ALSA: opl3: circular locking in the snd_opl3_note_on() and snd_opl3_note_off()

Fix following circular locking in the opl3 driver.

=======================================================
[ INFO: possible circular locking dependency detected ]
2.6.32-rc3 #87
-------------------------------------------------------
swapper/0 is trying to acquire lock:
(&opl3->voice_lock){..-...}, at: [<cca748fe>] snd_opl3_note_off+0x1e/0xe0 [snd_opl3_synth]

but task is already holding lock:
(&opl3->sys_timer_lock){..-...}, at: [<cca75169>] snd_opl3_timer_func+0x19/0xc0 [snd_opl3_synth]

which lock already depends on the new lock.

the existing dependency chain (in reverse order) is:

-> #1 (&opl3->sys_timer_lock){..-...}:
[<c02461d5>] validate_chain+0xa25/0x1040
[<c0246aca>] __lock_acquire+0x2da/0xab0
[<c024731a>] lock_acquire+0x7a/0xa0
[<c044c300>] _spin_lock_irqsave+0x40/0x60
[<cca75046>] snd_opl3_note_on+0x686/0x790 [snd_opl3_synth]
[<cca68912>] snd_midi_process_event+0x322/0x590 [snd_seq_midi_emul]
[<cca74245>] snd_opl3_synth_event_input+0x15/0x20 [snd_opl3_synth]
[<cca4dcc0>] snd_seq_deliver_single_event+0x100/0x200 [snd_seq]
[<cca4de07>] snd_seq_deliver_event+0x47/0x1f0 [snd_seq]
[<cca4e50b>] snd_seq_dispatch_event+0x3b/0x140 [snd_seq]
[<cca5008c>] snd_seq_check_queue+0x10c/0x120 [snd_seq]
[<cca5037b>] snd_seq_enqueue_event+0x6b/0xe0 [snd_seq]
[<cca4e0fd>] snd_seq_client_enqueue_event+0xdd/0x100 [snd_seq]
[<cca4eb7a>] snd_seq_write+0xea/0x190 [snd_seq]
[<c02827b6>] vfs_write+0x96/0x160
[<c0282c9d>] sys_write+0x3d/0x70
[<c0202c45>] syscall_call+0x7/0xb

-> #0 (&opl3->voice_lock){..-...}:
[<c02467e6>] validate_chain+0x1036/0x1040
[<c0246aca>] __lock_acquire+0x2da/0xab0
[<c024731a>] lock_acquire+0x7a/0xa0
[<c044c300>] _spin_lock_irqsave+0x40/0x60
[<cca748fe>] snd_opl3_note_off+0x1e/0xe0 [snd_opl3_synth]
[<cca751f0>] snd_opl3_timer_func+0xa0/0xc0 [snd_opl3_synth]
[<c022ac46>] run_timer_softirq+0x166/0x1e0
[<c02269e8>] __do_softirq+0x78/0x110
[<c0226ac6>] do_softirq+0x46/0x50
[<c0226e26>] irq_exit+0x36/0x40
[<c0204bd2>] do_IRQ+0x42/0xb0
[<c020328e>] common_interrupt+0x2e/0x40
[<c021092f>] apm_cpu_idle+0x10f/0x290
[<c0201b11>] cpu_idle+0x21/0x40
[<c04443cd>] rest_init+0x4d/0x60
[<c055c835>] start_kernel+0x235/0x280
[<c055c066>] i386_start_kernel+0x66/0x70

other info that might help us debug this:

2 locks held by swapper/0:
#0: (&opl3->tlist){+.-...}, at: [<c022abd0>] run_timer_softirq+0xf0/0x1e0
#1: (&opl3->sys_timer_lock){..-...}, at: [<cca75169>] snd_opl3_timer_func+0x19/0xc0 [snd_opl3_synth]

