linux-kernel - [PATCH] kernel/workqueue: Only unregister a lockdep key if it has been registered first

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Date:   Mon, 11 Mar 2019 16:02:55 -0700
From:   Bart Van Assche <bvanassche@....org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Ingo Molnar <mingo@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        linux-kernel@...r.kernel.org, Bart Van Assche <bvanassche@....org>,
        Tejun Heo <tj@...nel.org>, Qian Cai <cai@....pw>,
        syzbot+be0c198232f86389c3dd@...kaller.appspotmail.com
Subject: [PATCH] kernel/workqueue: Only unregister a lockdep key if it has been registered first

Only call wq_unregister_lockdep() if wq_register_lockdep() has been
called first. This patch avoids that the following warning is reported:

WARNING: CPU: 1 PID: 6970 at kernel/locking/lockdep.c:4925 lockdep_unregister_key+0x21c/0x4e0

That warning refers to the following source code statement:

	WARN_ON_ONCE(!found);

Cc: Tejun Heo <tj@...nel.org>
Cc: Qian Cai <cai@....pw>
Reported-by: syzbot+be0c198232f86389c3dd@...kaller.appspotmail.com
Fixes: 009bb421b6ce ("workqueue, lockdep: Fix an alloc_workqueue() error path")
Signed-off-by: Bart Van Assche <bvanassche@....org>
---
 kernel/workqueue.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 4026d1871407..ddee541ea97a 100644
--- a/kernel/workqueue.c
+++ b/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;
-- 
2.21.0