Date:	Wed, 05 Mar 2014 17:10:01 -0800
From:	Saravana Kannan <skannan@...eaurora.org>
To:	"Rafael J. Wysocki" <rjw@...ysocki.net>
CC:	Viresh Kumar <viresh.kumar@...aro.org>,
	linaro-kernel@...ts.linaro.org, cpufreq@...r.kernel.org,
	linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org,
	srivatsa.bhat@...ux.vnet.ibm.com
Subject: Re: [PATCH V2 3/3] cpufreq: initialize governor for a new policy
 under policy->rwsem

On 03/05/2014 05:06 PM, Rafael J. Wysocki wrote:
> On Thursday, March 06, 2014 02:04:39 AM Rafael J. Wysocki wrote:
>> On Tuesday, March 04, 2014 11:44:01 AM Viresh Kumar wrote:
>>> policy->rwsem is used to lock access to all parts of code modifying struct
>>> cpufreq_policy but wasn't used on a new policy created from __cpufreq_add_dev().
>>>
>>> Because of which if we call cpufreq_update_policy() repeatedly on one CPU and do
>>> offline/online of another CPU then we might see these crashes:
>>>
>>> Unable to handle kernel NULL pointer dereference at virtual address 00000020
>>> pgd = c0003000
>>> [00000020] *pgd=80000000004003, *pmd=00000000
>>> Internal error: Oops: 206 [#1] PREEMPT SMP ARM
>>>
>>> PC is at __cpufreq_governor+0x10/0x1ac
>>> LR is at cpufreq_update_policy+0x114/0x150
>>>
>>> ---[ end trace f23a8defea6cd706 ]---
>>> Kernel panic - not syncing: Fatal exception
>>> CPU0: stopping
>>> CPU: 0 PID: 7136 Comm: mpdecision Tainted: G      D W    3.10.0-gd727407-00074-g979ede8 #396
>>>
>>> [<c0afe180>] (notifier_call_chain+0x40/0x68) from [<c02a23ac>] (__blocking_notifier_call_chain+0x40/0x58)
>>> [<c02a23ac>] (__blocking_notifier_call_chain+0x40/0x58) from [<c02a23d8>] (blocking_notifier_call_chain+0x14/0x1c)
>>> [<c02a23d8>] (blocking_notifier_call_chain+0x14/0x1c) from [<c0803c68>] (cpufreq_set_policy+0xd4/0x2b8)
>>> [<c0803c68>] (cpufreq_set_policy+0xd4/0x2b8) from [<c0803e7c>] (cpufreq_init_policy+0x30/0x98)
>>> [<c0803e7c>] (cpufreq_init_policy+0x30/0x98) from [<c0805a18>] (__cpufreq_add_dev.isra.17+0x4dc/0x7a4)
>>> [<c0805a18>] (__cpufreq_add_dev.isra.17+0x4dc/0x7a4) from [<c0805d38>] (cpufreq_cpu_callback+0x58/0x84)
>>> [<c0805d38>] (cpufreq_cpu_callback+0x58/0x84) from [<c0afe180>] (notifier_call_chain+0x40/0x68)
>>> [<c0afe180>] (notifier_call_chain+0x40/0x68) from [<c02812dc>] (__cpu_notify+0x28/0x44)
>>> [<c02812dc>] (__cpu_notify+0x28/0x44) from [<c0aeed90>] (_cpu_up+0xf4/0x1dc)
>>> [<c0aeed90>] (_cpu_up+0xf4/0x1dc) from [<c0aeeed4>] (cpu_up+0x5c/0x78)
>>> [<c0aeeed4>] (cpu_up+0x5c/0x78) from [<c0aec808>] (store_online+0x44/0x74)
>>> [<c0aec808>] (store_online+0x44/0x74) from [<c03a40f4>] (sysfs_write_file+0x108/0x14c)
>>> [<c03a40f4>] (sysfs_write_file+0x108/0x14c) from [<c03517d4>] (vfs_write+0xd0/0x180)
>>> [<c03517d4>] (vfs_write+0xd0/0x180) from [<c0351ca8>] (SyS_write+0x38/0x68)
>>> [<c0351ca8>] (SyS_write+0x38/0x68) from [<c0205de0>] (ret_fast_syscall+0x0/0x30)
>>>
>>> Fix these by taking locks at appropriate places in __cpufreq_add_dev() as well.
>>>
>>> Reported-by: Saravana Kannan <skannan@...eaurora.org>
>>> Suggested-by: Srivatsa S. Bhat <srivatsa.bhat@...ux.vnet.ibm.com>
>>> Signed-off-by: Viresh Kumar <viresh.kumar@...aro.org>
>>
>> I've rebased this one on top of 3.14-rc5 and queued it up for 3.14-rc6.
>>
>> Please check the bleeding-edge branch for the result.
>
> Actually, I think I'll queue up [2-3/3] for 3.14-rc6 instead.
>

Pretty close to having this tested and reported back. So, if you can 
wait, that would be better. Should probably see an email by Fri evening PST.

-Saravana


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