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

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Message-ID: <71d6f14e-46af-cc5a-bc70-af1cdc6de8d5@acm.org>
Date:   Sat, 12 Feb 2022 08:37:55 -0800
From:   Bart Van Assche <bvanassche@....org>
To:     Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
        syzbot <syzbot+831661966588c802aae9@...kaller.appspotmail.com>,
        jgg@...pe.ca, linux-kernel@...r.kernel.org,
        linux-rdma@...r.kernel.org, syzkaller-bugs@...glegroups.com,
        Tejun Heo <tj@...nel.org>,
        Lai Jiangshan <jiangshanlai@...il.com>
Subject: Re: [syzbot] possible deadlock in worker_thread

On 2/11/22 21:31, Tetsuo Handa wrote:
> But this report might be suggesting us that we should consider
> deprecating (and eventually getting rid of) system-wide workqueues
> (declared in include/linux/workqueue.h), for since flush_workqueue()
> synchronously waits for completion, sharing system-wide workqueues
> among multiple modules can generate unexpected locking dependency
> chain (like this report).

I do not agree with deprecating system-wide workqueues. I think that all 
flush_workqueue(system_long_wq) calls should be reviewed since these are 
deadlock-prone.

Thanks,

Bart.