From: Jia-Ju Bai <baijiaju1990@gmail.com>
To: Takashi Iwai <tiwai@suse.de>
Cc: perex@perex.cz, tiwai@suse.com, alsa-devel@alsa-project.org,
"linux-kernel@vger.kernel.org >> linux-kernel"
<linux-kernel@vger.kernel.org>
Subject: Re: [BUG] ALSA: sb16: possible ABBA deadlock in snd_sb_csp_stop() and snd_sb_csp_load()
Date: Mon, 19 Jul 2021 10:22:40 +0800 [thread overview]
Message-ID: <a160198b-19c6-5f50-329a-3f54fd464168@gmail.com> (raw)
In-Reply-To: <s5ho8b3x3wu.wl-tiwai@suse.de>
On 2021/7/15 18:33, Takashi Iwai wrote:
> On Thu, 15 Jul 2021 12:20:36 +0200,
> Jia-Ju Bai wrote:
>> Hello,
>>
>> I find there is a possible ABBA deadlock in the SB16 driver in Linux 5.10:
>>
>> In snd_sb_csp_stop():
>> 876: spin_lock_irqsave(&p->chip->mixer_lock, flags);
>> 882: spin_lock(&p->chip->reg_lock);
>>
>> In snd_sb_csp_load():
>> 614: spin_lock_irqsave(&p->chip->reg_lock, flags);
>> 653: spin_lock(&p->chip->mixer_lock);
>>
>> When snd_sb_csp_stop() and snd_sb_csp_load() are concurrently
>> executed, the deadlock can occur.
>>
>> I check the code and find a possible case of such concurrent execution:
>>
>> #CPU1:
>> snd_sb16_playback_close
>> snd_sb16_csp_playback_close (csp->ops.csp_stop(csp))
>> snd_sb_csp_stop
>>
>> #CPU2:
>> snd_sb_csp_ioctl
>> snd_sb_csp_riff_load
>> snd_sb_csp_load_user
>> snd_sb_csp_load
>>
>> I am not quite sure whether this possible deadlock is real and how to
>> fix it if it is real.
>> Any feedback would be appreciated, thanks
> The impact must be quite low, as both functions run in different
> state (running or stopped), so those are basically exclusive.
> And, above all, there is no VM supporting this chip, hence it's only
> for the real hardware and it's about very old ISA boards that maybe
> only less than handful people in the world can run now.
>
> About the fix: just split the locks in snb_sb_csp_stop() (also
> snd_sb_csp_start()) like below should suffice.
Thanks for the feedback and explanation :)
The patch looks good to me.
>
> --- a/sound/isa/sb/sb16_csp.c
> +++ b/sound/isa/sb/sb16_csp.c
> @@ -816,6 +816,7 @@ static int snd_sb_csp_start(struct snd_sb_csp * p, int sample_width, int channel
> 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 */
> @@ -855,6 +856,7 @@ static int snd_sb_csp_start(struct snd_sb_csp * p, int sample_width, int channel
> 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);
> @@ -880,6 +882,7 @@ static int snd_sb_csp_stop(struct snd_sb_csp * p)
> 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) {
> @@ -894,6 +897,7 @@ static int snd_sb_csp_stop(struct snd_sb_csp * p)
> 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);
prev parent reply other threads:[~2021-07-19 2:22 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-07-15 10:20 [BUG] ALSA: sb16: possible ABBA deadlock in snd_sb_csp_stop() and snd_sb_csp_load() Jia-Ju Bai
2021-07-15 10:33 ` Takashi Iwai
2021-07-19 2:22 ` Jia-Ju Bai [this message]
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