On 03/10/2015 02:29 PM, Ezequiel Garcia wrote: > > > On 03/10/2015 10:26 AM, Hans Verkuil wrote: >> On 03/10/2015 02:18 PM, Ezequiel Garcia wrote: >>> Mauro, >>> >>> Function drivers/media/usb/em28xx/em28xx-video.c:get_next_buf >>> (copy pasted below for reference) does not take the list spinlock, >>> yet it modifies the list. Is that correct? >> >> That looks wrong to me. You really need spinlocks here. >> > > OK, second question then. Is there any way to guarantee the URBs irq handler > is *not* running, when vb2_ops are called (e.g. stop_streaming)? That depends on the op. But stop_streaming is the op that is supposed to turn off the streaming (and thus the irq), so it depends on the order of how things are done in that function. > Otherwise, given stop_streaming will return the current buffer to vb2 > (dev->usb_ctl.vid_buf), I believe that will race against the irq handler, > which is processing it. > > It seems that's currently racy as well. Hmm, the stop_streaming code looks fine at first sight, but I think there is a race if you start streaming both video and vbi, and then stop streaming one of the two. I think the code might keep calling get_next_buf() in that case, even if for that stream the streaming was stopped. This is a problem anyway: get_next_buf() should do this check at the beginning: if (!vb2_start_streaming_called(vb2_queue)) return NULL; to prevent it from using buffer before start_streaming was actually called. 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
