linux-kernel - Re: [syzbot] possible deadlock in worker

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Message-ID: <4168398.ejJDZkT8p0@leap>
Date:   Thu, 17 Feb 2022 13:27:08 +0100
From:   "Fabio M. De Francesco" <fmdefrancesco@...il.com>
To:     Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
        syzkaller-bugs@...glegroups.com
Cc:     Bart Van Assche <bvanassche@....org>,
        syzbot <syzbot+831661966588c802aae9@...kaller.appspotmail.com>,
        jgg@...pe.ca, linux-kernel@...r.kernel.org,
        linux-rdma@...r.kernel.org, syzkaller-bugs@...glegroups.com,
        Lai Jiangshan <jiangshanlai@...il.com>,
        Tejun Heo <tj@...nel.org>
Subject: Re: [syzbot] possible deadlock in worker_thread

On lunedì 14 febbraio 2022 04:44:25 CET Tejun Heo wrote:
> Hello,
> 
> On Mon, Feb 14, 2022 at 10:08:00AM +0900, Tetsuo Handa wrote:
> > +	destroy_workqueue(srp_tl_err_wq);
> > 
> > Then, we can call WARN_ON() if e.g. flush_workqueue() is called on system-wide workqueues.
> 
> Yeah, this is the right thing to do. It makes no sense at all to call
> flush_workqueue() on the shared workqueues as the caller has no idea what
> it's gonna end up waiting for. It was on my todo list a long while ago but
> slipped through the crack. If anyone wanna take a stab at it (including
> scrubbing the existing users, of course), please be my guest.
> 

Just to think and understand... what if the system-wide WQ were allocated as unbound 
ordered (i.e., as in alloc_ordered_workqueue()) with "max_active" of one?

1) Would it solve the locks dependency problem?
2) Would it introduce performance penalties (bottlenecks)?

Greetings,

Fabio

>
> Thanks.
> 
> -- 
> tejun
>