[alsa-devel] [PATCH] ALSA: snd_usb_caiaq: track submitted output urbs

[Daniel Mack]

The snd_usb_caiaq driver currently assumes that output urbs are serviced
in time and doesn't track when and whether they are given back by the
USB core. That usually works fine, but due to temporary limitations of
the XHCI stack, we faced that urbs were submitted more than once with
this approach.

As it's no good practice to fire and forget urbs anyway, this patch
introduces a proper bit mask to track which requests have been submitted
and given back.

That alone however doesn't make the driver work in case the host
controller is broken and doesn't give back urbs at all, and the output
stream will stop once all pre-allocated output urbs are consumed. But
it does prevent crashes of the controller stack in such cases.

See http://bugzilla.kernel.org/show_bug.cgi?id=40702 for more details.

Signed-off-by: Daniel Mack <zonque at gmail.com>
Reported-and-tested-by: Matej Laitl <matej at laitl.cz>
Cc: Sarah Sharp <sarah.a.sharp at linux.intel.com>
Cc: stable at kernel.org
---
 sound/usb/caiaq/audio.c  |   31 +++++++++++++++++++++++++++----
 sound/usb/caiaq/device.h |    1 +
 2 files changed, 28 insertions(+), 4 deletions(-)

diff --git a/sound/usb/caiaq/audio.c b/sound/usb/caiaq/audio.c
index aa52b3e..2cf87f5 100644
--- a/sound/usb/caiaq/audio.c
+++ b/sound/usb/caiaq/audio.c
@@ -139,8 +139,12 @@ static void stream_stop(struct snd_usb_caiaqdev *dev)
 
 	for (i = 0; i < N_URBS; i++) {
 		usb_kill_urb(dev->data_urbs_in[i]);
-		usb_kill_urb(dev->data_urbs_out[i]);
+
+		if (test_bit(i, &dev->outurb_active_mask))
+			usb_kill_urb(dev->data_urbs_out[i]);
 	}
+
+	dev->outurb_active_mask = 0;
 }
 
 static int snd_usb_caiaq_substream_open(struct snd_pcm_substream *substream)
@@ -612,8 +616,8 @@ static void read_completed(struct urb *urb)
 {
 	struct snd_usb_caiaq_cb_info *info = urb->context;
 	struct snd_usb_caiaqdev *dev;
-	struct urb *out;
-	int frame, len, send_it = 0, outframe = 0;
+	struct urb *out = NULL;
+	int i, frame, len, send_it = 0, outframe = 0;
 	size_t offset = 0;
 
 	if (urb->status || !info)
@@ -624,7 +628,17 @@ static void read_completed(struct urb *urb)
 	if (!dev->streaming)
 		return;
 
-	out = dev->data_urbs_out[info->index];
+	/* find an unused output urb that is unused */
+	for (i = 0; i < N_URBS; i++)
+		if (test_and_set_bit(i, &dev->outurb_active_mask) == 0) {
+			out = dev->data_urbs_out[i];
+			break;
+		}
+
+	if (!out) {
+		log("Unable to find an output urb to use\n");
+		goto requeue;
+	}
 
 	/* read the recently received packet and send back one which has
 	 * the same layout */
@@ -655,8 +669,12 @@ static void read_completed(struct urb *urb)
 		out->number_of_packets = outframe;
 		out->transfer_flags = URB_ISO_ASAP;
 		usb_submit_urb(out, GFP_ATOMIC);
+	} else {
+		struct snd_usb_caiaq_cb_info *oinfo = out->context;
+		clear_bit(oinfo->index, &dev->outurb_active_mask);
 	}
 
+requeue:
 	/* re-submit inbound urb */
 	for (frame = 0; frame < FRAMES_PER_URB; frame++) {
 		urb->iso_frame_desc[frame].offset = BYTES_PER_FRAME * frame;
@@ -678,6 +696,8 @@ static void write_completed(struct urb *urb)
 		dev->output_running = 1;
 		wake_up(&dev->prepare_wait_queue);
 	}
+
+	clear_bit(info->index, &dev->outurb_active_mask);
 }
 
 static struct urb **alloc_urbs(struct snd_usb_caiaqdev *dev, int dir, int *ret)
@@ -829,6 +849,9 @@ int snd_usb_caiaq_audio_init(struct snd_usb_caiaqdev *dev)
 	if (!dev->data_cb_info)
 		return -ENOMEM;
 
+	dev->outurb_active_mask = 0;
+	BUILD_BUG_ON(N_URBS > (sizeof(dev->outurb_active_mask) * 8));
+
 	for (i = 0; i < N_URBS; i++) {
 		dev->data_cb_info[i].dev = dev;
 		dev->data_cb_info[i].index = i;
diff --git a/sound/usb/caiaq/device.h b/sound/usb/caiaq/device.h
index b2b3101..3f9c633 100644
--- a/sound/usb/caiaq/device.h
+++ b/sound/usb/caiaq/device.h
@@ -96,6 +96,7 @@ struct snd_usb_caiaqdev {
 	int input_panic, output_panic, warned;
 	char *audio_in_buf, *audio_out_buf;
 	unsigned int samplerates, bpp;
+	unsigned long outurb_active_mask;
 
 	struct snd_pcm_substream *sub_playback[MAX_STREAMS];
 	struct snd_pcm_substream *sub_capture[MAX_STREAMS];
-- 
1.7.6