linux-kernel - Re: [PATCH v3 2/3] media: uvcvideo: Do not halt the device after disconnect

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Date:   Wed, 22 Nov 2023 10:55:16 +0100
From:   Ricardo Ribalda <ribalda@...omium.org>
To:     Sergey Senozhatsky <senozhatsky@...omium.org>
Cc:     Mauro Carvalho Chehab <mchehab@...nel.org>,
        Guenter Roeck <linux@...ck-us.net>,
        Tomasz Figa <tfiga@...omium.org>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Alan Stern <stern@...land.harvard.edu>,
        Hans Verkuil <hverkuil-cisco@...all.nl>,
        linux-media@...r.kernel.org, linux-kernel@...r.kernel.org,
        Sean Paul <seanpaul@...omium.org>,
        Sakari Ailus <sakari.ailus@...ux.intel.com>
Subject: Re: [PATCH v3 2/3] media: uvcvideo: Do not halt the device after disconnect

Hi Sergey

On Wed, 22 Nov 2023 at 09:01, Sergey Senozhatsky
<senozhatsky@...omium.org> wrote:
>
> On (23/11/22 16:47), Sergey Senozhatsky wrote:
> > Can the following happen?
>
> Consider the following case (when CPU1 experienced a delay, a preemption
> or anything):
>
> > CPU0                                            CPU1
> >  uvc_disconnect()
> >                                               uvc_video_stop_streaming()
> >  usb_set_intfdata()
> >  uvc_unregister_video()
> >
> >                                               if (!smp_load(&dev->disconnected))
> >
> >  smp_store_release(&dev->disconnected, true);
> >
> >  kref_put(&dev->ref, uvc_delete);
>
> >                                                       uvc_video_halt()
>
> That uvc_video_halt() cannot be legal, right?

This patch only takes care of calls to uvc_video_stop_streaming()
after .disconnect.

Guenter's patch from this series should take care of the concurrent
calls. I will resend making it explicit.

Thanks!


-- 
Ricardo Ribalda