btrfs: replace BUG_ON() at split_item() with proper error handling

There's no need to BUG_ON() at split_item() if the leaf does not have
enough free space for the new item, we can just return -ENOSPC since
the caller can deal with errors from split_item(). Also, as this is a
very unlikely condition to happen, because the caller has invoked
setup_leaf_for_split() before calling split_item(), surround the
condition with a WARN_ON() which makes it easier to notice this
unexpected condition and tags the if branch with 'unlikely' as well.

I've actually once hit this BUG_ON() with some incorrect code changes
I had, which was very inconvenient as it required rebooting the VM.

Reviewed-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

diff --git a/fs/btrfs/ctree.c b/fs/btrfs/ctree.c
index 190dd90a88eb533c11c1fe8a37256bd6824e92a3..a4cb4b6429870169eadbef99d359cdab4d84db0c 100644 (file)
--- a/fs/btrfs/ctree.c
+++ b/fs/btrfs/ctree.c
@@ -4000,7 +4000,12 @@ static noinline int split_item(struct btrfs_path *path,
        struct btrfs_disk_key disk_key;
 
        leaf = path->nodes[0];
-       BUG_ON(btrfs_leaf_free_space(leaf) < sizeof(struct btrfs_item));
+       /*
+        * Shouldn't happen because the caller must have previously called
+        * setup_leaf_for_split() to make room for the new item in the leaf.
+        */
+       if (WARN_ON(btrfs_leaf_free_space(leaf) < sizeof(struct btrfs_item)))
+               return -ENOSPC;
 
        orig_slot = path->slots[0];
        orig_offset = btrfs_item_offset(leaf, path->slots[0]);