landlock: fix splats from iput() after it started calling might_sleep()

At this point it is guaranteed this is not the last reference.

However, a recent addition of might_sleep() at top of iput() started
generating false-positives as it was executing for all values.

Remedy the problem by using the newly introduced iput_not_last().

Reported-by: [email protected]
Closes: https://lore.kernel.org/all/[email protected]/
Fixes: 2ef435a ("fs: add might_sleep() annotation to iput() and more")
Signed-off-by: Mateusz Guzik <[email protected]>
Link: https://patch.msgid.link/[email protected]
Reviewed-by: Mickaël Salaün <[email protected]>
Signed-off-by: Christian Brauner <[email protected]>

Author: mjguzik

security/landlock/fs.c

@@ -1335,11 +1335,10 @@ static void hook_sb_delete(struct super_block *const sb)
 			 * At this point, we own the ihold() reference that was
 			 * originally set up by get_inode_object() and the
 			 * __iget() reference that we just set in this loop
-			 * walk.  Therefore the following call to iput() will
-			 * not sleep nor drop the inode because there is now at
-			 * least two references to it.
+			 * walk.  Therefore there are at least two references
+			 * on the inode.
 			 */
-			iput(inode);
+			iput_not_last(inode);
 		} else {
 			spin_unlock(&object->lock);
 			rcu_read_unlock();