On Mon, 15 Apr 2019 10:52:01 +0200, Kai Vehmanen wrote:
Hi,
On Mon, 15 Apr 2019, Takashi Iwai wrote:
+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.
ah yes, ok thanks, just checking. :) I was misled by the asymmetric names. As you are taking the refcount with two client_use_ptr() calls in both lock and unlock, would it be more logical to have two snd_seq_client_unlock() calls in unlock?
Well I thought it might be misleading to call twice, but yeah, that's rather confusing. I'll change to two sequential unlock calls with more comments.
thanks,
Takashi