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

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Message-ID: <aa2bf24e-981a-a811-c5d8-a75f0b8f693a@acm.org>
Date:   Sun, 13 Feb 2022 15:06:39 -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 2/12/22 09:14, Tetsuo Handa wrote:
> How can reviewing all flush_workqueue(system_long_wq) calls help?

It is allowed to queue blocking actions on system_long_wq. 
flush_workqueue(system_long_wq) can make a lower layer (e.g. ib_srp) 
wait on a blocking action from a higher layer (e.g. the loop driver) and 
thereby cause a deadlock. Hence my proposal to review all 
flush_workqueue(system_long_wq) calls.

Thanks,

Bart.