Messages in this thread | | | Subject | Re: [RFC PATCH v3 4/6] media: tegra: Add Tegra210 Video input driver | From | Sowjanya Komatineni <> | Date | Thu, 20 Feb 2020 09:29:19 -0800 |
| |
Sure, Will update in v4.
On 2/20/20 5:33 AM, Hans Verkuil wrote: > External email: Use caution opening links or attachments > > > (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
| |