Patch "ALSA: pcm: Fix lockdep warning with nonatomic PCM ops" has been added to the 4.1-stable tree

[<gregkh@linuxfoundation.org>]

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

    ALSA: pcm: Fix lockdep warning with nonatomic PCM ops

to the 4.1-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-pcm-fix-lockdep-warning-with-nonatomic-pcm-ops.patch
and it can be found in the queue-4.1 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From 67756e3191c90e7c0b94b8b2fb63de255b6cd337 Mon Sep 17 00:00:00 2001
From: Takashi Iwai <tiwai@suse.de>
Date: Fri, 17 Jul 2015 15:22:33 +0200
Subject: ALSA: pcm: Fix lockdep warning with nonatomic PCM ops

From: Takashi Iwai <tiwai@suse.de>

commit 67756e3191c90e7c0b94b8b2fb63de255b6cd337 upstream.

With the nonatomic PCM ops, the system may spew lockdep warnings like:

 =============================================
 [ INFO: possible recursive locking detected ]
 4.2.0-rc1-jeejaval3 #12 Not tainted
 ---------------------------------------------
 aplay/4029 is trying to acquire lock:
  (snd_pcm_link_rwsem){.+.+.+}, at: [<ffffffff816fd473>] snd_pcm_stream_lock+0x43/0x60

 but task is already holding lock:
  (snd_pcm_link_rwsem){.+.+.+}, at: [<ffffffff816fcf29>] snd_pcm_action_nonatomic+0x29/0x80

 other info that might help us debug this:
  Possible unsafe locking scenario:

        CPU0
        ----
   lock(snd_pcm_link_rwsem);
   lock(snd_pcm_link_rwsem);

Although this is false-positive as the rwsem is taken always as
read-only for these code paths, it's certainly annoying to see this at
any occasion.  A simple fix is to use down_read_nested() in
snd_pcm_stream_lock() that can be called inside another lock.

Reported-by: Vinod Koul <vinod.koul@intel.com>
Reported-by: Jeeja Kp <jeeja.kp@intel.com>
Tested-by: Jeeja Kp <jeeja.kp@intel.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 sound/core/pcm_native.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/sound/core/pcm_native.c
+++ b/sound/core/pcm_native.c
@@ -85,7 +85,7 @@ static DECLARE_RWSEM(snd_pcm_link_rwsem)
 void snd_pcm_stream_lock(struct snd_pcm_substream *substream)
 {
 	if (substream->pcm->nonatomic) {
-		down_read(&snd_pcm_link_rwsem);
+		down_read_nested(&snd_pcm_link_rwsem, SINGLE_DEPTH_NESTING);
 		mutex_lock(&substream->self_group.mutex);
 	} else {
 		read_lock(&snd_pcm_link_rwlock);


Patches currently in stable-queue which might be from tiwai@suse.de are

queue-4.1/alsa-line6-fix-ebusy-error-during-active-monitoring.patch
queue-4.1/alsa-hda-add-new-amd-pci-ids-with-proper-driver-caps.patch
queue-4.1/alsa-usb-audio-add-midi-support-for-steinberg-mi2-mi4.patch
queue-4.1/alsa-hda-apply-fixup-for-another-toshiba-satellite-s50d.patch
queue-4.1/alsa-pcm-fix-lockdep-warning-with-nonatomic-pcm-ops.patch
queue-4.1/alsa-hda-add-new-gpu-codec-id-0x10de007d-to-snd-hda.patch
queue-4.1/alsa-usb-audio-add-db-range-mapping-for-some-devices.patch
queue-4.1/alsa-hda-add-headset-mic-support-for-acer-aspire-v5-573g.patch
queue-4.1/alsa-hda-apply-a-fixup-to-dell-vostro-5480.patch
queue-4.1/alsa-hda-fix-macbook-pro-5-2-quirk.patch
queue-4.1/alsa-hda-add-headset-mic-pin-quirk-for-a-dell-device.patch