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 [thread overview]
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
next prev parent reply other threads:[~2020-02-20 13:33 UTC|newest]
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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