workqueue: Only unregister a registered lockdep key

The recent change to prevent use after free and a memory leak introduced an
unconditional call to wq_unregister_lockdep() in the error handling
path. If the lockdep key had not been registered yet, then the lockdep core
emits a warning.

Only call wq_unregister_lockdep() if wq_register_lockdep() has been
called first.

Fixes: 009bb42 ("workqueue, lockdep: Fix an alloc_workqueue() error path")
Reported-by: [email protected]
Signed-off-by: Bart Van Assche <[email protected]>
Signed-off-by: Thomas Gleixner <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Tejun Heo <[email protected]>
Cc: Qian Cai <[email protected]>
Link: https://lkml.kernel.org/r/[email protected]

kernel/workqueue.c

@@ -4266,7 +4266,7 @@ struct workqueue_struct *alloc_workqueue(const char *fmt,
 	INIT_LIST_HEAD(&wq->list);
 
 	if (alloc_and_link_pwqs(wq) < 0)
-		goto err_free_wq;
+		goto err_unreg_lockdep;
 
 	if (wq_online && init_rescuer(wq) < 0)
 		goto err_destroy;
@@ -4292,9 +4292,10 @@ struct workqueue_struct *alloc_workqueue(const char *fmt,
 
 	return wq;
 
-err_free_wq:
+err_unreg_lockdep:
 	wq_unregister_lockdep(wq);
 	wq_free_lockdep(wq);
+err_free_wq:
 	free_workqueue_attrs(wq->unbound_attrs);
 	kfree(wq);
 	return NULL;