Re: [PATCH] ALSA: pcm: Serialize snd_pcm_suspend_all() with open_mutex

[Takashi Iwai]

On Fri, 20 Mar 2026 18:28:35 +0100,
Cássio Gabriel wrote:
> 
> snd_pcm_suspend_all() walks all PCM substreams and uses a lockless
> runtime check to skip closed streams. It then calls snd_pcm_suspend()
> for each remaining substream and finally runs snd_pcm_sync_stop() in a
> second pass.
> 
> The runtime lifetime is still controlled by pcm->open_mutex in the
> open/release path. That means a concurrent close can clear or free
> substream->runtime after the initial check in snd_pcm_suspend_all(),
> leaving the later suspend or sync-stop path to dereference a stale or
> NULL runtime pointer.
> 
> Serialize snd_pcm_suspend_all() with pcm->open_mutex so the runtime
> pointer stays stable across both loops. This matches the existing PCM
> runtime lifetime rule already used by other core paths that access
> substream->runtime outside the stream lock.
> 
> Signed-off-by: Cássio Gabriel <cassiogabrielcontato@xxxxxxxxx>

I guess it's safe to take open_mutex from this function, but it's
still worth to mention it in the function description.
Could you update the description of snd_pcm_suspend_all(), too?


thanks,

Takashi