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

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Message-ID: <06b2f59c-3c96-9443-7a23-f1c957a41d9b@I-love.SAKURA.ne.jp>
Date:   Wed, 16 Feb 2022 07:05:05 +0900
From:   Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To:     Bart Van Assche <bvanassche@....org>,
        Haakon Bugge <haakon.bugge@...cle.com>
Cc:     Tejun Heo <tj@...nel.org>,
        syzbot <syzbot+831661966588c802aae9@...kaller.appspotmail.com>,
        Jason Gunthorpe <jgg@...pe.ca>,
        LKML <linux-kernel@...r.kernel.org>,
        OFED mailing list <linux-rdma@...r.kernel.org>,
        "syzkaller-bugs@...glegroups.com" <syzkaller-bugs@...glegroups.com>,
        Lai Jiangshan <jiangshanlai@...il.com>
Subject: Re: [syzbot] possible deadlock in worker_thread

On 2022/02/16 2:05, Bart Van Assche wrote:
> On 2/15/22 04:48, Tetsuo Handa wrote:
>> I do not want to do like
>>
>> -    system_wq = alloc_workqueue("events", 0, 0);
>> +    system_wq = alloc_workqueue("events", __WQ_SYSTEM_WIDE, 0);
>>
>> because the intent of this change is to ask developers to create their own WQs.
> 
> I want more developers to use the system-wide workqueues since that reduces memory usage. That matters for embedded devices running Linux.

Reserving a kernel thread for WQ_MEM_RECLAIM WQ might consume some memory,
but I don't think that creating a !WQ_MEM_RECLAIM WQ consumes much memory.