[PATCH] ALSA: hda - Fix hang caused by race during suspend.

[PATCH] ALSA: hda - Fix hang caused by race during suspend.

[Dylan Reid]

There was a race condition when the system suspends while hda_power_work
is running in the work queue.  If system suspend (snd_hda_suspend)
happens after the work queue releases power_lock but before it calls
hda_call_codec_suspend,  codec_suspend runs with power_on=0, causing the
codec to power up for register reads, and hanging when it calls
cancel_delayed_work_sync from the running work queue.

The call chain from the work queue will look like this:
hda_power_work <<- power_on = 1, unlock, then power_on cleard by suspend
  hda_call_codec_suspend
    hda_set_power_state
      snd_hda_codec_read
        codec_exec_verb
          snd_hda_power_up
	    snd_hda_power_save
	      __snd_hda_power_up
	        cancel_delayed_work_sync <<-- cancelling executing wq

Fix this by waiting for the work queue to finish before starting suspend
if suspend is not happening on the work queue.

Signed-off-by: Dylan Reid <dgreid@chromium.org>
---
 sound/pci/hda/hda_codec.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/sound/pci/hda/hda_codec.c b/sound/pci/hda/hda_codec.c
index 960800b..c0ab72c 100644
--- a/sound/pci/hda/hda_codec.c
+++ b/sound/pci/hda/hda_codec.c
@@ -3612,7 +3612,7 @@ static inline void hda_exec_init_verbs(struct hda_codec *codec) {}
  * call suspend and power-down; used both from PM and power-save
  * this function returns the power state in the end
  */
-static unsigned int hda_call_codec_suspend(struct hda_codec *codec)
+static unsigned int hda_call_codec_suspend(struct hda_codec *codec, bool in_wq)
 {
 	unsigned int state;
 
@@ -3620,7 +3620,9 @@ static unsigned int hda_call_codec_suspend(struct hda_codec *codec)
 		codec->patch_ops.suspend(codec);
 	hda_cleanup_all_streams(codec);
 	state = hda_set_power_state(codec, AC_PWRST_D3);
-	cancel_delayed_work(&codec->power_work);
+	/* Cancel delayed work if we aren't currently running from it. */
+	if (!in_wq)
+		cancel_delayed_work_sync(&codec->power_work);
 	spin_lock(&codec->power_lock);
 	snd_hda_update_power_acct(codec);
 	trace_hda_power_down(codec);
@@ -4478,7 +4480,7 @@ static void hda_power_work(struct work_struct *work)
 	}
 	spin_unlock(&codec->power_lock);
 
-	state = hda_call_codec_suspend(codec);
+	state = hda_call_codec_suspend(codec, true);
 	codec->pm_down_notified = 0;
 	if (!bus->power_keep_link_on && (state & AC_PWRST_CLK_STOP_OK)) {
 		codec->pm_down_notified = 1;
@@ -5127,7 +5129,7 @@ int snd_hda_suspend(struct hda_bus *bus)
 
 	list_for_each_entry(codec, &bus->codec_list, list) {
 		if (hda_codec_is_power_on(codec))
-			hda_call_codec_suspend(codec);
+			hda_call_codec_suspend(codec, false);
 	}
 	return 0;
 }
-- 
1.7.12.146.g16d26b1

Re: [PATCH] ALSA: hda - Fix hang caused by race during suspend.

[Takashi Iwai]

At Fri, 28 Sep 2012 15:57:01 -0700,
Dylan Reid wrote:
> 
> There was a race condition when the system suspends while hda_power_work
> is running in the work queue.  If system suspend (snd_hda_suspend)
> happens after the work queue releases power_lock but before it calls
> hda_call_codec_suspend,  codec_suspend runs with power_on=0, causing the
> codec to power up for register reads, and hanging when it calls
> cancel_delayed_work_sync from the running work queue.
> 
> The call chain from the work queue will look like this:
> hda_power_work <<- power_on = 1, unlock, then power_on cleard by suspend
>   hda_call_codec_suspend
>     hda_set_power_state
>       snd_hda_codec_read
>         codec_exec_verb
>           snd_hda_power_up
> 	    snd_hda_power_save
> 	      __snd_hda_power_up
> 	        cancel_delayed_work_sync <<-- cancelling executing wq
> 
> Fix this by waiting for the work queue to finish before starting suspend
> if suspend is not happening on the work queue.
> 
> Signed-off-by: Dylan Reid <dgreid@chromium.org>

I queued it for 3.7 kernel with Cc to stable.  Thanks!


Takashi

> ---
>  sound/pci/hda/hda_codec.c | 10 ++++++----
>  1 file changed, 6 insertions(+), 4 deletions(-)
> 
> diff --git a/sound/pci/hda/hda_codec.c b/sound/pci/hda/hda_codec.c
> index 960800b..c0ab72c 100644
> --- a/sound/pci/hda/hda_codec.c
> +++ b/sound/pci/hda/hda_codec.c
> @@ -3612,7 +3612,7 @@ static inline void hda_exec_init_verbs(struct hda_codec *codec) {}
>   * call suspend and power-down; used both from PM and power-save
>   * this function returns the power state in the end
>   */
> -static unsigned int hda_call_codec_suspend(struct hda_codec *codec)
> +static unsigned int hda_call_codec_suspend(struct hda_codec *codec, bool in_wq)
>  {
>  	unsigned int state;
>  
> @@ -3620,7 +3620,9 @@ static unsigned int hda_call_codec_suspend(struct hda_codec *codec)
>  		codec->patch_ops.suspend(codec);
>  	hda_cleanup_all_streams(codec);
>  	state = hda_set_power_state(codec, AC_PWRST_D3);
> -	cancel_delayed_work(&codec->power_work);
> +	/* Cancel delayed work if we aren't currently running from it. */
> +	if (!in_wq)
> +		cancel_delayed_work_sync(&codec->power_work);
>  	spin_lock(&codec->power_lock);
>  	snd_hda_update_power_acct(codec);
>  	trace_hda_power_down(codec);
> @@ -4478,7 +4480,7 @@ static void hda_power_work(struct work_struct *work)
>  	}
>  	spin_unlock(&codec->power_lock);
>  
> -	state = hda_call_codec_suspend(codec);
> +	state = hda_call_codec_suspend(codec, true);
>  	codec->pm_down_notified = 0;
>  	if (!bus->power_keep_link_on && (state & AC_PWRST_CLK_STOP_OK)) {
>  		codec->pm_down_notified = 1;
> @@ -5127,7 +5129,7 @@ int snd_hda_suspend(struct hda_bus *bus)
>  
>  	list_for_each_entry(codec, &bus->codec_list, list) {
>  		if (hda_codec_is_power_on(codec))
> -			hda_call_codec_suspend(codec);
> +			hda_call_codec_suspend(codec, false);
>  	}
>  	return 0;
>  }
> -- 
> 1.7.12.146.g16d26b1
>