Re: [PATCH] ALSA: info: Fix potential deadlock at disconnection

[Takashi Iwai <tiwai@xxxxxxx>]

On Thu, 09 Nov 2023 16:04:21 +0100,
Jaroslav Kysela wrote:
> 
> On 09. 11. 23 15:19, Takashi Iwai wrote:
> > As reported recently, ALSA core info helper may cause a deadlock at
> > the forced device disconnection during the procfs operation.
> > 
> > The proc_remove() (that is called from the snd_card_disconnect()
> > helper) has a synchronization of the pending procfs accesses via
> > wait_for_completion().  Meanwhile, ALSA procfs helper takes the global
> > mutex_lock(&info_mutex) at both the proc_open callback and
> > snd_card_info_disconnect() helper.  Since the proc_open can't finish
> > due to the mutex lock, wait_for_completion() never returns, either,
> > hence it deadlocks.
> 
> Really nice fix. Thanks Takashi.
> 
> Reviewed-by: Jaroslav Kysela <perex@xxxxxxxx>
> 
> (maybe Cc: to stable?)

Yes, I'll add it.


thanks,

Takashi