If call read_mmp_block failed then s_mmp_bh will be freed in read_mmp_block.
Kmmpd wait to be killed, ext4_stop_mmpd stop kmmpd and also release s_mmp_bh.
To avoid double free, just set EXT4_SB(sb)->s_mmp_bh with NULL.

Signed-off-by: Ye Bin <redacted>
---
 fs/ext4/mmp.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/fs/ext4/mmp.c b/fs/ext4/mmp.c
index 2a1473e4a9de..eed854bb6194 100644
--- a/fs/ext4/mmp.c
+++ b/fs/ext4/mmp.c

@@ -218,6 +218,7 @@ static int kmmpd(void *data)
 				ext4_error_err(sb, -retval,
 					       "error reading MMP data: %d",
 					       retval);
+				EXT4_SB(sb)->s_mmp_bh = NULL;
 				goto wait_to_exit;
 			}
 

-- 
2.31.1