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ALSA: usb-audio: Fix irq/process data synchronization 

Commit 16200948d8 ("ALSA: usb-audio: Fix race at stopping the stream") was
incomplete causing another more severe kernel panic, so it got reverted.
This fixes both the original problem and its fallout kernel race/crash.

The original fix is to move the endpoint member NULL clearing logic inside
wait_clear_urbs() so the irq triggering the urb completion doesn't call
retire_capture/playback_urb() after the NULL clearing and generate a panic.

However this creates a new race between snd_usb_endpoint_start()'s call
to wait_clear_urbs() and the irq urb completion handler which again calls
retire_capture/playback_urb() leading to a new NULL dereference.

We keep the EP deactivation code in snd_usb_endpoint_start() because
removing it will break the EP reference counting (see [1] [2] for info),
however we don't need the "can_sleep" mechanism anymore because a new
function was introduced (snd_usb_endpoint_sync_pending_stop()) which
synchronizes pending stops and gets called inside the pcm prepare callback.

It also makes sense to remove can_sleep because it was also removed from
deactivate_urbs() signature in [3] so we benefit from more simplification.

[1] commit 015618b90 ("ALSA: snd-usb: Fix URB cancellation at stream start")
[2] commit e9ba389c5 ("ALSA: usb-audio: Fix scheduling-while-atomic bug in PCM capture stream")
[3] commit ccc1696d5 ("ALSA: usb-audio: simplify endpoint deactivation code")

Fixes: f8114f8583 ("Revert "ALSA: usb-audio: Fix race at stopping the stream"")

Signed-off-by: Ioan-Adrian Ratiu <adi@adirat.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
This commit is contained in:
Ioan-Adrian Ratiu 2017-01-05 00:37:46 +02:00 committed by Takashi Iwai
parent c7efff9284
commit 1d0f953086
3 changed files with 13 additions and 16 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

17
sound/usb/endpoint.c
View File

@ -534,6 +534,11 @@ static int wait_clear_urbs(struct snd_usb_endpoint *ep)
alive, ep->ep_num);
clear_bit(EP_FLAG_STOPPING, &ep->flags);
ep->data_subs = NULL;
ep->sync_slave = NULL;
ep->retire_data_urb = NULL;
ep->prepare_data_urb = NULL;
return 0;
}
@ -912,9 +917,7 @@ int snd_usb_endpoint_set_params(struct snd_usb_endpoint *ep,
/**
* snd_usb_endpoint_start: start an snd_usb_endpoint
*
* @ep: the endpoint to start
* @can_sleep: flag indicating whether the operation is executed in
* non-atomic context
* @ep: the endpoint to start
*
* A call to this function will increment the use count of the endpoint.
* In case it is not already running, the URBs for this endpoint will be
@ -924,7 +927,7 @@ int snd_usb_endpoint_set_params(struct snd_usb_endpoint *ep,
*
* Returns an error if the URB submission failed, 0 in all other cases.
*/
int snd_usb_endpoint_start(struct snd_usb_endpoint *ep, bool can_sleep)
int snd_usb_endpoint_start(struct snd_usb_endpoint *ep)
{
int err;
unsigned int i;
@ -938,8 +941,6 @@ int snd_usb_endpoint_start(struct snd_usb_endpoint *ep, bool can_sleep)
/* just to be sure */
deactivate_urbs(ep, false);
if (can_sleep)
wait_clear_urbs(ep);
ep->active_mask = 0;
ep->unlink_mask = 0;
@ -1020,10 +1021,6 @@ void snd_usb_endpoint_stop(struct snd_usb_endpoint *ep)
if (--ep->use_count == 0) {
deactivate_urbs(ep, false);
ep->data_subs = NULL;
ep->sync_slave = NULL;
ep->retire_data_urb = NULL;
ep->prepare_data_urb = NULL;
set_bit(EP_FLAG_STOPPING, &ep->flags);
}
}

2
sound/usb/endpoint.h
View File

@ -18,7 +18,7 @@ int snd_usb_endpoint_set_params(struct snd_usb_endpoint *ep,
struct audioformat *fmt,
struct snd_usb_endpoint *sync_ep);
int snd_usb_endpoint_start(struct snd_usb_endpoint *ep, bool can_sleep);
int snd_usb_endpoint_start(struct snd_usb_endpoint *ep);
void snd_usb_endpoint_stop(struct snd_usb_endpoint *ep);
void snd_usb_endpoint_sync_pending_stop(struct snd_usb_endpoint *ep);
int snd_usb_endpoint_activate(struct snd_usb_endpoint *ep);

10
sound/usb/pcm.c
View File

@ -218,7 +218,7 @@ int snd_usb_init_pitch(struct snd_usb_audio *chip, int iface,
}
}
static int start_endpoints(struct snd_usb_substream *subs, bool can_sleep)
static int start_endpoints(struct snd_usb_substream *subs)
{
int err;
@ -231,7 +231,7 @@ static int start_endpoints(struct snd_usb_substream *subs, bool can_sleep)
dev_dbg(&subs->dev->dev, "Starting data EP @%p\n", ep);
ep->data_subs = subs;
err = snd_usb_endpoint_start(ep, can_sleep);
err = snd_usb_endpoint_start(ep);
if (err < 0) {
clear_bit(SUBSTREAM_FLAG_DATA_EP_STARTED, &subs->flags);
return err;
@ -260,7 +260,7 @@ static int start_endpoints(struct snd_usb_substream *subs, bool can_sleep)
dev_dbg(&subs->dev->dev, "Starting sync EP @%p\n", ep);
ep->sync_slave = subs->data_endpoint;
err = snd_usb_endpoint_start(ep, can_sleep);
err = snd_usb_endpoint_start(ep);
if (err < 0) {
clear_bit(SUBSTREAM_FLAG_SYNC_EP_STARTED, &subs->flags);
return err;
@ -850,7 +850,7 @@ static int snd_usb_pcm_prepare(struct snd_pcm_substream *substream)
/* for playback, submit the URBs now; otherwise, the first hwptr_done
* updates for all URBs would happen at the same time when starting */
if (subs->direction == SNDRV_PCM_STREAM_PLAYBACK)
ret = start_endpoints(subs, true);
ret = start_endpoints(subs);
unlock:
snd_usb_unlock_shutdown(subs->stream->chip);
@ -1666,7 +1666,7 @@ static int snd_usb_substream_capture_trigger(struct snd_pcm_substream *substream
switch (cmd) {
case SNDRV_PCM_TRIGGER_START:
err = start_endpoints(subs, false);
err = start_endpoints(subs);
if (err < 0)
return err;