Date:	Mon, 15 Apr 2013 13:05:06 -0500
From:	Nathan Zimmer <nzimmer@....com>
To:	Dirk Brandewie <dirk.brandewie@...il.com>
CC:	<sedat.dilek@...il.com>, "Rafael J. Wysocki" <rjw@...k.pl>,
	Viresh Kumar <viresh.kumar@...aro.org>,
	Dirk Brandewie <dirk.j.brandewie@...el.com>,
	Stephen Rothwell <sfr@...b.auug.org.au>,
	<linux-next@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<cpufreq@...r.kernel.org>,
	Linux PM list <linux-pm@...r.kernel.org>,
	Lists linaro-kernel <linaro-kernel@...ts.linaro.org>
Subject: Re: linux-next: Tree for Apr 9 [cpufreq: NULL pointer deref]

On 04/15/2013 12:42 PM, Dirk Brandewie wrote:
> On 04/15/2013 10:27 AM, Nathan Zimmer wrote:
>> On 04/15/2013 11:07 AM, Dirk Brandewie wrote:
>>> On 04/13/2013 02:55 AM, Sedat Dilek wrote:
>>>> On Sat, Apr 13, 2013 at 12:51 AM, Rafael J. Wysocki <rjw@...k.pl> 
>>>> wrote:
>>>>> On Friday, April 12, 2013 11:08:37 PM Sedat Dilek wrote:
>>>>>> On Fri, Apr 12, 2013 at 6:27 PM, Sedat Dilek 
>>>>>> <sedat.dilek@...il.com> wrote:
>>>>>>> On Fri, Apr 12, 2013 at 5:45 PM, Sedat Dilek 
>>>>>>> <sedat.dilek@...il.com> wrote:
>>>>>>>> On Fri, Apr 12, 2013 at 4:24 PM, Sedat Dilek 
>>>>>>>> <sedat.dilek@...il.com> wrote:
>>>>>>>>> On Fri, Apr 12, 2013 at 10:23 AM, Viresh Kumar 
>>>>>>>>> <viresh.kumar@...aro.org>
>>>>>>>>> wrote:
>>>>>>>>>> On 10 April 2013 11:44, Sedat Dilek <sedat.dilek@...il.com> 
>>>>>>>>>> wrote:
>>>>>>>>>>> I found this "[RFC PATCH] kbuild: Build linux-tools package 
>>>>>>>>>>> with 'make
>>>>>>>>>>> deb-pkg'" from February 2012.
>>>>>>>>>>> Can't say what happened to it...
>>>>>>>>>>
>>>>>>>>>> Sedat,
>>>>>>>>>>
>>>>>>>>>> Sorry for being late. I am down with Fever and throat 
>>>>>>>>>> infection since
>>>>>>>>>> few days.
>>>>>>>>>> Still struggling with it..
>>>>>>>>>>
>>>>>>>>>> There are few things i tried. Firstly the tag: next-20130326 
>>>>>>>>>> is bad as
>>>>>>>>>> there are
>>>>>>>>>> some bad commits in cpufreq core in it.
>>>>>>>>>>
>>>>>>>>>> I then tried latest linux-next/master on my Thinkpad (model name
>>>>>>>>>> : Intel(R)
>>>>>>>>>> Core(TM) i7-2640M CPU @ 2.80GHz) and couldn't boot it up. My 
>>>>>>>>>> ubuntu
>>>>>>>>>> just hanged.
>>>>>>>>>>
>>>>>>>>>> Then i tried Rafael's linux-next branch
>>>>>>>>>>
>>>>>>>>>> 079576f Merge branch 'pm-cpufreq-next' into linux-next
>>>>>>>>>>
>>>>>>>>>> And couldn't find any issues with it. I am easily able to 
>>>>>>>>>> remove/add
>>>>>>>>>> cpus at
>>>>>>>>>> runtime..
>>>>>>>>>>
>>>>>>>>>> Can you give this branch a try?
>>>>>>>>>>
>>>>>>>>>
>>>>>>>>> OK, you seem to be well again, nice to hear.
>>>>>>>>>
>>>>>>>>> I was doing the whole week spring-cleaning in the apartment of 
>>>>>>>>> my parents.
>>>>>>>>> Now, I have some minutes for a compilation run.
>>>>>>>>>
>>>>>>>>> I guess "cpufreq: Call __cpufreq_governor() with correct 
>>>>>>>>> policy->cpus
>>>>>>>>> mask" could be the correct fix, but will try the GIT branch 
>>>>>>>>> you have
>>>>>>>>> mentioned.
>>>>>>>>>
>>>>>>>>> - Sedat -
>>>>>>>>>
>>>>>>>>> [1]
>>>>>>>>> http://git.kernel.org/cgit/linux/kernel/git/rafael/linux-pm.git/commit/?h=linux-next&id=e4969ebac83fdea78d89c779331396728a4e6199 
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>
>>>>>>>> Both BROKEN here, specific pm-next commitid and pulling
>>>>>>>> pm.git#linux-next into next-20130411 (see attached files).
