linux-kernel - [PATCH] Revert "ALSA: usb-audio: Fix race at stopping the stream"

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Date:   Wed, 21 Dec 2016 11:28:28 +0100
From:   Takashi Iwai <tiwai@...e.de>
To:     Linus Torvalds <torvalds@...uxfoundation.org>
Cc:     Ioan-Adrian Ratiu <adi@...rat.com>,
        Takashi Sakamoto <o-takashi@...amocchi.jp>, clemens@...isch.de,
        alsa-devel@...a-project.org, linux-kernel@...r.kernel.org
Subject: [PATCH] Revert "ALSA: usb-audio: Fix race at stopping the stream"

This reverts commit 16200948d8353fe29a473a394d7d26790deae0e7.

The commit was intended to cover the race condition, but it introduced
yet another regression for devices with the implicit feedback, leading
to a kernel panic due to NULL-dereference in an irq context.

As the race condition that was addressed by the commit is very rare
and the regression is much worse, let's revert the commit for rc1, and
fix the issue properly in a later patch.

Fixes: 16200948d835 ("ALSA: usb-audio: Fix race at stopping the stream")
Reported-by: Ioan-Adrian Ratiu <adi@...rat.com>
Cc: <stable@...r.kernel.org>
Signed-off-by: Takashi Iwai <tiwai@...e.de>
---

Linus, could you take this manually for rc1?
I'm traveling and having a difficulty to set up a git pull request
right now.  Sorry for inconvenience.

Thanks!


Takashi

 sound/usb/endpoint.c | 12 ++++--------
 1 file changed, 4 insertions(+), 8 deletions(-)

diff --git a/sound/usb/endpoint.c b/sound/usb/endpoint.c
index a2cdf3370afe..15d1d5c63c3c 100644
--- a/sound/usb/endpoint.c
+++ b/sound/usb/endpoint.c
@@ -384,9 +384,6 @@ 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 */
@@ -537,11 +534,6 @@ 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;
 }
 
@@ -1028,6 +1020,10 @@ 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);
 	}
 }
-- 
2.11.0