linux-kernel - Re: [PATCH] media: hdpvr: call flush

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Message-ID: <CAD-N9QXyU+yGU15yJnnU=JOjKGFDfjY03xk70pHgx88BcBPASA@mail.gmail.com>
Date:   Fri, 18 Feb 2022 13:58:16 +0800
From:   Dongliang Mu <mudongliangabcd@...il.com>
To:     Hans Verkuil <hverkuil@...all.nl>
Cc:     Dongliang Mu <dzm91@...t.edu.cn>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        syzkaller <syzkaller@...glegroups.com>,
        linux-media@...r.kernel.org,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] media: hdpvr: call flush_work only if initialized

On Thu, Feb 17, 2022 at 8:05 PM Hans Verkuil <hverkuil@...all.nl> wrote:
>
> On 17/02/2022 05:39, Dongliang Mu wrote:
> > From: Dongliang Mu <mudongliangabcd@...il.com>
> >
> > flush_work will throw one WARN if worker->func is NULL. So we should always
> > initialize one worker before calling flush_work. When hdpvr_probe does not
> > initialize its worker, the hdpvr_disconnect will encounter one WARN. The
> > stack trace is in the following:
> >
> >  hdpvr_disconnect+0xb8/0xf2 drivers/media/usb/hdpvr/hdpvr-core.c:425
> >  usb_unbind_interface+0xbf/0x3a0 drivers/usb/core/driver.c:458
> >  __device_release_driver drivers/base/dd.c:1206 [inline]
> >  device_release_driver_internal+0x22a/0x230 drivers/base/dd.c:1237
> >  bus_remove_device+0x108/0x160 drivers/base/bus.c:529
> >  device_del+0x1fe/0x510 drivers/base/core.c:3592
> >  usb_disable_device+0xd1/0x1d0 drivers/usb/core/message.c:1419
> >  usb_disconnect+0x109/0x330 drivers/usb/core/hub.c:2228
> >
> > Fix this by adding a sanity check of the worker before flush_work.
> >
> > Reported-by: syzkaller <syzkaller@...glegroups.com>
> > Signed-off-by: Dongliang Mu <mudongliangabcd@...il.com>
> > ---
> >  drivers/media/usb/hdpvr/hdpvr-core.c | 3 ++-
> >  1 file changed, 2 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/media/usb/hdpvr/hdpvr-core.c b/drivers/media/usb/hdpvr/hdpvr-core.c
> > index 52e05a69c46e..d102b459d45d 100644
> > --- a/drivers/media/usb/hdpvr/hdpvr-core.c
> > +++ b/drivers/media/usb/hdpvr/hdpvr-core.c
> > @@ -422,7 +422,8 @@ static void hdpvr_disconnect(struct usb_interface *interface)
> >       mutex_unlock(&dev->io_mutex);
> >       v4l2_device_disconnect(&dev->v4l2_dev);
> >       msleep(100);
> > -     flush_work(&dev->worker);
> > +     if (dev->worker.func)
> > +             flush_work(&dev->worker);
>
> I don't think this is the right fix. Instead, move the INIT_WORK line from
> hdpvr_start_streaming() to hdpvr_register_videodev(). That should initialize
> the worker struct from the start instead of only when you start streaming,
> as is the case today.

I see your point.

One small question: if we initialize worker at the beginning of
hdpvr_register_videodev, but without schedule_work, will flush_work at
hdpvr_disconnect lead to some issues?

Or we need to verify if the work is pending or running at hdpvr_disconnect?

>
> Can you try that?


>
> Regards,
>
>         Hans
>
> >       mutex_lock(&dev->io_mutex);
> >       hdpvr_cancel_queue(dev);
> >       mutex_unlock(&dev->io_mutex);
>