At Wed, 7 Nov 2012 12:34:43 -0500 (EST), Alan Stern wrote: > > On Mon, 5 Nov 2012, Christof Meerwald wrote: > > > BTW, I have been able to reproduce the problem on a completely > > different machine (also running Ubuntu 12.10, but different hardware). > > The important thing appears to be that the USB audio device is > > connected via a USB 2.0 hub (and then using the test code posted in > > http://pastebin.com/aHGe1S1X specifying the audio device as > > "plughw:Set" (or whatever it's called) seems to trigger the freeze). > > Christof: Thank you for that reference, it was a big help. After > crashing my system many times I have tracked the problem, at least in > part. The patch below should prevent your system from freezing. > > > Takashi: It turns out the the problem is triggered when the audio > subsystem calls snd_usb_endpoint_stop() with wait == 0 and then calls > snd_usb_endpoint_start(). Since the driver doesn't wait for the > outstanding URBs to finish, it tries to submit them again while they > are still active. > > Normally the USB core would realize this and fail the submission, but a > bug in ehci-hcd prevented this from happening. (That bug is what the > patch below fixes.) The URB gets added to the active list twice, > resulting in list corruption and an oops in interrupt context, which > freezes the system. > > The user program that triggers the problem basically looks like this: > > snd_pcm_prepare(rec_pcm); > snd_pcm_start(rec_pcm); > snd_pcm_drop(rec_pcm); > > snd_pcm_prepare(rec_pcm); > snd_pcm_start(rec_pcm); > > The snd_pcm_drop call unlinks the URBs but does not wait for them to > finish. Then the second snd_pcm_start call submits the URBs before > they have finished. > > What is the right solution for this problem? How about the patch below? (It's for 3.6, and won't be applied cleanly to 3.7, but easy to adapt.) Takashi --- diff --git a/sound/usb/endpoint.c b/sound/usb/endpoint.c index d9de667..38830e2 100644 --- a/sound/usb/endpoint.c +++ b/sound/usb/endpoint.c @@ -35,6 +35,7 @@ #define EP_FLAG_ACTIVATED 0 #define EP_FLAG_RUNNING 1 +#define EP_FLAG_STOPPING 2 /* * snd_usb_endpoint is a model that abstracts everything related to an @@ -502,10 +503,19 @@ static int wait_clear_urbs(struct snd_usb_endpoint *ep) if (alive) snd_printk(KERN_ERR "timeout: still %d active urbs on EP #%x\n", alive, ep->ep_num); + clear_bit(EP_FLAG_STOPPING, &ep->flags); return 0; } +/* wait until urbs are really dropped */ +void snd_usb_endpoint_sync_stop(struct snd_usb_endpoint *ep) +{ + if (test_bit(EP_FLAG_STOPPING, &ep->flags)) + wait_clear_urbs(ep); +} + + /* * unlink active urbs. */ @@ -913,6 +923,8 @@ void snd_usb_endpoint_stop(struct snd_usb_endpoint *ep, if (wait) wait_clear_urbs(ep); + else + set_bit(EP_FLAG_STOPPING, &ep->flags); } } diff --git a/sound/usb/endpoint.h b/sound/usb/endpoint.h index cbbbdf2..c1540a4 100644 --- a/sound/usb/endpoint.h +++ b/sound/usb/endpoint.h @@ -16,6 +16,7 @@ int snd_usb_endpoint_set_params(struct snd_usb_endpoint *ep, int snd_usb_endpoint_start(struct snd_usb_endpoint *ep, int can_sleep); void snd_usb_endpoint_stop(struct snd_usb_endpoint *ep, int force, int can_sleep, int wait); +void snd_usb_endpoint_sync_stop(struct snd_usb_endpoint *ep); int snd_usb_endpoint_activate(struct snd_usb_endpoint *ep); int snd_usb_endpoint_deactivate(struct snd_usb_endpoint *ep); void snd_usb_endpoint_free(struct list_head *head); diff --git a/sound/usb/pcm.c b/sound/usb/pcm.c index f782ce1..aee3ab0 100644 --- a/sound/usb/pcm.c +++ b/sound/usb/pcm.c @@ -546,6 +546,11 @@ static int snd_usb_pcm_prepare(struct snd_pcm_substream *substream) if (snd_BUG_ON(!subs->data_endpoint)) return -EIO; + if (subs->sync_endpoint) + snd_usb_endpoint_sync_stop(subs->sync_endpoint); + if (subs->data_endpoint) + snd_usb_endpoint_sync_stop(subs->data_endpoint); + /* some unit conversions in runtime */ subs->data_endpoint->maxframesize = bytes_to_frames(runtime, subs->data_endpoint->maxpacksize); -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
