linux-kernel - Re: [syzbot] INFO: task hung in hci_dev_close

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Message-ID: <49e04fb8-e8fe-17d3-0b5f-e8d255010936@I-love.SAKURA.ne.jp>
Date:   Thu, 28 Jul 2022 21:25:50 +0900
From:   Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To:     Johannes Berg <johannes@...solutions.net>,
        Tejun Heo <tj@...nel.org>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        "syzkaller-bugs@...glegroups.com" <syzkaller-bugs@...glegroups.com>,
        Hillf Danton <hdanton@...a.com>,
        syzbot <syzbot+c56f6371c48cad0420f9@...kaller.appspotmail.com>
Subject: Re: [syzbot] INFO: task hung in hci_dev_close_sync

On 2022/05/04 18:24, Johannes Berg wrote:
> On Wed, 2022-05-04 at 05:12 +0000, Tetsuo Handa wrote:
>>
>> This seems to be a question regarding commit 87915adc3f0acdf0 ("workqueue: re-add lockdep dependencies for flushing").
>>>
>>> syzbot should have been able to catch cancel_work_sync() in work context
>>> by checking lockdep_map in __flush_work() for both flush and cancel.
>>>
>>> Hillf
>>>
>>> --- y/kernel/workqueue.c
>>> +++ x/kernel/workqueue.c
>>> @@ -3075,10 +3075,10 @@ static bool __flush_work(struct work_str
>>>       if (WARN_ON(!work->func))
>>>               return false;
>>>
>>> -     if (!from_cancel) {
>>> +     //if (!from_cancel) {
>>>
> 
> I think this is explained in commit d6e89786bed9 ("workqueue: skip
> lockdep wq dependency in cancel_work_sync()")

I couldn't agree on that reasoning, and I sent
https://lkml.kernel.org/r/21b9c1ac-64b7-7f4b-1e62-bf2f021fffcd@I-love.SAKURA.ne.jp .