[PATCH 4/4] ext4: avoid dividing by 0 in mb_update_avg_fragment_size() when block bitmap corrupt

[Baokun Li]

When bb_free is not 0 but bb_fragments is 0, return directly to avoid
system crash due to division by zero.

Fixes: 83e80a6e3543 ("ext4: use buckets for cr 1 block scan instead of rbtree")
CC: stable@xxxxxxxxxxxxxxx
Signed-off-by: Baokun Li <libaokun1@xxxxxxxxxx>
---
 fs/ext4/mballoc.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
index 2fbee0f0f5c3..e2a167240335 100644
--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -845,6 +845,9 @@ mb_update_avg_fragment_size(struct super_block *sb, struct ext4_group_info *grp)
 	if (!test_opt2(sb, MB_OPTIMIZE_SCAN) || grp->bb_free == 0)
 		return;
 
+	if (unlikely(grp->bb_fragments == 0))
+		return;
+
 	new_order = mb_avg_fragment_size_order(sb,
 					grp->bb_free / grp->bb_fragments);
 	if (new_order == grp->bb_avg_fragment_size_order)
-- 
2.31.1