

@@ -2993,6 +2993,7 @@ void btrfs_init_fs_info(struct btrfs_fs_info *fs_info)
 	btrfs_lockdep_init_map(fs_info, btrfs_trans_num_writers);
 	btrfs_lockdep_init_map(fs_info, btrfs_trans_num_extwriters);
 	btrfs_lockdep_init_map(fs_info, btrfs_trans_pending_ordered);
+	btrfs_lockdep_init_map(fs_info, btrfs_ordered_extent);
 	btrfs_state_lockdep_init_map(fs_info, btrfs_trans_commit_start,
 				     BTRFS_LOCKDEP_TRANS_COMMIT_START);
 	btrfs_state_lockdep_init_map(fs_info, btrfs_trans_unblocked,

fs/btrfs/inode.c

@@ -3225,6 +3225,8 @@ int btrfs_finish_ordered_io(struct btrfs_ordered_extent *ordered_extent)
 		clear_bits |= EXTENT_DELALLOC_NEW;
 
 	freespace_inode = btrfs_is_free_space_inode(inode);
+	if (!freespace_inode)
+		btrfs_lockdep_acquire(fs_info, btrfs_ordered_extent);
 
 	if (test_bit(BTRFS_ORDERED_IOERR, &ordered_extent->flags)) {
 		ret = -EIO;
@@ -8959,6 +8961,7 @@ void btrfs_destroy_inode(struct inode *vfs_inode)
 	struct btrfs_ordered_extent *ordered;
 	struct btrfs_inode *inode = BTRFS_I(vfs_inode);
 	struct btrfs_root *root = inode->root;
+	bool freespace_inode;
 
 	WARN_ON(!hlist_empty(&vfs_inode->i_dentry));
 	WARN_ON(vfs_inode->i_data.nrpages);
@@ -8980,6 +8983,12 @@ void btrfs_destroy_inode(struct inode *vfs_inode)
 	if (!root)
 		return;
 
+	/*
+	 * If this is a free space inode do not take the ordered extents lockdep
+	 * map.
+	 */
+	freespace_inode = btrfs_is_free_space_inode(inode);
+
 	while (1) {
 		ordered = btrfs_lookup_first_ordered_extent(inode, (u64)-1);
 		if (!ordered)
@@ -8988,6 +8997,10 @@ void btrfs_destroy_inode(struct inode *vfs_inode)
 			btrfs_err(root->fs_info,
 				  "found ordered extent %llu %llu on inode cleanup",
 				  ordered->file_offset, ordered->num_bytes);
+
+			if (!freespace_inode)
+				btrfs_lockdep_acquire(root->fs_info, btrfs_ordered_extent);
+
 			btrfs_remove_ordered_extent(inode, ordered);
 			btrfs_put_ordered_extent(ordered);
 			btrfs_put_ordered_extent(ordered);

fs/btrfs/ordered-data.c

@@ -524,6 +524,13 @@ void btrfs_remove_ordered_extent(struct btrfs_inode *btrfs_inode,
 	struct btrfs_fs_info *fs_info = root->fs_info;
 	struct rb_node *node;
 	bool pending;
+	bool freespace_inode;
+
+	/*
+	 * If this is a free space inode the thread has not acquired the ordered
+	 * extents lockdep map.
+	 */
+	freespace_inode = btrfs_is_free_space_inode(btrfs_inode);
 
 	btrfs_lockdep_acquire(fs_info, btrfs_trans_pending_ordered);
 	/* This is paired with btrfs_add_ordered_extent. */
@@ -597,6 +604,8 @@ void btrfs_remove_ordered_extent(struct btrfs_inode *btrfs_inode,
 	}
 	spin_unlock(&root->ordered_extent_lock);
 	wake_up(&entry->wait);
+	if (!freespace_inode)
+		btrfs_lockdep_release(fs_info, btrfs_ordered_extent);
 }
 
 static void btrfs_run_ordered_extent_work(struct btrfs_work *work)
@@ -715,9 +724,16 @@ void btrfs_start_ordered_extent(struct btrfs_ordered_extent *entry, int wait)
 	u64 start = entry->file_offset;
 	u64 end = start + entry->num_bytes - 1;
 	struct btrfs_inode *inode = BTRFS_I(entry->inode);
+	bool freespace_inode;
 
 	trace_btrfs_ordered_extent_start(inode, entry);
 
+	/*
+	 * If this is a free space inode do not take the ordered extents lockdep
+	 * map.
+	 */
+	freespace_inode = btrfs_is_free_space_inode(inode);
+
 	/*
 	 * pages in the range can be dirty, clean or writeback.  We
 	 * start IO on any dirty ones so the wait doesn't stall waiting
@@ -726,6 +742,8 @@ void btrfs_start_ordered_extent(struct btrfs_ordered_extent *entry, int wait)
 	if (!test_bit(BTRFS_ORDERED_DIRECT, &entry->flags))
 		filemap_fdatawrite_range(inode->vfs_inode.i_mapping, start, end);
 	if (wait) {
+		if (!freespace_inode)
+			btrfs_might_wait_for_event(inode->root->fs_info, btrfs_ordered_extent);
 		wait_event(entry->wait, test_bit(BTRFS_ORDERED_COMPLETE,
 						 &entry->flags));
 	}