Hello Hans, On 15.12.2014 17:01, Hans Verkuil wrote: > On 12/15/2014 04:47 PM, Florian Echtler wrote: >> However, I'm running into an issue I have a hard time understanding. In >> particular, as soon as I load the kernel module, I'm getting a kernel >> oops (NULL pointer dereference) in line 354 or 355 of the attached >> source code. The reason is probably that the previous check (in line >> 350) doesn't abort - even though I didn't actually provide a buffer, so >> the list_head should be empty. As no user space program has actually >> opened the video device yet, there shouldn't be any buffers queued, >> right? (AFAICT the list is initialized properly in line 490). >> I'd be quite grateful if somebody with more experience can look over the >> code and tell me what mistakes I made :-) First of all, thanks for the quick feedback. > Why on earth is sur40_poll doing anything with video buffers? That's > all handled by vb2. As far as I can tell you can just delete everything > from '// deal with video data here' until the end of the poll function. Right now, the code doesn't do anything, but I'm planning to add the actual data retrieval at this point later. I'd like to use the input_polldev thread for this, as a) the video data should be fetched synchronously with the input device data and b) the thread will be running continuously anyway. > The probably cause of the crash here is that the input device node is > created before the 'INIT_LIST_HEAD(&sur40->buf_list);' call, and since > udevd (I think) opens new devices immediately after they are created > it is likely that sur40_poll is called before buf_list is initialized. OK, that sounds plausible, will test that tomorrow. > But, as I said, that code doesn't belong there at all, so just remove it. See above - that was actually intentional. It's kind of a hackish solution, but for the moment, I'd just like to get a video stream with minimal overhead, so I'm reusing the polldev thread. Best regards, Florian -- SENT FROM MY DEC VT50 TERMINAL
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