>>>>>>>>
>>>>>>>> Is "cpufreq: convert cpufreq_driver to using RCU" the root 
>>>>>>>> cause of this
>>>>>>>> all?
>>>>>>>>
>>>>>>>
>>>>>>> [ CC Nathan ]
>>>>>>>
>>>>>>> NO, wrong assumption.
>>>>>>>
>>>>>>> 2013-04-12 18:04 Sedat Dilek        o [revert-cpufreq-rcu] Revert
>>>>>>> "cpufreq: convert cpufreq_driver to using RCU"
>>>>>>> 2013-04-12 18:04 Sedat Dilek        o Revert "cpufreq: Call
>>>>>>> __cpufreq_governor() with correct policy->cpus mask"
>>>>>>> 2013-04-11 23:24 Rafael J. Wysocki  M─┐ [pm-next-079576f] Merge 
>>>>>>> branch
>>>>>>> 'pm-cpufreq-next' into linux-next
>>>>>>>
>>>>>>> - Sedat -
>>>>>>>
>>>>>>>
>>>>>>>> - Sedat -
>>>>>>>>
>>>>>>>> [1]
>>>>>>>> http://git.kernel.org/cgit/linux/kernel/git/rafael/linux-pm.git/commit/?h=linux-next&id=5800043b2488a1c4c6e859af860644d37419d58b 
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>>>> -- 
>>>>>>>>>> viresh
>>>>>>
>>>>>> [ TO Dirk (Author of Intel pstate driver) ]
>>>>>>
>>>>>> With CONFIG_X86_INTEL_PSTATE=n (unset) I do not see the call-trace!
>>>>>>
>>>>>> My kernel-config and dmesg are attached.
>>>>>
>>>>> You're seeing a trouble with a new driver, then, so that's not a 
>>>>> regression.
>>>>>
>>>
>>> This IS a regression.
>>>
>>> If the intel_pstate driver is being used __cpufreq_governor() should 
>>> NOT be
>>> called intel_pstate does not implement the target() callback.
>>>
>>> Nathan's commit 5800043b2 changed the fence around the call to
>>> __cpufreq_governor() in __cpufreq_remove_dev() here is the relevant 
>>> hunk.
>>>
>>> @@ -1007,9 +1068,12 @@ static int __cpufreq_remove_dev(struct device 
>>> *dev,
>>> struct subsys_interface *sif
>>>      unsigned int cpu = dev->id, ret, cpus;
>>>      unsigned long flags;
>>>      struct cpufreq_policy *data;
>>> +    struct cpufreq_driver *driver;
>>>      struct kobject *kobj;
>>>      struct completion *cmp;
>>>      struct device *cpu_dev;
>>> +    bool has_target;
>>> +    int (*exit)(struct cpufreq_policy *policy);
>>>
>>>      pr_debug("%s: unregistering CPU %u\n", __func__, cpu);
>>>
>>> @@ -1025,14 +1089,19 @@ static int __cpufreq_remove_dev(struct 
>>> device *dev,
>>> struct subsys_interface *sif
>>>          return -EINVAL;
>>>      }
>>>
>>> -    if (cpufreq_driver->target)
>>> +    rcu_read_lock();
>>> +    driver = rcu_dereference(cpufreq_driver);
>>> +    has_target = driver->target ? true : false;
>>> +    exit = driver->exit;
>>> +    if (has_target)
>>>          __cpufreq_governor(data, CPUFREQ_GOV_STOP);
>>>
>>>  #ifdef CONFIG_HOTPLUG_CPU
>>> -    if (!cpufreq_driver->setpolicy)
>>> +    if (!driver->setpolicy)
>>>          strncpy(per_cpu(cpufreq_cpu_governor, cpu),
>>>              data->governor->name, CPUFREQ_NAME_LEN);
>>>  #endif
>>> +    rcu_read_unlock();
>>>
>>>      WARN_ON(lock_policy_rwsem_write(cpu));
>>>      cpus = cpumask_weight(data->cpus);
>>>
>>
>> I am not clear at what is at issue.  Are you saying 
>> __cpufreq_governor can
>> change the value of cpufreq_driver->target?  I hadn't thought that 
>> was allowed
>> but if it is the code would need to be fixed.
>>
>
> Sorry I think pointing to your patch may have red herring see viresh's 
> mail.
>
> The issue is that __cpufreq_governor() is being called when 
> intel_pstate is the
> scaling driver intel_pstate does not implement ->target(). From the stack
> trace it looked like this was happening in __cpufreq_remove_dev() so I 
> "assumed"
> it was the first instance of the target fence that was failing.
>
> I am rebuilding using the next tree with viresh's patch I will let you 
> know what
> I find sorry for the noise.
>
> --Dirk
>> Nate
>
No worries.  I would rather see extra noise from linux-next then extra 
bugs in the mainline.
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