linux-kernel - Re: [PATCH -next 1/2] cpufreq: powernv: Move smp_call_function

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Date:	Tue, 3 May 2016 18:48:51 +0530
From:	Akshay Adiga <akshay.adiga@...ux.vnet.ibm.com>
To:	Viresh Kumar <viresh.kumar@...aro.org>
Cc:	rjw@...ysocki.net, linux-pm@...r.kernel.org,
	linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH -next 1/2] cpufreq: powernv: Move smp_call_function_any()
 out of irq safe block


Hi Viresh,

On 05/03/2016 05:19 PM, Viresh Kumar wrote:

> On 03-05-16, 15:10, Akshay Adiga wrote:
>> Fixing a WARN_ON caused by smp_call_function_any() when irq is disabled,
>> because of changes made in the patch
>> ('cpufreq: powernv: Ramp-down global pstate slower than local-pstate')
>> https://patchwork.ozlabs.org/patch/612058/
>>
>>   WARNING: CPU: 0 PID: 4 at kernel/smp.c:291
>> smp_call_function_single+0x170/0x180
>>
>>   Call Trace:
>>   [c0000007f648f9f0] [c0000007f648fa90] 0xc0000007f648fa90 (unreliable)
>>   [c0000007f648fa30] [c0000000001430e0] smp_call_function_any+0x170/0x1c0
>>   [c0000007f648fa90] [c0000000007b4b00]
>> powernv_cpufreq_target_index+0xe0/0x250
>>   [c0000007f648fb00] [c0000000007ac9dc]
>> __cpufreq_driver_target+0x20c/0x3d0
>>   [c0000007f648fbc0] [c0000000007b1b4c] od_dbs_timer+0xcc/0x260
>>   [c0000007f648fc10] [c0000000007b3024] dbs_work_handler+0x54/0xa0
>>   [c0000007f648fc50] [c0000000000c49a8] process_one_work+0x1d8/0x590
>>   [c0000007f648fce0] [c0000000000c4e08] worker_thread+0xa8/0x660
>>   [c0000007f648fd80] [c0000000000cca88] kthread+0x108/0x130
>>   [c0000007f648fe30] [c0000000000095e8] ret_from_kernel_thread+0x5c/0x74
>>
>> Moving smp_call_function_any() out of the critical section and changing
>> irq safe spinlocks to normal spinlocks.
>>
>> Reported-by: Abdul Haleem <abdhalee@...ux.vnet.linux.com>
>> Signed-off-by: Akshay Adiga <akshay.adiga@...ux.vnet.ibm.com>
>> ---
>> Patch is based on Rafael's linux-next
>>   drivers/cpufreq/powernv-cpufreq.c | 9 +++++----
>>   1 file changed, 5 insertions(+), 4 deletions(-)
>>
>> diff --git a/drivers/cpufreq/powernv-cpufreq.c b/drivers/cpufreq/powernv-cpufreq.c
>> index 144c732..1f0e20c 100644
>> --- a/drivers/cpufreq/powernv-cpufreq.c
>> +++ b/drivers/cpufreq/powernv-cpufreq.c
>> @@ -581,9 +581,10 @@ void gpstate_timer_handler(unsigned long data)
>>   	gpstates->last_gpstate = freq_data.gpstate_id;
>>   	gpstates->last_lpstate = freq_data.pstate_id;
>>   
>> +	spin_unlock(&gpstates->gpstate_lock);
>> +
>>   	/* Timer may get migrated to a different cpu on cpu hot unplug */
>>   	smp_call_function_any(policy->cpus, set_pstate, &freq_data, 1);
>> -	spin_unlock(&gpstates->gpstate_lock);
>>   }
>>   
>>   /*
>> @@ -596,7 +597,6 @@ static int powernv_cpufreq_target_index(struct cpufreq_policy *policy,
>>   {
>>   	struct powernv_smp_call_data freq_data;
>>   	unsigned int cur_msec, gpstate_id;
>> -	unsigned long flags;
>>   	struct global_pstate_info *gpstates = policy->driver_data;
>>   
>>   	if (unlikely(rebooting) && new_index != get_nominal_index())
>> @@ -607,7 +607,7 @@ static int powernv_cpufreq_target_index(struct cpufreq_policy *policy,
>>   
>>   	cur_msec = jiffies_to_msecs(get_jiffies_64());
>>   
>> -	spin_lock_irqsave(&gpstates->gpstate_lock, flags);
>> +	spin_lock(&gpstates->gpstate_lock);
> You don't necessarily have to write 'what you are doing' in the commit log, but
> tell us why you are doing that.
>
> Please explain, why is this changed and why will things continue to work
> without this.
>
Thanks for reviewing. I have tried to convey that in the first line of commit message,

"WARN_ON caused by smp_call_function_any() when irq is disabled,
because of changes made in the patch"

I see, i have not explained why i am changing irq safe spinlock to normal spinlock.
will add some explanation.