Re: [PATCH] ALSA: seq: midi: Serialize output teardown with event_input

[Takashi Iwai <tiwai@suse.de>]

On Tue, 26 May 2026 17:26:08 +0200,
Zhang Cen wrote:
> @@ -125,31 +128,44 @@ static int event_process_midi(struct snd_seq_event *ev, int direct,
>  	struct seq_midisynth *msynth = private_data;
>  	unsigned char msg[10];	/* buffer for constructing midi messages */
>  	struct snd_rawmidi_substream *substream;
> +	unsigned long flags;
> +	int err = 0;
>  	int len;
>  
>  	if (snd_BUG_ON(!msynth))
>  		return -EINVAL;
> +
> +	spin_lock_irqsave(&msynth->output_lock, flags);
>  	substream = msynth->output_rfile.output;
> -	if (substream == NULL)
> +	if (substream)
> +		snd_use_lock_use(&msynth->output_use_lock);
> +	spin_unlock_irqrestore(&msynth->output_lock, flags);
> +
> +	if (!substream)
>  		return -ENODEV;

Please use scoped_guard().  You can drop flags with it, and the return
-ENODEV can be right after substream assignment.

> @@ -229,12 +249,15 @@ static int midisynth_use(void *private_data, struct snd_seq_port_subscribe *info
>  	params.avail_min = 1;
>  	params.buffer_size = output_buffer_size;
>  	params.no_active_sensing = 1;
> -	err = snd_rawmidi_output_params(msynth->output_rfile.output, &params);
> +	err = snd_rawmidi_output_params(rfile.output, &params);
>  	if (err < 0) {
> -		snd_rawmidi_kernel_release(&msynth->output_rfile);
> +		snd_rawmidi_kernel_release(&rfile);
>  		return err;
>  	}
>  	snd_midi_event_reset_decode(msynth->parser);
> +	spin_lock_irqsave(&msynth->output_lock, flags);
> +	msynth->output_rfile = rfile;
> +	spin_unlock_irqrestore(&msynth->output_lock, flags);
>  	return 0;

Ditto, use guard() or scoped_guard().

> @@ -242,11 +265,20 @@ static int midisynth_use(void *private_data, struct snd_seq_port_subscribe *info
>  static int midisynth_unuse(void *private_data, struct snd_seq_port_subscribe *info)
>  {
>  	struct seq_midisynth *msynth = private_data;
> +	struct snd_rawmidi_file rfile = {};
> +	unsigned long flags;
>  
> -	if (snd_BUG_ON(!msynth->output_rfile.output))
> +	spin_lock_irqsave(&msynth->output_lock, flags);
> +	rfile = msynth->output_rfile;
> +	msynth->output_rfile = (struct snd_rawmidi_file){};
> +	spin_unlock_irqrestore(&msynth->output_lock, flags);
> +
> +	if (snd_BUG_ON(!rfile.output))
>  		return -EINVAL;

Same here, too.


thanks,

Takashi