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@suse.de 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@google.com Signed-off-by: Takashi Iwai tiwai@suse.de --- 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); }