Btrfs: cleanup BUG_ON in merge_bio

One can use btrfs-corrupt-block to hit BUG_ON() in merge_bio(),
thus this aims to stop anyone to panic the whole system by using
 their btrfs.

Since the error in merge_bio can only come from __btrfs_map_block()
when chunk tree mapping has something insane and __btrfs_map_block()
has already had printed the reason, we can just return errors in
merge_bio.

Signed-off-by: Liu Bo <bo.li.liu@oracle.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

2 files changed, 6 insertions, 3 deletions

diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
index 9aaa544e65a9..ea12d0ee684f 100644
--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -2756,7 +2756,6 @@ static int merge_bio(int rw, struct extent_io_tree *tree, struct page *page,
         if (tree->ops && tree->ops->merge_bio_hook)
                 ret = tree->ops->merge_bio_hook(rw, page, offset, size, bio,
                                                 bio_flags);
-        BUG_ON(ret < 0);
         return ret;
 
 }
diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 01c6fca925f7..f935fad17838 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -1822,6 +1822,10 @@ static void btrfs_clear_bit_hook(struct inode *inode,
 /*
  * extent_io.c merge_bio_hook, this must check the chunk tree to make sure
  * we don't create bios that span stripes or chunks
+ *
+ * return 1 if page cannot be merged to bio
+ * return 0 if page can be merged to bio
+ * return error otherwise
  */
 int btrfs_merge_bio_hook(int rw, struct page *page, unsigned long offset,
                          size_t size, struct bio *bio,
@@ -1840,8 +1844,8 @@ int btrfs_merge_bio_hook(int rw, struct page *page, unsigned long offset,
         map_length = length;
         ret = btrfs_map_block(root->fs_info, rw, logical,
                               &map_length, NULL, 0);
-        /* Will always return 0 with map_multi == NULL */
-        BUG_ON(ret < 0);
+        if (ret < 0)
+                return ret;
         if (map_length < length + size)
                 return 1;
         return 0;