efivarfs: use I_MUTEX_CHILD nested lock to traverse variables on resume

syzbot warns about a potential deadlock, but this is a false positive
resulting from a missing lockdep annotation: iterate_dir() locks the
parent whereas the inode_lock() it warns about locks the child, which is
guaranteed to be a different lock.

So use inode_lock_nested() instead with the appropriate lock class.

Reported-by: syzbot+019072ad24ab1d948228@syzkaller.appspotmail.com
Suggested-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>

diff --git a/fs/efivarfs/super.c b/fs/efivarfs/super.c
index 6eae8cf655c120eeb58f166e3cc373197e9e58bc..42295d04f08de9d74853d61cfe99cdf5515a461e 100644 (file)
--- a/fs/efivarfs/super.c
+++ b/fs/efivarfs/super.c
@@ -421,7 +421,7 @@ static bool efivarfs_actor(struct dir_context *ctx, const char *name, int len,
        if (err)
                size = 0;
 
-       inode_lock(inode);
+       inode_lock_nested(inode, I_MUTEX_CHILD);
        i_size_write(inode, size);
        inode_unlock(inode);