Re: [PATCH] thermal: add thermal_zone_remove_device_groups()

[Zhang Rui <rui.zhang@intel.com>]

On Wed, 2017-01-04 at 12:35 +0800, Zhang Rui wrote:
> On Thu, 2016-12-15 at 16:47 -0500, Yasuaki Ishimatsu wrote:
> > 
> > When offlining all cores on a CPU, the following system panic
> > occurs:
> > 
> > BUG: unable to handle kernel NULL pointer dereference at (null)
> > IP: strlen+0x0/0x20
> > <snip>
> > Call Trace:
> >   ? kernfs_name_hash+0x17/0x80
> >   kernfs_find_ns+0x3f/0xd0
> >   kernfs_remove_by_name_ns+0x36/0xa0
> >   remove_files.isra.1+0x36/0x70
> >   sysfs_remove_group+0x44/0x90
> >   sysfs_remove_groups+0x2e/0x50
> >   device_remove_attrs+0x5e/0x90
> >   device_del+0x1ea/0x350
> >   device_unregister+0x1a/0x60
> >   thermal_zone_device_unregister+0x1f2/0x210
> >   pkg_thermal_cpu_offline+0x14f/0x1a0 [x86_pkg_temp_thermal]
> >   ? kzalloc.constprop.2+0x10/0x10 [x86_pkg_temp_thermal]
> >   cpuhp_invoke_callback+0x8d/0x3f0
> >   cpuhp_down_callbacks+0x42/0x80
> >   cpuhp_thread_fun+0x8b/0xf0
> >   smpboot_thread_fn+0x110/0x160
> >   kthread+0x101/0x140
> >   ? sort_range+0x30/0x30
> >   ? kthread_park+0x90/0x90
> >   ret_from_fork+0x25/0x30
> > 
> > thermal_zone_create_device_group() sets attribute_groups in
> > thermal_zone_attribute_groups[] to tz->device.groups. But these
> > attributes_groups do not have name argument.
> > 
> I'm a little confused here, in remove_files(),
> it is the (struct attribute *)->name which is passed into
> kernfs_remove_by_name, instead of attributes_groups->name.
> 
> IMO, a NULL-name attribute group won't bring any problem.
> 
hah, I see what the problem is here.
Just like the problem illustrated in this one
https://patchwork.kernel.org/patch/9492439/
The root cause is that, the trip point attributes are cleared and freed
BEFORE device_unregister(), this results in NULL trip point attributes
when removing the thermal zone device sysfs groups.

And I believe https://patchwork.kernel.org/patch/9492439/ should fix
the problem for you, right?

thanks,
rui> > 
> > So when offlining all cores on CPU and executing
> > thermal_zone_device_unregister(), the panic occurs in strlen()
> > called from kernfs_name_hash() because name argument is NULL.
> > 
> > The patch adds thermal_zone_remove_device_groups() to free
> > tz->device.groups and set NULL pointer.
> > 
> > Signed-off-by: Yasuaki Ishimatsu <isimatu.yasuaki@jp.fujitsu.com>
> > CC: Zhang Rui <rui.zhang@intel.com>
> > CC: Eduardo Valentin <edubezval@gmail.com>
> > ---
> >   drivers/thermal/thermal_core.c  | 3 ++-
> >   drivers/thermal/thermal_core.h  | 1 +
> >   drivers/thermal/thermal_sysfs.c | 6 ++++++
> >   3 files changed, 9 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/thermal/thermal_core.c
> > b/drivers/thermal/thermal_core.c
> > index 641faab..926e385 100644
> > --- a/drivers/thermal/thermal_core.c
> > +++ b/drivers/thermal/thermal_core.c
> > @@ -1251,6 +1251,7 @@ struct thermal_zone_device *
> > 
> >   unregister:
> >   	release_idr(&thermal_tz_idr, &thermal_idr_lock, tz->id);
> > +	thermal_zone_remove_device_groups(tz);
> >   	device_unregister(&tz->device);
> >   	return ERR_PTR(result);
> >   }
> > @@ -1315,8 +1316,8 @@ void thermal_zone_device_unregister(struct
> > thermal_zone_device *tz)
> >   	release_idr(&thermal_tz_idr, &thermal_idr_lock, tz->id);
> >   	idr_destroy(&tz->idr);
> >   	mutex_destroy(&tz->lock);
> > +	thermal_zone_remove_device_groups(tz);
> >   	device_unregister(&tz->device);
> > -	kfree(tz->device.groups);
> >   }
> >   EXPORT_SYMBOL_GPL(thermal_zone_device_unregister);
> > 
> > diff --git a/drivers/thermal/thermal_core.h
> > b/drivers/thermal/thermal_core.h
> > index 2412b37..e3a60db 100644
> > --- a/drivers/thermal/thermal_core.h
> > +++ b/drivers/thermal/thermal_core.h
> > @@ -70,6 +70,7 @@ void thermal_zone_device_unbind_exception(struct
> > thermal_zone_device *,
> >   int thermal_build_list_of_policies(char *buf);
> > 
> >   /* sysfs I/F */
> > +void thermal_zone_remove_device_groups(struct thermal_zone_device
> > *tz);
> >   int thermal_zone_create_device_groups(struct thermal_zone_device
> > *,
> > int);
> >   void thermal_cooling_device_setup_sysfs(struct
> > thermal_cooling_device *);
> >   /* used only at binding time */
> > diff --git a/drivers/thermal/thermal_sysfs.c
> > b/drivers/thermal/thermal_sysfs.c
> > index a694de9..3dfd29b 100644
> > --- a/drivers/thermal/thermal_sysfs.c
> > +++ b/drivers/thermal/thermal_sysfs.c
> > @@ -605,6 +605,12 @@ static int create_trip_attrs(struct
> > thermal_zone_device *tz, int mask)
> >   	return 0;
> >   }
> > 
> > +void thermal_zone_remove_device_groups(struct thermal_zone_device
> > *tz)
> > +{
> > +	kfree(tz->device.groups);
> > +	tz->device.groups = NULL;
> > +}
> > +
> >   int thermal_zone_create_device_groups(struct thermal_zone_device
> > *tz,
> >   				      int mask)
> >   {
> --
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