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From: Hans Verkuil <hverkuil@xs4all.nl>
To: Sowjanya Komatineni <skomatineni@nvidia.com>,
	thierry.reding@gmail.com, jonathanh@nvidia.com,
	frankc@nvidia.com, helen.koike@collabora.com, sboyd@kernel.org
Cc: linux-media@vger.kernel.org, devicetree@vger.kernel.org,
	linux-clk@vger.kernel.org, linux-tegra@vger.kernel.org,
	linux-kernel@vger.kernel.org
Subject: Re: [RFC PATCH v3 4/6] media: tegra: Add Tegra210 Video input driver
Date: Thu, 20 Feb 2020 14:33:47 +0100
Message-ID: <dc592f29-3109-d10c-7df7-ffdb2755ade0@xs4all.nl> (raw)
In-Reply-To: <b301c247-537d-d78e-b057-a3225b10de7e@xs4all.nl>

(Replying to myself so I can explain this a bit more)

On 2/20/20 1:44 PM, Hans Verkuil wrote:
>> +
>> +static int tegra_csi_tpg_channels_alloc(struct tegra_csi *csi)
>> +{
>> +	struct device_node *node = csi->dev->of_node;
>> +	unsigned int port_num;
>> +	int ret;
>> +	struct tegra_csi_channel *item;
>> +	unsigned int tpg_channels = csi->soc->csi_max_channels;
>> +
>> +	/* allocate CSI channel for each CSI x2 ports */
>> +	for (port_num = 0; port_num < tpg_channels; port_num++) {
>> +		item = devm_kzalloc(csi->dev, sizeof(*item), GFP_KERNEL);
> 
> Using devm_*alloc can be dangerous. If someone unbinds the driver, then
> all memory allocated with devm_ is immediately freed. But if an application
> still has a filehandle open, then when it closes it it might still reference
> this already-freed memory.
> 
> I recommend that you avoid using devm_*alloc for media drivers.

A good test is to unbind & bind the driver:

cd /sys/devices/platform/50000000.host1x/54080000.vi/driver
echo -n 54080000.vi >unbind
echo -n 54080000.vi >bind

First just do this without the driver being used. That already
gives me 'list_del corruption' kernel messages (list debugging
is turned on in my kernel).

Note that this first test is basically identical to a rmmod/modprobe
of the driver. But when I compiled the driver as a module it didn't
create any video device nodes! Nor did I see any errors in the kernel
log. I didn't pursue this, and perhaps I did something wrong, but it's
worth taking a look at.

The next step would be to have a video node open with:

v4l2-ctl --sleep 10

then while it is sleeping unbind the driver and see what happens
when v4l2-ctl exits.

Worst case is when you are streaming:

v4l2-ctl --stream-mmap

and then unbind.

In general, the best way to get this to work correctly is:

1) don't use devm_*alloc
2) set the release callback of struct v4l2_device and do all freeing there.
3) in the platform remove() callback you call media_device_unregister()
   and video_unregister_device().

It's worth getting this right in this early stage, rather than fixing it
in the future.

Regards,

	Hans

  reply index

Thread overview: 38+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-02-14 18:23 [RFC PATCH v3 0/6] Add Tegra driver for video capture Sowjanya Komatineni
2020-02-14 18:23 ` [RFC PATCH v3 1/6] dt-bindings: clock: tegra: Add clk id for CSI TPG clock Sowjanya Komatineni
2020-02-14 18:23 ` [RFC PATCH v3 2/6] clk: tegra: Add Tegra210 CSI TPG clock gate Sowjanya Komatineni
2020-02-14 18:23 ` [RFC PATCH v3 3/6] dt-binding: tegra: Add VI and CSI bindings Sowjanya Komatineni
2020-02-18 23:15   ` Rob Herring
2020-02-19  3:28     ` Sowjanya Komatineni
2020-02-20 19:45       ` Rob Herring
2020-02-20 20:39         ` Sowjanya Komatineni
2020-02-14 18:23 ` [RFC PATCH v3 4/6] media: tegra: Add Tegra210 Video input driver Sowjanya Komatineni
2020-02-16 11:03   ` Hans Verkuil
2020-02-16 19:54     ` Sowjanya Komatineni
2020-02-16 20:11       ` Sowjanya Komatineni
2020-02-16 20:22         ` Sowjanya Komatineni
2020-02-17  8:04           ` Hans Verkuil
2020-02-18  0:59             ` Sowjanya Komatineni
2020-02-18  1:04               ` Sowjanya Komatineni
2020-02-18  3:19                 ` Sowjanya Komatineni
2020-02-19 15:08                   ` Hans Verkuil
2020-02-19 16:22                     ` Sowjanya Komatineni
2020-02-20  0:09                       ` Sowjanya Komatineni
2020-02-20  9:29                         ` Hans Verkuil
2020-02-20 16:21                           ` Sowjanya Komatineni
2020-02-20 12:44   ` Hans Verkuil
2020-02-20 13:33     ` Hans Verkuil [this message]
2020-02-20 17:29       ` Sowjanya Komatineni
2020-02-20 19:11       ` Sowjanya Komatineni
2020-02-24  4:45         ` Sowjanya Komatineni
2020-03-18 11:48           ` Hans Verkuil
2020-03-18 16:14             ` Sowjanya Komatineni
2020-03-18 16:25               ` Sowjanya Komatineni
2020-03-18 17:17                 ` Sowjanya Komatineni
2020-03-19 14:29                   ` Hans Verkuil
2020-03-19 18:49                     ` Sowjanya Komatineni
2020-02-26  4:49     ` Sowjanya Komatineni
2020-02-26  5:50       ` Sowjanya Komatineni
2020-02-14 18:23 ` [RFC PATCH v3 5/6] MAINTAINERS: Add Tegra Video driver section Sowjanya Komatineni
2020-02-14 18:23 ` [RFC PATCH v3 6/6] arm64: tegra: Add Tegra VI CSI support in device tree Sowjanya Komatineni
2020-02-17 14:26 ` [RFC PATCH v3 0/6] Add Tegra driver for video capture Hans Verkuil

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