[alsa-devel] [PATCH 1/6] ALSA: seq-dummy: remove deadlock-causing events on close

[Takashi Iwai]

At Sun, 25 Jan 2015 14:34:29 +0100,
Clemens Ladisch wrote:
> 
> When the last subscriber to a "Through" port has been removed, the
> subscribed destination ports might still be active, so it would be
> wrong to send "all sounds off" and "reset controller" events to them.
> The proper place for such a shutdown would be the closing of the actual
> MIDI port (and close_substream() in rawmidi.c already can do this).
> 
> This also fixes a deadlock when dummy_unuse() tries to send events to
> its own port that is already locked because it is being freed.
> 
> Reported-by: Peter Billam <peter at www.pjb.com.au>
> Fixes: 1da177e4c3f4
> Cc: <stable at vger.kernel.org>
> Signed-off-by: Clemens Ladisch <clemens at ladisch.de>

Applied to for-linus branch, but I dropped the fixes tag that points
to 2.6.12-rc2, which is obviously not so useful.


thanks,

Takashi

> ---
>  sound/core/seq/seq_dummy.c |   31 -------------------------------
>  1 file changed, 31 deletions(-)
> 
> diff --git a/sound/core/seq/seq_dummy.c b/sound/core/seq/seq_dummy.c
> index ec667f1..5d905d9 100644
> --- a/sound/core/seq/seq_dummy.c
> +++ b/sound/core/seq/seq_dummy.c
> @@ -82,36 +82,6 @@ struct snd_seq_dummy_port {
>  static int my_client = -1;
> 
>  /*
> - * unuse callback - send ALL_SOUNDS_OFF and RESET_CONTROLLERS events
> - * to subscribers.
> - * Note: this callback is called only after all subscribers are removed.
> - */
> -static int
> -dummy_unuse(void *private_data, struct snd_seq_port_subscribe *info)
> -{
> -	struct snd_seq_dummy_port *p;
> -	int i;
> -	struct snd_seq_event ev;
> -
> -	p = private_data;
> -	memset(&ev, 0, sizeof(ev));
> -	if (p->duplex)
> -		ev.source.port = p->connect;
> -	else
> -		ev.source.port = p->port;
> -	ev.dest.client = SNDRV_SEQ_ADDRESS_SUBSCRIBERS;
> -	ev.type = SNDRV_SEQ_EVENT_CONTROLLER;
> -	for (i = 0; i < 16; i++) {
> -		ev.data.control.channel = i;
> -		ev.data.control.param = MIDI_CTL_ALL_SOUNDS_OFF;
> -		snd_seq_kernel_client_dispatch(p->client, &ev, 0, 0);
> -		ev.data.control.param = MIDI_CTL_RESET_CONTROLLERS;
> -		snd_seq_kernel_client_dispatch(p->client, &ev, 0, 0);
> -	}
> -	return 0;
> -}
> -
> -/*
>   * event input callback - just redirect events to subscribers
>   */
>  static int
> @@ -175,7 +145,6 @@ create_port(int idx, int type)
>  		| SNDRV_SEQ_PORT_TYPE_PORT;
>  	memset(&pcb, 0, sizeof(pcb));
>  	pcb.owner = THIS_MODULE;
> -	pcb.unuse = dummy_unuse;
>  	pcb.event_input = dummy_input;
>  	pcb.private_free = dummy_free;
>  	pcb.private_data = rec;
>