Re: [bug report] ALSA: seq: Use no intrruptible mutex_lock

[Takashi Iwai <tiwai@xxxxxxx>]

On Mon, 01 Feb 2021 14:13:14 +0100,
Dan Carpenter wrote:
> 
> Hello Takashi Iwai,
> 
> The patch 04702e8d0092: "ALSA: seq: Use no intrruptible mutex_lock"
> from Aug 1, 2018, leads to the following static checker warning:
> 
> 	sound/core/seq/seq_clientmgr.c:2194 snd_seq_create_kernel_client()
> 	warn: called with lock held.  '&register_mutex'
> 
> sound/core/seq/seq_midi.c
>    294          if (ports > (256 / SNDRV_RAWMIDI_DEVICES))
>    295                  ports = 256 / SNDRV_RAWMIDI_DEVICES;
>    296  
>    297          mutex_lock(&register_mutex);
>                            ^^^^^^^^^^^^^^^
> Holding lock
> 
>    298          client = synths[card->number];
>    299          if (client == NULL) {
>    300                  newclient = 1;
>    301                  client = kzalloc(sizeof(*client), GFP_KERNEL);
>    302                  if (client == NULL) {
>    303                          mutex_unlock(&register_mutex);
>    304                          kfree(info);
>    305                          return -ENOMEM;
>    306                  }
>    307                  client->seq_client =
>    308                          snd_seq_create_kernel_client(
>                                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> Deadlock
> 
>    309                                  card, 0, "%s", card->shortname[0] ?
>    310                                  (const char *)card->shortname : "External MIDI");
>    311                  if (client->seq_client < 0) {
>    312                          kfree(client);
>    313                          mutex_unlock(&register_mutex);
>    314                          kfree(info);
>    315                          return -ENOMEM;
>    316                  }
>    317          }

Again, both register_mutex are different instances, where both are
local static variables, hence they can't conflict with each other.


thanks,

Takashi