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);
--
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