ext4: Fix lockdep recursive locking warning From: "Aneesh Kumar K.V" In ext4_mb_init_group(), if the filesystem block size is less than PAGE_SIZE/2, the code tries to grab alloc_sem for multiple block groups in a loop. We need to allow for this by using down_write_nested() and passing in the loop index as a lock subclass number. This works because no other code path needs to take multiple alloc_sem's. Note that lockdep will fail for filesystem blocksize smaller than to PAGE_SIZE/16k. (e.g., a 1k filesystem blocksize with a 32k page size, or a 2k filesystem blocksize with a 64k blocksize, etc.) Signed-off-by: Aneesh Kumar K.V Signed-off-by: "Theodore Ts'o" --- diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c index 1fa311c..891ce41 100644 --- a/fs/ext4/mballoc.c +++ b/fs/ext4/mballoc.c @@ -1783,7 +1783,7 @@ static int ext4_mb_init_group(struct super_block *sb, ext4_group_t group) * no block allocation going on in any * of that groups */ - down_write(&grp->alloc_sem); + down_write_nested(&grp->alloc_sem, i); } /* * make sure we look at only those groups