On 12/15/2014 11:15 PM, Florian Echtler wrote: > 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. Ah, now I see it. > >> 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. OK. If you are planning to upstream this driver, then this probably needs another look. Regards, Hans -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
