Patch "ALSA: line6: Give up on the lock while URBs are released." has been added to the 4.7-stable tree

This is a note to let you know that I've just added the patch titled

ALSA: line6: Give up on the lock while URBs are released.

to the 4.7-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
alsa-line6-give-up-on-the-lock-while-urbs-are-released.patch
and it can be found in the queue-4.7 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Andrej Krutak <[email protected]>
Date: Thu, 18 Aug 2016 23:52:11 +0200
Subject: ALSA: line6: Give up on the lock while URBs are released.

From: Andrej Krutak <[email protected]>

commit adc8a43a6d6688272ebffa81789fa857e603dec6 upstream.

Done, because line6_stream_stop() locks and calls line6_unlink_audio_urbs(), which in turn invokes audio_out_callback(), which tries to lock 2nd time.

Fixes:

=============================================
[ INFO: possible recursive locking detected ]
4.4.15+ #15 Not tainted
---------------------------------------------
mplayer/3591 is trying to acquire lock:
(&(&line6pcm->out.lock)->rlock){-.-...}, at: [<bfa27655>] audio_out_callback+0x70/0x110 [snd_usb_line6]

but task is already holding lock:
(&(&line6pcm->out.lock)->rlock){-.-...}, at: [<bfa26aad>] line6_stream_stop+0x24/0x5c [snd_usb_line6]

other info that might help us debug this:

 Possible unsafe locking scenario:

       CPU0
       ----

lock(&(&line6pcm->out.lock)->rlock);
lock(&(&line6pcm->out.lock)->rlock);

*** DEADLOCK ***

May be due to missing lock nesting notation

3 locks held by mplayer/3591:

 #0:  (snd_pcm_link_rwlock){.-.-..}, at: [<bf8d49a7>] snd_pcm_stream_lock+0x1e/0x40 [snd_pcm]
 #1:  (&(&substream->self_group.lock)->rlock){-.-...}, at: [<bf8d49af>] snd_pcm_stream_lock+0x26/0x40 [snd_pcm]
 #2:  (&(&line6pcm->out.lock)->rlock){-.-...}, at: [<bfa26aad>] line6_stream_stop+0x24/0x5c [snd_usb_line6]

stack backtrace:
CPU: 0 PID: 3591 Comm: mplayer Not tainted 4.4.15+ #15
Hardware name: Generic AM33XX (Flattened Device Tree)
[<c0015d85>] (unwind_backtrace) from [<c001253d>] (show_stack+0x11/0x14)
[<c001253d>] (show_stack) from [<c02f1bdf>] (dump_stack+0x8b/0xac)
[<c02f1bdf>] (dump_stack) from [<c0076f43>] (__lock_acquire+0xc8b/0x1780)
[<c0076f43>] (__lock_acquire) from [<c007810d>] (lock_acquire+0x99/0x1c0)
[<c007810d>] (lock_acquire) from [<c06171e7>] (_raw_spin_lock_irqsave+0x3f/0x4c)
[<c06171e7>] (_raw_spin_lock_irqsave) from [<bfa27655>] (audio_out_callback+0x70/0x110 [snd_usb_line6])
[<bfa27655>] (audio_out_callback [snd_usb_line6]) from [<c04294db>] (__usb_hcd_giveback_urb+0x53/0xd0)
[<c04294db>] (__usb_hcd_giveback_urb) from [<c046388d>] (musb_giveback+0x3d/0x98)
[<c046388d>] (musb_giveback) from [<c04647f5>] (musb_urb_dequeue+0x6d/0x114)
[<c04647f5>] (musb_urb_dequeue) from [<c042ac11>] (usb_hcd_unlink_urb+0x39/0x98)
[<c042ac11>] (usb_hcd_unlink_urb) from [<bfa26a87>] (line6_unlink_audio_urbs+0x6a/0x6c [snd_usb_line6])
[<bfa26a87>] (line6_unlink_audio_urbs [snd_usb_line6]) from [<bfa26acb>] (line6_stream_stop+0x42/0x5c [snd_usb_line6])
[<bfa26acb>] (line6_stream_stop [snd_usb_line6]) from [<bfa26fe7>] (snd_line6_trigger+0xb6/0xf4 [snd_usb_line6])
[<bfa26fe7>] (snd_line6_trigger [snd_usb_line6]) from [<bf8d47b7>] (snd_pcm_do_stop+0x36/0x38 [snd_pcm])
[<bf8d47b7>] (snd_pcm_do_stop [snd_pcm]) from [<bf8d462f>] (snd_pcm_action_single+0x22/0x40 [snd_pcm])
[<bf8d462f>] (snd_pcm_action_single [snd_pcm]) from [<bf8d46f9>] (snd_pcm_action+0xac/0xb0 [snd_pcm])
[<bf8d46f9>] (snd_pcm_action [snd_pcm]) from [<bf8d4b61>] (snd_pcm_drop+0x38/0x64 [snd_pcm])
[<bf8d4b61>] (snd_pcm_drop [snd_pcm]) from [<bf8d6233>] (snd_pcm_common_ioctl1+0x7fe/0xbe8 [snd_pcm])
[<bf8d6233>] (snd_pcm_common_ioctl1 [snd_pcm]) from [<bf8d6779>] (snd_pcm_playback_ioctl1+0x15c/0x51c [snd_pcm])
[<bf8d6779>] (snd_pcm_playback_ioctl1 [snd_pcm]) from [<bf8d6b59>] (snd_pcm_playback_ioctl+0x20/0x28 [snd_pcm])
[<bf8d6b59>] (snd_pcm_playback_ioctl [snd_pcm]) from [<c016714b>] (do_vfs_ioctl+0x3af/0x5c8)

---
 sound/usb/line6/pcm.c |    2 ++
 1 file changed, 2 insertions(+)

@@ -210,7 +210,9 @@ static void line6_stream_stop(struct snd
 	spin_lock_irqsave(&pstr->lock, flags);
 	clear_bit(type, &pstr->running);
 	if (!pstr->running) {
+		spin_unlock_irqrestore(&pstr->lock, flags);
 		line6_unlink_audio_urbs(line6pcm, pstr);
+		spin_lock_irqsave(&pstr->lock, flags);
 		if (direction == SNDRV_PCM_STREAM_CAPTURE) {
 			line6pcm->prev_fbuf = NULL;
 			line6pcm->prev_fsize = 0;

Patches currently in stable-queue which might be from [email protected] are

queue-4.7/alsa-line6-give-up-on-the-lock-while-urbs-are-released.patch queue-4.7/alsa-line6-remove-double-line6_pcm_release-after-failed-acquire.patch queue-4.7/alsa-line6-fix-pod-sysfs-attributes-segfault.patch