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

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Date:	Wed, 22 Jun 2016 10:45:38 +0800
From:	Zhang Rui <rui.zhang@...el.com>
To:	Keerthy <a0393675@...com>, Eduardo Valentin <edubezval@...il.com>
Cc:	Linux PM <linux-pm@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	"R, Vignesh" <vigneshr@...com>
Subject: Re: [PATCH 02/15] thermal: sysfs: lock tz while on access to mode
 properties

On 二, 2016-06-07 at 14:52 +0530, Keerthy wrote:
> 
> On Tuesday 07 June 2016 02:38 PM, Keerthy wrote:
> > 
> > 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.
> I confirm reverting this patch helps me boot on linux-next. This
> patch 
> can be dropped as the lower layer functions are already acquiring tz-
> >lock.
> 
> Thanks Vignesh for reporting the deadlock.
> 
the root cause of the deadlock is that some platform driver invokes
thermal_zone_device_update() in .set_mode(), after mode changed.

If we wants to lock tz->ops->set_mode(), we should cleanup all the
platform thermal drivers, and deliver a thermal_zone_device_update()
in mode_store(), at the same time.

thanks,
rui

> Regards,
> Keerthy
> 
> > 
> > 
> > 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;
> > > 
> > --
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