Re: [PATCH] ALSA: dummy: Refresh the CD capture switch before use

[Cen Zhang]

Hi Takashi,

Takashi Iwai <tiwai@xxxxxxx> 于2026年10月16日周五 19:49写道：
>
> On Fri, 16 Oct 2026 04:01:10 +0200,
> Cen Zhang wrote:
> >
> > The CD Capture Switch control must remain live while
> > snd_dummy_iobox_put() updates its access flags and uses its ID for
> > notification. snd_card_dummy_new_mixer() caches the control pointer, but
> > snd_ctl_remove_id() can unlink and free it without updating that cache.
> >
> > This requires a kernel caller to remove the switch while the dummy card
> > stays connected and External I/O Box remains writable. Userspace
> > ELEM_REMOVE rejects this driver control because it lacks
> > SNDRV_CTL_ELEM_ACCESS_USER.
>
> So, the removal shouldn't happen, but...
>
> > With I/O Box initially 1 and CD Volume still
> > present, the following ordered sequence is possible:
> >
> >   1. snd_ctl_remove_id() takes controls_rwsem for write, finds and
> >      unlinks CD Capture Switch, sends removal notifications and calls
> >      snd_ctl_free_one(), then drops the semaphore and returns.
>
> ... how this happens at all?  Unless 1 really happens, the rest are
> fictional dreams.
>
> The same for another dummy driver patch.  Does it really happen at
> all?
>
>
> thanks,
>
> Takashi

Thanks very much for the review. You're right. It is AI obfuscation.
After carefully checking the code myself, I could not find a real path
that removes them.

I'm very, very sorry for this noise. Please disregard both patches.
I'll be much more careful in the future.

Best regards,
Cen Zhang