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Date: Wed, 27 Mar 2024 20:04:47 +0900
From: Sergey Senozhatsky <senozhatsky@chromium.org>
To: Ricardo Ribalda <ribalda@chromium.org>
Cc: Mauro Carvalho Chehab <mchehab@kernel.org>,
	Guenter Roeck <linux@roeck-us.net>,
	Max Staudt <mstaudt@chromium.org>, Tomasz Figa <tfiga@chromium.org>,
	Laurent Pinchart <laurent.pinchart@ideasonboard.com>,
	Alan Stern <stern@rowland.harvard.edu>,
	Hans Verkuil <hverkuil-cisco@xs4all.nl>,
	linux-media@vger.kernel.org, linux-kernel@vger.kernel.org,
	Sean Paul <seanpaul@chromium.org>,
	Sakari Ailus <sakari.ailus@linux.intel.com>
Subject: Re: [PATCH v4 0/4] uvcvideo: Attempt N to land UVC race conditions
 fixes
Message-ID: <20240327110447.GD1041856@google.com>
References: <20240327-guenter-mini-v4-0-49955c198eae@chromium.org>
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In-Reply-To: <20240327-guenter-mini-v4-0-49955c198eae@chromium.org>

On (24/03/27 08:24), Ricardo Ribalda wrote:
> Back in 2020 Guenter published a set of patches to fix some race
> conditions in UVC:
> https://lore.kernel.org/all/20200917022547.198090-5-linux@roeck-us.net/
> 
> That kind of race conditions are not only seen in UVC, but are a common
> seen in almost all the kernel, so this is what it was decided back then
> that we should try to fix them at higher levels.
> 
> After that. A lot of video_is_registered() were added to the core:
> 
> ```
> ribalda@alco:~/work/linux$ git grep is_registered drivers/media/v4l2-core/
> drivers/media/v4l2-core/v4l2-compat-ioctl32.c:  if (!video_is_registered(vdev))
> drivers/media/v4l2-core/v4l2-dev.c:     if (video_is_registered(vdev))
> drivers/media/v4l2-core/v4l2-dev.c:     if (video_is_registered(vdev))
> drivers/media/v4l2-core/v4l2-dev.c:     if (video_is_registered(vdev)) {
> drivers/media/v4l2-core/v4l2-dev.c:             if (video_is_registered(vdev))
> drivers/media/v4l2-core/v4l2-dev.c:     if (!video_is_registered(vdev))
> drivers/media/v4l2-core/v4l2-dev.c:     if (video_is_registered(vdev))
> drivers/media/v4l2-core/v4l2-dev.c:     if (vdev == NULL || !video_is_registered(vdev)) {
> drivers/media/v4l2-core/v4l2-dev.c:             if (video_is_registered(vdev))
> drivers/media/v4l2-core/v4l2-dev.c:     if (!vdev || !video_is_registered(vdev))
> drivers/media/v4l2-core/v4l2-ioctl.c:   if (!video_is_registered(vfd)) {
> drivers/media/v4l2-core/v4l2-subdev.c:  if (video_is_registered(vdev)) {
> ```
> 
> And recently Sakari is trying to land:
> https://lore.kernel.org/linux-media/20230201214535.347075-1-sakari.ailus@linux.intel.com/
> 
> Which will make obsolete a lot off (all?) of the video_is_registered() checks in
> Guenter's patches.
> 
> Besides those checks, there were some other valid races fixed in his
> patches.
> 
> This patchset tries to fix the races still present in our code.
> 
> Thanks!
> 
> Signed-off-by: Ricardo Ribalda <ribalda@chromium.org>

Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>