On Mon, 15 Apr 2019 08:37:18 +0200,
Kai Vehmanen wrote:
>
> Hi Takashi,
>
> On Fri, 12 Apr 2019, Takashi Iwai wrote:
>
> > +/* Unlock and unref the given client; for OSS sequencer use only */
> > +void snd_seq_client_ioctl_unlock(int clientid)
> > +{
> > + struct snd_seq_client *client;
> > +
> > + client = snd_seq_client_use_ptr(clientid);
> > + if (WARN_ON(!client))
> > + return;
> > + mutex_unlock(&client->ioctl_mutex);
> > + snd_use_lock_free(&client->use_lock);
> > + snd_seq_client_unlock(client);
>
> is that double-unlock intentional? snd_seq_client_unlock() seems to call
> the same snd_use_lock_free for the same handle as on the previous line.
Yes, it's intentional. The trick is snd_seq_client_ioctl_lock()
doesn't call snd_seq_client_unlock(), i.e. keeps refcount up. This
is, in turn, released in snd_seq_client_ioctl_unlock().
snd_seq_client_ioctl_unlock() gets its refcount at use_ptr(), hence
this releases twice. Maybe it's worth for more comments.
thanks,
Takashi
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