Btrfs: fix data allocation hint start

[cascardo/linux.git] / fs / btrfs / inode.c

diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 78139ef..d8393dd 100644 (file)
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -743,8 +743,22 @@ static noinline int cow_file_range(struct inode *inode,
        em = search_extent_mapping(&BTRFS_I(inode)->extent_tree,
                                   start, num_bytes);
        if (em) {
-               alloc_hint = em->block_start;
-               free_extent_map(em);
+               /*
+                * if block start isn't an actual block number then find the
+                * first block in this inode and use that as a hint.  If that
+                * block is also bogus then just don't worry about it.
+                */
+               if (em->block_start >= EXTENT_MAP_LAST_BYTE) {
+                       free_extent_map(em);
+                       em = search_extent_mapping(em_tree, 0, 0);
+                       if (em && em->block_start < EXTENT_MAP_LAST_BYTE)
+                               alloc_hint = em->block_start;
+                       if (em)
+                               free_extent_map(em);
+               } else {
+                       alloc_hint = em->block_start;
+                       free_extent_map(em);
+               }
        }
        read_unlock(&BTRFS_I(inode)->extent_tree.lock);
        btrfs_drop_extent_cache(inode, start, start + num_bytes - 1, 0);