ALSA: usb-audio: Fix irq/process data synchronization
Commit 16200948d83 ("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: f8114f8583bb ("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>
diff --git a/sound/usb/endpoint.c b/sound/usb/endpoint.c
index 15d1d5c..2f0ea70 100644
--- a/sound/usb/endpoint.c
+++ b/sound/usb/endpoint.c
@@ -534,6 +534,11 @@
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 @@
/**
* 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 @@
*
* 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 @@
/* 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 @@
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);
}
}