On Wed, 16 May 2018 07:29:44 +0200,
Takashi Iwai wrote:
>
> On Wed, 16 May 2018 00:22:40 +0200,
> Tzung-Bi Shih wrote:
> >
> > We noticed the issue because in some rarely case the code will be executed
> > by worker of workqueue (i.e. deferral probe since v3.4) instead of udevd.
> > As a result, applications rely on the change uevent of sound card (fired
> > from 78-sound-card.rules) will be signaled prematurely. The applications
> > assume when they receive the signal, everything of the sound card should be
> > ready. But in the case, they are still initializing.
> >
> > We have tried to change the order of SNDRV_DEV_CONTROL to the last one to
> > fix the bug we met and it was doing great. So if there will not bring any
> > side effect, it should be fine to apply the patch.
>
> The register and disconnect should be OK, as they are merely the parts
> to expose to and hide from user-space.
>
> > By the way, out of curiosity, prior to the commit 289ca025ee1d, it seems
> > the list is merely a FIFO. How to ensure control device is the last one to
> > register at that time?
>
> It's just the fact that snd_ctl_new() is called inside the
> snd_card_new(), i.e. it's the very first one to be added.
On the second thought, calling the free for control at the very last
isn't always good. A ctl element might have a reference to a card
"chip" object that was allocated as lowlevel device object, and often
it refers in the private_free call, too. So, at best, we should
release the control before the lowlevel.
A revised patch is below. Give it a try.
thanks,
Takashi
-- 8< --
From: Takashi Iwai <tiwai@xxxxxxx>
Subject: [PATCH] ALSA: core: Assure control device to be registered at last
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@xxxxxxxxxx>
Signed-off-by: Takashi Iwai <tiwai@xxxxxxx>
---
include/sound/core.h | 2 +-
sound/core/device.c | 9 +++++++++
2 files changed, 10 insertions(+), 1 deletion(-)
diff --git a/include/sound/core.h b/include/sound/core.h
index 5f181b875c2f..36a5934cf4b1 100644
--- 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 {
diff --git a/sound/core/device.c b/sound/core/device.c
index cb0e46f66cc9..535102d564e3 100644
--- a/sound/core/device.c
+++ b/sound/core/device.c
@@ -240,6 +240,15 @@ void snd_device_free_all(struct snd_card *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);
}
--
2.16.3
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