[PATCH 3.16 058/366] ALSA: core: Assure control device to be registered at last

Ben Hutchings
2018-11-12T06:01:33Z

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);
}