Re: [PATCH] driver core: fix race between creating/querying glue dir and its cleanup

[Chandra Sekhar Lingutla <clingutla@codeaurora.org>]

Hi Ming/ Greg

Curious to know your comments on this patch.

On 04/26/2016 10:57 PM, Chandra Sekhar Lingutla wrote:
> Hi Ming,
>
> On 03/28/2016 01:57 PM, Ming Lei wrote:
>> The global mutex of 'gdp_mutex' is used to serialize creating/querying
>> glue dir and its cleanup. Turns out it isn't a perfect way because
>> part(kobj_kset_leave()) of the actual cleanup action() is done inside
>> the release handler of the glue dir kobject. That means gdp_mutex has
>> to be held before releasing the last reference count of the glue dir
>> kobject.
>>
>> This patch moves glue dir's cleanup after kobject_del() in device_del()
>> for avoiding the race.
>>
>> Cc: Yijing Wang <wangyijing@huawei.com>
>> Reported-by: Chandra Sekhar Lingutla <clingutla@codeaurora.org>
>> Signed-off-by: Ming Lei <ming.lei@canonical.com>
>> ---
>>   drivers/base/core.c | 41 +++++++++++++++++++++++++++++++----------
>>   1 file changed, 31 insertions(+), 10 deletions(-)
>>
>> diff --git a/drivers/base/core.c b/drivers/base/core.c
>> index 0a8bdad..3f2e1f8 100644
>> --- a/drivers/base/core.c
>> +++ b/drivers/base/core.c
>> @@ -836,11 +836,31 @@ static struct kobject *get_device_parent(struct device *dev,
>>       return NULL;
>>   }
>>
>> +static inline bool live_in_glue_dir(struct kobject *kobj,
>> +                    struct device *dev)
>> +{
>> +    if (!kobj || !dev->class ||
>> +        kobj->kset != &dev->class->p->glue_dirs)
>> +        return true;
>> +    return false;
>> +}
> I think we should return false if kobj->kset != &dev->class->p->glue_dirs.
> If kboj->kset points to dev->class->p->glue_dirs, then we live in glue dir.
> So logic should be:
>      if (!kobj || !dev->class ||
>          kobj->kset != &dev->class->p->glue_dirs)
>              return false;
>      return true;
>
>> +
>> +static inline struct kobject *get_glue_dir(struct device *dev)
>> +{
>> +    if (live_in_glue_dir(&dev->kobj, dev))
>> +        return dev->kobj.parent;
>> +    return NULL;
>> +}
>> +
>> +/*
>> + * make sure cleaning up dir as the last step, we need to make
>> + * sure .release handler of kobject is run with holding the
>> + * global lock
>> + */
>>   static void cleanup_glue_dir(struct device *dev, struct kobject *glue_dir)
>>   {
>>       /* see if we live in a "glue" directory */
>> -    if (!glue_dir || !dev->class ||
>> -        glue_dir->kset != &dev->class->p->glue_dirs)
>> +    if (!live_in_glue_dir(glue_dir, dev))
>>           return;
>>
>>       mutex_lock(&gdp_mutex);
>> @@ -848,11 +868,6 @@ static void cleanup_glue_dir(struct device *dev, struct kobject *glue_dir)
>>       mutex_unlock(&gdp_mutex);
>>   }
>>
>> -static void cleanup_device_parent(struct device *dev)
>> -{
>> -    cleanup_glue_dir(dev, dev->kobj.parent);
>> -}
>> -
>>   static int device_add_class_symlinks(struct device *dev)
>>   {
>>       struct device_node *of_node = dev_of_node(dev);
>> @@ -1028,6 +1043,7 @@ int device_add(struct device *dev)
>>       struct kobject *kobj;
>>       struct class_interface *class_intf;
>>       int error = -EINVAL;
>> +    struct kobject *glue_dir = NULL;
>>
>>       dev = get_device(dev);
>>       if (!dev)
>> @@ -1072,8 +1088,10 @@ int device_add(struct device *dev)
>>       /* first, register with generic layer. */
>>       /* we require the name to be set before, and pass NULL */
>>       error = kobject_add(&dev->kobj, dev->kobj.parent, NULL);
>> -    if (error)
>> +    if (error) {
>> +        glue_dir = get_glue_dir(dev);
>>           goto Error;
>> +    }
>>
>>       /* notify platform of device entry */
>>       if (platform_notify)
>> @@ -1154,9 +1172,10 @@ done:
>>       device_remove_file(dev, &dev_attr_uevent);
>>    attrError:
>>       kobject_uevent(&dev->kobj, KOBJ_REMOVE);
>> +    glue_dir = get_glue_dir(dev);
>>       kobject_del(&dev->kobj);
>>    Error:
>> -    cleanup_device_parent(dev);
>> +    cleanup_glue_dir(dev, glue_dir);
>>       put_device(parent);
>>   name_error:
>>       kfree(dev->p);
>> @@ -1232,6 +1251,7 @@ EXPORT_SYMBOL_GPL(put_device);
>>   void device_del(struct device *dev)
>>   {
>>       struct device *parent = dev->parent;
>> +    struct kobject *glue_dir = NULL;
>>       struct class_interface *class_intf;
>>
>>       /* Notify clients of device removal.  This call must come
>> @@ -1276,8 +1296,9 @@ void device_del(struct device *dev)
>>           blocking_notifier_call_chain(&dev->bus->p->bus_notifier,
>>                            BUS_NOTIFY_REMOVED_DEVICE, dev);
>>       kobject_uevent(&dev->kobj, KOBJ_REMOVE);
>> -    cleanup_device_parent(dev);
>> +    glue_dir = get_glue_dir(dev);
>>       kobject_del(&dev->kobj);
>> +    cleanup_glue_dir(dev, glue_dir);
>>       put_device(parent);
>>   }
>>   EXPORT_SYMBOL_GPL(device_del);
>>

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