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

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Message-ID: <54cfa5a5-558d-463c-7131-9b56410403cc@xs4all.nl>
Date:   Fri, 18 Feb 2022 09:03:05 +0100
From:   Hans Verkuil <hverkuil@...all.nl>
To:     Dongliang Mu <mudongliangabcd@...il.com>
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 18/02/2022 06:58, Dongliang Mu wrote:
> 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?

No, flush_work already checks if there is anything to do. If nothing was
scheduled, it will just return.

Regards,

	Hans

> 
>>
>> Can you try that?
> 
> 
>>
>> Regards,
>>
>>         Hans
>>
>>>       mutex_lock(&dev->io_mutex);
>>>       hdpvr_cancel_queue(dev);
>>>       mutex_unlock(&dev->io_mutex);
>>