[PATCH 4.4 32/47] ALSA: sb: Fix potential ABBA deadlock in CSP driver

[Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>]

From: Takashi Iwai <tiwai@xxxxxxx>

commit 1c2b9519159b470ef24b2638f4794e86e2952ab7 upstream.

SB16 CSP driver may hit potentially a typical ABBA deadlock in two
code paths:

 In snd_sb_csp_stop():
     spin_lock_irqsave(&p->chip->mixer_lock, flags);
     spin_lock(&p->chip->reg_lock);

 In snd_sb_csp_load():
     spin_lock_irqsave(&p->chip->reg_lock, flags);
     spin_lock(&p->chip->mixer_lock);

Also the similar pattern is seen in snd_sb_csp_start().

Although the practical impact is very small (those states aren't
triggered in the same running state and this happens only on a real
hardware, decades old ISA sound boards -- which must be very difficult
to find nowadays), it's a real scenario and has to be fixed.

This patch addresses those deadlocks by splitting the locks in
snd_sb_csp_start() and snd_sb_csp_stop() for avoiding the nested
locks.

Reported-by: Jia-Ju Bai <baijiaju1990@xxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Link: https://lore.kernel.org/r/7b0fcdaf-cd4f-4728-2eae-48c151a92e10@xxxxxxxxx
Link: https://lore.kernel.org/r/20210716132723.13216-1-tiwai@xxxxxxx
Signed-off-by: Takashi Iwai <tiwai@xxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 sound/isa/sb/sb16_csp.c |    4 ++++
 1 file changed, 4 insertions(+)

--- a/sound/isa/sb/sb16_csp.c
+++ b/sound/isa/sb/sb16_csp.c
@@ -828,6 +828,7 @@ static int snd_sb_csp_start(struct snd_s
 	mixR = snd_sbmixer_read(p->chip, SB_DSP4_PCM_DEV + 1);
 	snd_sbmixer_write(p->chip, SB_DSP4_PCM_DEV, mixL & 0x7);
 	snd_sbmixer_write(p->chip, SB_DSP4_PCM_DEV + 1, mixR & 0x7);
+	spin_unlock_irqrestore(&p->chip->mixer_lock, flags);
 
 	spin_lock(&p->chip->reg_lock);
 	set_mode_register(p->chip, 0xc0);	/* c0 = STOP */
@@ -867,6 +868,7 @@ static int snd_sb_csp_start(struct snd_s
 	spin_unlock(&p->chip->reg_lock);
 
 	/* restore PCM volume */
+	spin_lock_irqsave(&p->chip->mixer_lock, flags);
 	snd_sbmixer_write(p->chip, SB_DSP4_PCM_DEV, mixL);
 	snd_sbmixer_write(p->chip, SB_DSP4_PCM_DEV + 1, mixR);
 	spin_unlock_irqrestore(&p->chip->mixer_lock, flags);
@@ -892,6 +894,7 @@ static int snd_sb_csp_stop(struct snd_sb
 	mixR = snd_sbmixer_read(p->chip, SB_DSP4_PCM_DEV + 1);
 	snd_sbmixer_write(p->chip, SB_DSP4_PCM_DEV, mixL & 0x7);
 	snd_sbmixer_write(p->chip, SB_DSP4_PCM_DEV + 1, mixR & 0x7);
+	spin_unlock_irqrestore(&p->chip->mixer_lock, flags);
 
 	spin_lock(&p->chip->reg_lock);
 	if (p->running & SNDRV_SB_CSP_ST_QSOUND) {
@@ -906,6 +909,7 @@ static int snd_sb_csp_stop(struct snd_sb
 	spin_unlock(&p->chip->reg_lock);
 
 	/* restore PCM volume */
+	spin_lock_irqsave(&p->chip->mixer_lock, flags);
 	snd_sbmixer_write(p->chip, SB_DSP4_PCM_DEV, mixL);
 	snd_sbmixer_write(p->chip, SB_DSP4_PCM_DEV + 1, mixR);
 	spin_unlock_irqrestore(&p->chip->mixer_lock, flags);