stack backtrace:
Pid: 0, comm: swapper Not tainted 2.6.32-rc3 #87
Call Trace:
[<c0245188>] print_circular_bug+0xc8/0xd0
[<c02467e6>] validate_chain+0x1036/0x1040
[<c0247f14>] ? check_usage_forwards+0x54/0xd0
[<c0246aca>] __lock_acquire+0x2da/0xab0
[<c024731a>] lock_acquire+0x7a/0xa0
[<cca748fe>] ? snd_opl3_note_off+0x1e/0xe0 [snd_opl3_synth]
[<c044c300>] _spin_lock_irqsave+0x40/0x60
[<cca748fe>] ? snd_opl3_note_off+0x1e/0xe0 [snd_opl3_synth]
[<cca748fe>] snd_opl3_note_off+0x1e/0xe0 [snd_opl3_synth]
[<c044c307>] ? _spin_lock_irqsave+0x47/0x60
[<cca751f0>] snd_opl3_timer_func+0xa0/0xc0 [snd_opl3_synth]
[<c022ac46>] run_timer_softirq+0x166/0x1e0
[<c022abd0>] ? run_timer_softirq+0xf0/0x1e0
[<cca75150>] ? snd_opl3_timer_func+0x0/0xc0 [snd_opl3_synth]
[<c02269e8>] __do_softirq+0x78/0x110
[<c044c0fd>] ? _spin_unlock+0x1d/0x20
[<c025915f>] ? handle_level_irq+0xaf/0xe0
[<c0226ac6>] do_softirq+0x46/0x50
[<c0226e26>] irq_exit+0x36/0x40
[<c0204bd2>] do_IRQ+0x42/0xb0
[<c024463c>] ? trace_hardirqs_on_caller+0x12c/0x180
[<c020328e>] common_interrupt+0x2e/0x40
[<c0208d88>] ? default_idle+0x38/0x50
[<c021092f>] apm_cpu_idle+0x10f/0x290
[<c0201b11>] cpu_idle+0x21/0x40
[<c04443cd>] rest_init+0x4d/0x60
[<c055c835>] start_kernel+0x235/0x280
[<c055c210>] ? unknown_bootoption+0x0/0x210
[<c055c066>] i386_start_kernel+0x66/0x70

Signed-off-by: Krzysztof Helt <[e-mail]>
Signed-off-by: Takashi Iwai <[e-mail]>

sound/drivers/opl3/opl3_midi.c

···
 
 extern int use_internal_drums;
 
+static void snd_opl3_note_off_unsafe(void *p, int note, int vel,
+				     struct snd_midi_channel *chan);
 /*
  * The next table looks magical, but it certainly is not. Its values have
  * been calculated as table[i]=8*log(i/64)/log(2) with an obvious exception
···
 	int again = 0;
 	int i;
 
-	spin_lock_irqsave(&opl3->sys_timer_lock, flags);
+	spin_lock_irqsave(&opl3->voice_lock, flags);
 	for (i = 0; i < opl3->max_voices; i++) {
 		struct snd_opl3_voice *vp = &opl3->voices[i];
 		if (vp->state > 0 && vp->note_off_check) {
 			if (vp->note_off == jiffies)
-				snd_opl3_note_off(opl3, vp->note, 0, vp->chan);
+				snd_opl3_note_off_unsafe(opl3, vp->note, 0,
+							 vp->chan);
 			else
 				again++;
 		}
 	}
+	spin_unlock_irqrestore(&opl3->voice_lock, flags);
+
+	spin_lock_irqsave(&opl3->sys_timer_lock, flags);
 	if (again) {
 		opl3->tlist.expires = jiffies + 1;	/* invoke again */
 		add_timer(&opl3->tlist);
···
 /*
  * Release a note in response to a midi note off.
  */
-void snd_opl3_note_off(void *p, int note, int vel, struct snd_midi_channel *chan)
+static void snd_opl3_note_off_unsafe(void *p, int note, int vel,
+				     struct snd_midi_channel *chan)
 {
   	struct snd_opl3 *opl3;
 
 	int voice;
 	struct snd_opl3_voice *vp;
-
-	unsigned long flags;
 
 	opl3 = p;
 
···
 		   chan->number, chan->midi_program, note);
 #endif
 
-	spin_lock_irqsave(&opl3->voice_lock, flags);
-
 	if (opl3->synth_mode == SNDRV_OPL3_MODE_SEQ) {
 		if (chan->drum_channel && use_internal_drums) {
 			snd_opl3_drum_switch(opl3, note, vel, 0, chan);
-			spin_unlock_irqrestore(&opl3->voice_lock, flags);
 			return;
 		}
 		/* this loop will hopefully kill all extra voices, because
···
 			snd_opl3_kill_voice(opl3, voice);
 		}
 	}
+}
+
+void snd_opl3_note_off(void *p, int note, int vel,
+		       struct snd_midi_channel *chan)
+{
+	struct snd_opl3 *opl3 = p;
+	unsigned long flags;
+
+	spin_lock_irqsave(&opl3->voice_lock, flags);
+	snd_opl3_note_off_unsafe(p, note, vel, chan);
 	spin_unlock_irqrestore(&opl3->voice_lock, flags);
 }