On Mon, 25 Mar 2019 16:31:26 +0100, Jon Hunter wrote:
On 25/03/2019 09:59, Takashi Iwai wrote:
...
I reconsidered the problem again, and noticed that the very same problem may appear with the system PM, not only with runtime PM. The suspend can happen at any time, so even a stream in OPEN state may go to suspend, and you'll hit the same problem. It's just a corner case so no one really cared much.
So, I think the patch like below should fix the problem. This can be easily backported to all stable trees, and it alone should work without backporting the else intrusive changes.
Could you check whether my theory is correct?
thanks,
Takashi
From: Takashi Iwai tiwai@suse.de Subject: [PATCH] ALSA: pcm: Don't suspend stream in unrecoverable PCM state
Currently PCM core sets each opened stream forcibly to SUSPENDED state via snd_pcm_suspend_all() call, and the user-space is responsible for re-triggering the resume manually either via snd_pcm_resume() or prepare call. The scheme works fine usually, but there are corner cases where the stream can't be resumed by that call: the streams still in OPEN state before finishing hw_params. When they are suspended, user-space cannot perform resume or prepare because they haven't been set up yet. The only possible recovery is to re-open the device, which isn't nice at all. Similarly, when a stream is in DISCONNECTED state, it makes no sense to change it to SUSPENDED state. Ditto for in SETUP state; which you can re-prepare directly.
So, this patch addresses these issues by filtering the PCM streams to be suspended by checking the PCM state. When a stream is in either OPEN, SETUP or DISCONNECTED as well as already SUSPENDED, the suspend action is skipped.
To be noted, this problem was originally reported for the PCM runtime PM on HD-audio. And, the runtime PM problem itself was already addressed (although not intended) by the code refactoring commits 3d21ef0b49f8 ("ALSA: pcm: Suspend streams globally via device type PM ops") and 17bc4815de58 ("ALSA: pci: Remove superfluous snd_pcm_suspend*() calls"). These commits eliminated the snd_pcm_suspend*() calls from the runtime PM suspend callback code path, hence the racy OPEN state won't appear while runtime PM. (FWIW, the race window is between snd_pcm_open_substream() and the first power up in azx_pcm_open().)
Although the runtime PM issue was already "fixed", the same problem is still present for the system PM, hence this patch is still needed. And for stable trees, this patch alone should suffice for fixing the runtime PM problem, too.
Reported-by: Jonathan Hunter jonathanh@nvidia.com Cc: stable@vger.kernel.org Signed-off-by: Takashi Iwai tiwai@suse.de
sound/core/pcm_native.c | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-)
diff --git a/sound/core/pcm_native.c b/sound/core/pcm_native.c index f731f904e8cc..1d8452912b14 100644 --- a/sound/core/pcm_native.c +++ b/sound/core/pcm_native.c @@ -1445,8 +1445,15 @@ static int snd_pcm_pause(struct snd_pcm_substream *substream, int push) static int snd_pcm_pre_suspend(struct snd_pcm_substream *substream, int state) { struct snd_pcm_runtime *runtime = substream->runtime;
- if (runtime->status->state == SNDRV_PCM_STATE_SUSPENDED)
- switch (runtime->status->state) {
- case SNDRV_PCM_STATE_SUSPENDED: return -EBUSY;
- /* unresumable PCM state; return -EBUSY for skipping suspend */
- case SNDRV_PCM_STATE_OPEN:
- case SNDRV_PCM_STATE_SETUP:
- case SNDRV_PCM_STATE_DISCONNECTED:
return -EBUSY;- } runtime->trigger_master = substream; return 0;
}
Thanks, this works for me! I have tested this on stable branch linux-5.0.y with Tegra194. So feel free to add my ...
Tested-by: Jon Hunter jonathanh@nvidia.com
OK, I'm going to queue the fix now. Thanks for quick testing!
Takashi