From 1d0f953086f090a022f2c0e1448300c15372db46 Mon Sep 17 00:00:00 2001 From: Ioan-Adrian Ratiu Date: Thu, 5 Jan 2017 00:37:46 +0200 Subject: 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 Signed-off-by: Takashi Iwai --- sound/usb/endpoint.c | 17 +++++++---------- 1 file changed, 7 insertions(+), 10 deletions(-) (limited to 'sound/usb/endpoint.c') diff --git a/sound/usb/endpoint.c b/sound/usb/endpoint.c index 15d1d5c63c3c..2f0ea70a998c 100644 --- a/sound/usb/endpoint.c +++ b/sound/usb/endpoint.c @@ -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); } } -- cgit v1.2.1 From 13a6c8328e6056932dc680e447d4c5e8ad9add17 Mon Sep 17 00:00:00 2001 From: Ioan-Adrian Ratiu Date: Thu, 5 Jan 2017 00:37:47 +0200 Subject: ALSA: usb-audio: test EP_FLAG_RUNNING at urb completion Testing EP_FLAG_RUNNING in snd_complete_urb() before running the completion logic allows us to save a few cpu cycles by returning early, skipping the pending urb in case the stream was stopped; the stop logic handles the urb and sets the completion callbacks to NULL. Signed-off-by: Ioan-Adrian Ratiu Signed-off-by: Takashi Iwai --- sound/usb/endpoint.c | 3 +++ 1 file changed, 3 insertions(+) (limited to 'sound/usb/endpoint.c') diff --git a/sound/usb/endpoint.c b/sound/usb/endpoint.c index 2f0ea70a998c..c90607ebe155 100644 --- a/sound/usb/endpoint.c +++ b/sound/usb/endpoint.c @@ -384,6 +384,9 @@ static void snd_complete_urb(struct urb *urb) if (unlikely(atomic_read(&ep->chip->shutdown))) goto exit_clear; + if (unlikely(!test_bit(EP_FLAG_RUNNING, &ep->flags))) + goto exit_clear; + if (usb_pipeout(ep->pipe)) { retire_outbound_urb(ep, ctx); /* can be stopped during retire callback */ -- cgit v1.2.1