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From:   Ben Hutchings <ben@decadent.org.uk>
To:     linux-kernel@vger.kernel.org, stable@vger.kernel.org
CC:     akpm@linux-foundation.org, "Tzung-Bi Shih" <tzungbi@google.com>,
        "Takashi Iwai" <tiwai@suse.de>
Date:   Sun, 11 Nov 2018 19:49:05 +0000
Message-ID: <lsq.1541965745.785617361@decadent.org.uk>
Subject: [PATCH 3.16 058/366] ALSA: core: Assure control device to be
 registered at last
In-Reply-To: <lsq.1541965744.387173642@decadent.org.uk>
Sender: linux-kernel-owner@vger.kernel.org
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3.16.61-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Takashi Iwai <tiwai@suse.de>

commit dc82e52492f684dcd5ed9e4773e72dbf2203d75e upstream.

The commit 289ca025ee1d ("ALSA: Use priority list for managing device
list") changed the way to register/disconnect/free devices via a
single priority list.  This helped to make behavior consistent, but it
also changed a slight behavior change: namely, the control device is
registered earlier than others, while it was supposed to be the very
last one.

I've put SNDRV_DEV_CONTROL in the current position as the release of
ctl elements often conflict with the private ctl elements some PCM or
other components may create, which often leads to a double-free.
But, the order of register and disconnect should be indeed fixed as
expected in the early days: the control device gets registered at
last, and disconnected at first.

This patch changes the priority list order to move SNDRV_DEV_CONTROL
as the last guy to assure the register / disconnect order.  Meanwhile,
for keeping the messy resource release order, manually treat the
control and lowlevel devices as last freed one.

Additional note:
The lowlevel device is the device where a card driver creates at
probe.  And, we still keep the release order control -> lowlevel, as
there might  be link from a control element back to a lowlevel object.

Fixes: 289ca025ee1d ("ALSA: Use priority list for managing device list")
Reported-by: Tzung-Bi Shih <tzungbi@google.com>
Tested-by: Tzung-Bi Shih <tzungbi@google.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
 include/sound/core.h | 2 +-
 sound/core/device.c  | 9 +++++++++
 2 files changed, 10 insertions(+), 1 deletion(-)

--- a/include/sound/core.h
+++ b/include/sound/core.h
@@ -51,7 +51,6 @@ struct completion;
  */
 enum snd_device_type {
 	SNDRV_DEV_LOWLEVEL,
-	SNDRV_DEV_CONTROL,
 	SNDRV_DEV_INFO,
 	SNDRV_DEV_BUS,
 	SNDRV_DEV_CODEC,
@@ -62,6 +61,7 @@ enum snd_device_type {
 	SNDRV_DEV_SEQUENCER,
 	SNDRV_DEV_HWDEP,
 	SNDRV_DEV_JACK,
+	SNDRV_DEV_CONTROL,	/* NOTE: this must be the last one */
 };
 
 enum snd_device_state {
--- a/sound/core/device.c
+++ b/sound/core/device.c
@@ -219,6 +219,15 @@ void snd_device_free_all(struct snd_card
 
 	if (snd_BUG_ON(!card))
 		return;
+	list_for_each_entry_safe_reverse(dev, next, &card->devices, list) {
+		/* exception: free ctl and lowlevel stuff later */
+		if (dev->type == SNDRV_DEV_CONTROL ||
+		    dev->type == SNDRV_DEV_LOWLEVEL)
+			continue;
+		__snd_device_free(dev);
+	}
+
+	/* free all */
 	list_for_each_entry_safe_reverse(dev, next, &card->devices, list)
 		__snd_device_free(dev);
 }