btrfs: don't loop for nowait writes when checking for cross references

When checking for delayed refs when verifying if there are cross
references for a data extent, we stop if the path has nowait set and we
can't try lock the delayed ref head's mutex, returning -EAGAIN with the
goal of making a write fallback to a blocking context. However we ignore
the -EAGAIN at btrfs_cross_ref_exist() when check_delayed_ref() returns
it, and keep looping instead of immediately returning the -EAGAIN to the
caller.

Fix this by not looping if we get -EAGAIN and we have a nowait path.

Fixes: 26ce911 ("btrfs: make can_nocow_extent nowait compatible")
CC: stable@vger.kernel.org # 6.1+
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

Author: fdmanana

fs/btrfs/extent-tree.c

@@ -2422,7 +2422,7 @@ int btrfs_cross_ref_exist(struct btrfs_root *root, u64 objectid, u64 offset,
 			goto out;
 
 		ret = check_delayed_ref(root, path, objectid, offset, bytenr);
-	} while (ret == -EAGAIN);
+	} while (ret == -EAGAIN && !path->nowait);
 
 out:
 	btrfs_release_path(path);