On 03/10/2015 03:06 PM, Ezequiel Garcia wrote: > > > On 03/10/2015 10:46 AM, Hans Verkuil wrote: >> 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. >> > > Ah, right. As long as you kill the urbs before you try to access the > current buffer, everything is OK. > >>> 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. >> > > I'd say get_next_buf() is called only in the URB complete handler path, > and hence only after start_streaming. Well, no. If you are streaming just video and then start streaming vbi in addition to the video, then I think get_next_buf() can be called for the VBI stream before start_streaming is called for that VBI stream. Hans > However, maybe there's a subtle > issue here: URB complete handler can be called _while_ start_streaming > is still running. > -- 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
