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Subject: Re: [PATCH 0/2] Use Media Dev Allocator to fix vimc dev lifetime bugs
To:     helen.koike@collabora.com
Cc:     Shuah Khan <skhan@linuxfoundation.org>,
        linux-media@vger.kernel.org, linux-kernel@vger.kernel.org
References: <cover.1558667245.git.skhan@linuxfoundation.org>
From:   Hans Verkuil <hverkuil-cisco@xs4all.nl>
Message-ID: <c9160fe7-e880-4070-3959-b9e9177acf54@xs4all.nl>
Date:   Thu, 13 Jun 2019 07:44:15 +0200
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On 5/24/19 5:31 AM, Shuah Khan wrote:
> media_device is embedded in struct vimc_device and when vimc is removed
> vimc_device and the embedded media_device goes with it, while the active
> stream and vimc_capture continue to access it.
> 
> Fix the media_device lifetime problem by changing vimc to create shared
> media_device using Media Device Allocator API and vimc_capture getting
> a reference to vimc module. With this change, vimc module can be removed
> only when the references are gone. vimc can be removed after vimc_capture
> is removed.
> 
> Media Device Allocator API supports just USB devices. Enhance it
> adding a genetic device allocate interface to support other media
> drivers.
> 
> The new interface takes pointer to struct device instead and creates
> media device. This interface allows a group of drivers that have a
> common root device to share media device resource and ensure media
> device doesn't get deleted as long as one of the drivers holds its
> reference.
> 
> The new interface has been tested with vimc component driver to fix
> panics when vimc module is removed while streaming is in progress.

Helen, can you review this series? I'm not sure this is the right approach
for a driver like vimc, and even if it is, then it is odd that vimc-capture
is the only vimc module that's handled here.

My gut feeling is that this should be handled inside vimc directly and not
using the media-dev-allocator.

Regards,

	Hans

> 
> Shuah Khan (2):
>   media: add generic device allocate interface to media-dev-allocator
>   vimc: fix BUG: unable to handle kernel NULL pointer dereference
> 
>  drivers/media/Makefile                     |  4 +-
>  drivers/media/media-dev-allocator.c        | 39 ++++++++++++++
>  drivers/media/platform/vimc/vimc-capture.c | 17 +++++-
>  drivers/media/platform/vimc/vimc-core.c    | 60 ++++++++++++----------
>  include/media/media-dev-allocator.h        | 46 ++++++++++++++---
>  5 files changed, 130 insertions(+), 36 deletions(-)
>