btrfs: add lockdep annotations for pending_ordered wait event

In contrast to the num_writers and num_extwriters wait events, the
condition for the pending ordered wait event is signaled in a different
context from the wait event itself. The condition signaling occurs in
btrfs_remove_ordered_extent() in fs/btrfs/ordered-data.c while the wait
event is implemented in btrfs_commit_transaction() in
fs/btrfs/transaction.c

Thus the thread signaling the condition has to acquire the lockdep map
as a reader at the start of btrfs_remove_ordered_extent() and release it
after it has signaled the condition. In this case some dependencies
might be left out due to the placement of the annotation, but it is
better than no annotation at all.
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

@@ -1099,6 +1099,7 @@ struct btrfs_fs_info {
 	struct lockdep_map btrfs_trans_num_writers_map;
 	struct lockdep_map btrfs_trans_num_extwriters_map;
 	struct lockdep_map btrfs_state_change_map[4];
+	struct lockdep_map btrfs_trans_pending_ordered_map;
 
 #ifdef CONFIG_BTRFS_FS_REF_VERIFY
 	spinlock_t ref_verify_lock;

fs/btrfs/disk-io.c

@@ -2992,6 +2992,7 @@ 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_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/ordered-data.c

@@ -525,6 +525,7 @@ void btrfs_remove_ordered_extent(struct btrfs_inode *btrfs_inode,
 	struct rb_node *node;
 	bool pending;
 
+	btrfs_lockdep_acquire(fs_info, btrfs_trans_pending_ordered);
 	/* This is paired with btrfs_add_ordered_extent. */
 	spin_lock(&btrfs_inode->lock);
 	btrfs_mod_outstanding_extents(btrfs_inode, -1);
@@ -580,6 +581,8 @@ void btrfs_remove_ordered_extent(struct btrfs_inode *btrfs_inode,
 		}
 	}
 
+	btrfs_lockdep_release(fs_info, btrfs_trans_pending_ordered);
+
 	spin_lock(&root->ordered_extent_lock);
 	list_del_init(&entry->root_extent_list);
 	root->nr_ordered_extents--;

fs/btrfs/transaction.c

@@ -2310,6 +2310,7 @@ int btrfs_commit_transaction(struct btrfs_trans_handle *trans)
 	 * transaction. Otherwise if this transaction commits before the ordered
 	 * extents complete we lose logged data after a power failure.
 	 */
+	btrfs_might_wait_for_event(fs_info, btrfs_trans_pending_ordered);
 	wait_event(cur_trans->pending_wait,
 		   atomic_read(&cur_trans->pending_ordered) == 0);