linux-kernel - Re: [PATCH v2] nbd: Don't use workqueue to handle recv work

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Message-ID: <CACycT3umMYfwVZRXinEBM=Kh+kQPYH5GBN6eKrt9unZSM8W0qw@mail.gmail.com>
Date:   Sat, 19 Feb 2022 21:04:25 +0800
From:   Yongji Xie <xieyongji@...edance.com>
To:     Josef Bacik <josef@...icpanda.com>
Cc:     Christoph Hellwig <hch@...radead.org>,
        Jens Axboe <axboe@...nel.dk>,
        Bart Van Assche <bvanassche@....org>,
        linux-block@...r.kernel.org, nbd@...er.debian.org,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] nbd: Don't use workqueue to handle recv work

On Fri, Feb 18, 2022 at 11:21 PM Josef Bacik <josef@...icpanda.com> wrote:
>
> On Tue, Feb 15, 2022 at 09:17:37PM +0800, Yongji Xie wrote:
> > Ping again.
> >
> > Hi Josef, could you take a look?
>
> Sorry Yongji this got lost.  Again in the reconnect case we're still setting up
> a long running thread, so it's not like it'll happen during a normal reclaim
> path thing, it'll be acted upon by userspace.  Thanks,
>

During creating this long running thread, we might trigger memory
reclaim since workqueue will use GFP_KERNEL allocation for it. Then a
deadlock can occur if the memory reclaim happens to hit the page cache
on this reconnecting nbd device.

Thanks,
Yongji