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Subject: Re: [PATCH] cpufreq: powernv: Fix the hardlockup by synchronus
 smp_call in timer interrupt
To:     Stewart Smith <stewart@linux.ibm.com>, rjw@rjwysocki.net,
        viresh.kumar@linaro.org
References: <1524544906-31512-1-git-send-email-shilpa.bhat@linux.vnet.ibm.com>
 <87y3hdb36b.fsf@linux.vnet.ibm.com>
Cc:     npiggin@gmail.com, benh@kernel.crashing.org, mpe@ellerman.id.au,
        linux-pm@vger.kernel.org, linuxppc-dev@lists.ozlabs.org,
        linux-kernel@vger.kernel.org, ppaidipe@linux.vnet.ibm.com,
        svaidy@linux.vnet.ibm.com
From:   Shilpasri G Bhat <shilpa.bhat@linux.vnet.ibm.com>
Date:   Tue, 24 Apr 2018 10:54:18 +0530
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Hi,

On 04/24/2018 10:40 AM, Stewart Smith wrote:
> Shilpasri G Bhat <shilpa.bhat@linux.vnet.ibm.com> writes:
>> gpstate_timer_handler() uses synchronous smp_call to set the pstate
>> on the requested core. This causes the below hard lockup:
>>
>> [c000003fe566b320] [c0000000001d5340] smp_call_function_single+0x110/0x180 (unreliable)
>> [c000003fe566b390] [c0000000001d55e0] smp_call_function_any+0x180/0x250
>> [c000003fe566b3f0] [c000000000acd3e8] gpstate_timer_handler+0x1e8/0x580
>> [c000003fe566b4a0] [c0000000001b46b0] call_timer_fn+0x50/0x1c0
>> [c000003fe566b520] [c0000000001b4958] expire_timers+0x138/0x1f0
>> [c000003fe566b590] [c0000000001b4bf8] run_timer_softirq+0x1e8/0x270
>> [c000003fe566b630] [c000000000d0d6c8] __do_softirq+0x158/0x3e4
>> [c000003fe566b710] [c000000000114be8] irq_exit+0xe8/0x120
>> [c000003fe566b730] [c000000000024d0c] timer_interrupt+0x9c/0xe0
>> [c000003fe566b760] [c000000000009014] decrementer_common+0x114/0x120
>> --- interrupt: 901 at doorbell_global_ipi+0x34/0x50
>> LR = arch_send_call_function_ipi_mask+0x120/0x130
>> [c000003fe566ba50] [c00000000004876c] arch_send_call_function_ipi_mask+0x4c/0x130 (unreliable)
>> [c000003fe566ba90] [c0000000001d59f0] smp_call_function_many+0x340/0x450
>> [c000003fe566bb00] [c000000000075f18] pmdp_invalidate+0x98/0xe0
>> [c000003fe566bb30] [c0000000003a1120] change_huge_pmd+0xe0/0x270
>> [c000003fe566bba0] [c000000000349278] change_protection_range+0xb88/0xe40
>> [c000003fe566bcf0] [c0000000003496c0] mprotect_fixup+0x140/0x340
>> [c000003fe566bdb0] [c000000000349a74] SyS_mprotect+0x1b4/0x350
>> [c000003fe566be30] [c00000000000b184] system_call+0x58/0x6c
>>
>> Fix this by using the asynchronus smp_call in the timer interrupt handler.
>> We don't have to wait in this handler until the pstates are changed on
>> the core. This change will not have any impact on the global pstate
>> ramp-down algorithm.
>>
>> Reported-by: Nicholas Piggin <npiggin@gmail.com>
>> Reported-by: Pridhiviraj Paidipeddi <ppaidipe@linux.vnet.ibm.com>
>> Signed-off-by: Shilpasri G Bhat <shilpa.bhat@linux.vnet.ibm.com>
>> ---
>>  drivers/cpufreq/powernv-cpufreq.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/cpufreq/powernv-cpufreq.c b/drivers/cpufreq/powernv-cpufreq.c
>> index 0591874..7e0c752 100644
>> --- a/drivers/cpufreq/powernv-cpufreq.c
>> +++ b/drivers/cpufreq/powernv-cpufreq.c
>> @@ -721,7 +721,7 @@ void gpstate_timer_handler(struct timer_list *t)
>>  	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);
>> +	smp_call_function_any(policy->cpus, set_pstate, &freq_data, 0);
>>  }
> 
> Should this have:
> Fixes: eaa2c3aeef83f
> and CC stable v4.7+ ?
> 

Yeah this is required.

Fixes: eaa2c3aeef83 (cpufreq: powernv: Ramp-down global pstate slower than
local-pstate)

Thanks and Regards,
Shilpa