[PATCH v4 1/3] ALSA: opl3: Initialize the timer before publishing a sequencer port

[Cen Zhang]

snd_opl3_seq_probe() initializes the delayed-note timer and its lock
after snd_opl3_synth_create_port() has made the native port reachable.
A direct NOTEON does not require a subscription, and a fixed-duration
instrument makes it enter snd_opl3_start_timer().

On sequencer-driver rebind, the card-owned instrument bank remains
available. An event delivered as soon as the port appears can race the
late initialization:

  Sequencer driver probe             Direct NOTEON
  ----------------------             -------------
  snd_opl3_synth_create_port()
    snd_seq_event_port_attach()
      publish port
                                     snd_opl3_synth_event_input()
                                       snd_opl3_note_on()
                                         snd_opl3_start_timer()
                                           use tlist and sys_timer_lock
  timer_setup(tlist)
  spin_lock_init(sys_timer_lock)
  sys_timer_status = 0

Initialize the timer, its lock and its status before creating the client
and attaching either port. No event can then reach partially initialized
timer state or have its newly armed timer reinitialized by the probe.

Assisted-by: LLM
Signed-off-by: Cen Zhang <zzzccc427@xxxxxxxxx>
---
 sound/drivers/opl3/opl3_seq.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/sound/drivers/opl3/opl3_seq.c b/sound/drivers/opl3/opl3_seq.c
index b77d8e8f12fb..2bacefc3201d 100644
--- a/sound/drivers/opl3/opl3_seq.c
+++ b/sound/drivers/opl3/opl3_seq.c
@@ -214,6 +214,11 @@ static int snd_opl3_seq_probe(struct snd_seq_device *dev)
 
 	spin_lock_init(&opl3->voice_lock);
 
+	/* Initialize the timer before an attached port can receive events. */
+	timer_setup(&opl3->tlist, snd_opl3_timer_func, 0);
+	spin_lock_init(&opl3->sys_timer_lock);
+	opl3->sys_timer_status = 0;
+
 	opl3->seq_client = -1;
 
 	/* allocate new client */
@@ -232,11 +237,6 @@ static int snd_opl3_seq_probe(struct snd_seq_device *dev)
 		return err;
 	}
 
-	/* setup system timer */
-	timer_setup(&opl3->tlist, snd_opl3_timer_func, 0);
-	spin_lock_init(&opl3->sys_timer_lock);
-	opl3->sys_timer_status = 0;
-
 #if IS_ENABLED(CONFIG_SND_SEQUENCER_OSS)
 	snd_opl3_init_seq_oss(opl3, name);
 #endif
-- 
2.43.0