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Subject[PATCH 5.4 074/108] ALSA: sb: Fix potential ABBA deadlock in CSP driver
Date
From: Takashi Iwai <tiwai@suse.de>

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@gmail.com>
Cc: <stable@vger.kernel.org>
Link: https://lore.kernel.org/r/7b0fcdaf-cd4f-4728-2eae-48c151a92e10@gmail.com
Link: https://lore.kernel.org/r/20210716132723.13216-1-tiwai@suse.de
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
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
@@ -814,6 +814,7 @@ 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 */
@@ -853,6 +854,7 @@ 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);
@@ -878,6 +880,7 @@ 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) {
@@ -892,6 +895,7 @@ 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);

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