bcachefs: Fix accidental O(n^2) in fiemap

Since bch2_seek_pagecache_data() searches for dirty data, we only want
to call it for holes in the extents btree - otherwise we have an
accidental O(n^2), as we repeatedly search the same range.

Reported-by: Marcin Mirosław <marcin@mejor.pl>
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

diff --git a/fs/bcachefs/fs.c b/fs/bcachefs/fs.c
index b6801861c66f1c4322d777e5534c822af038f214..4b742e62255bb788229c61378082abeaf0d57a6d 100644 (file)
--- a/fs/bcachefs/fs.c
+++ b/fs/bcachefs/fs.c
@@ -1429,7 +1429,9 @@ static int bch2_next_fiemap_extent(struct btree_trans *trans,
        if (ret)
                goto err;
 
-       ret = bch2_next_fiemap_pagecache_extent(trans, inode, start, end, cur);
+       u64 pagecache_end = k.k ? max(start, bkey_start_offset(k.k)) : end;
+
+       ret = bch2_next_fiemap_pagecache_extent(trans, inode, start, pagecache_end, cur);
        if (ret)
                goto err;