linux-kernel - Re: [PATCH 02/15] thermal: sysfs: lock tz while on access to mode properties

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Date:	Tue, 7 Jun 2016 14:38:24 +0530
From:	Keerthy <a0393675@...com>
To:	Eduardo Valentin <edubezval@...il.com>,
	Rui Zhang <rui.zhang@...el.com>
CC:	Linux PM <linux-pm@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 02/15] thermal: sysfs: lock tz while on access to mode
 properties

Hi Eduardo,

On Tuesday 31 May 2016 12:01 PM, Eduardo Valentin wrote:
> Serialized calls to tz.ops in user facing
> sysfs handler mode_show()  and mode_store().

This seems to be causing a deadlock at boot time during the ending 
stages of boot:

http://pastebin.ubuntu.com/17085291/

It took a while to git bisect on linux-next.

Seems like you introduced new locking at the sysfs layer which causes 
this deadlock as the underlying code again tries to acquire the same 
tz->lock.

Regards,
Keerthy

>
> Cc: Zhang Rui <rui.zhang@...el.com>
> Cc: linux-pm@...r.kernel.org
> Cc: linux-kernel@...r.kernel.org
> Signed-off-by: Eduardo Valentin <edubezval@...il.com>
> ---
>   drivers/thermal/thermal_sysfs.c | 13 ++++++++++---
>   1 file changed, 10 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/thermal/thermal_sysfs.c b/drivers/thermal/thermal_sysfs.c
> index ee983ca..1db2406 100644
> --- a/drivers/thermal/thermal_sysfs.c
> +++ b/drivers/thermal/thermal_sysfs.c
> @@ -62,7 +62,9 @@ mode_show(struct device *dev, struct device_attribute *attr, char *buf)
>   	if (!tz->ops->get_mode)
>   		return -EPERM;
>
> +	mutex_lock(&tz->lock);
>   	result = tz->ops->get_mode(tz, &mode);
> +	mutex_unlock(&tz->lock);
>   	if (result)
>   		return result;
>
> @@ -75,17 +77,22 @@ mode_store(struct device *dev, struct device_attribute *attr,
>   	   const char *buf, size_t count)
>   {
>   	struct thermal_zone_device *tz = to_thermal_zone(dev);
> +	enum thermal_device_mode mode = THERMAL_DEVICE_DISABLED;
>   	int result;
>
>   	if (!tz->ops->set_mode)
>   		return -EPERM;
>
>   	if (!strncmp(buf, "enabled", sizeof("enabled") - 1))
> -		result = tz->ops->set_mode(tz, THERMAL_DEVICE_ENABLED);
> +		mode = THERMAL_DEVICE_ENABLED;
>   	else if (!strncmp(buf, "disabled", sizeof("disabled") - 1))
> -		result = tz->ops->set_mode(tz, THERMAL_DEVICE_DISABLED);
> +		mode = THERMAL_DEVICE_DISABLED;
>   	else
> -		result = -EINVAL;
> +		return -EINVAL;
> +
> +	mutex_lock(&tz->lock);
> +	result = tz->ops->set_mode(tz, mode);
> +	mutex_unlock(&tz->lock);
>
>   	if (result)
>   		return result;
>