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Date:   Wed, 25 Apr 2018 14:47:01 +0530
From:   Viresh Kumar <viresh.kumar@linaro.org>
To:     Shilpasri G Bhat <shilpa.bhat@linux.vnet.ibm.com>
Cc:     rjw@rjwysocki.net, npiggin@gmail.com, linux-pm@vger.kernel.org,
        ppaidipe@linux.vnet.ibm.com, linuxppc-dev@lists.ozlabs.org,
        linux-kernel@vger.kernel.org, svaidy@linux.vnet.ibm.com,
        stable@vger.kernel.org
Subject: Re: [PATCH V2] cpufreq: powernv: Fix the hardlockup by synchronus
 smp_call in timer interrupt
Message-ID: <20180425091701.kxxslgalw3sdpiym@vireshk-i7>
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On 25-04-18, 14:32, Shilpasri G Bhat wrote:
> 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
> [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
> 
> One way to avoid this is removing the smp-call. We can ensure that the timer
> always runs on one of the policy-cpus. If the timer gets migrated to a
> cpu outside the policy then re-queue it back on the policy->cpus. This way
> we can get rid of the smp-call which was being used to set the pstate
> on the policy->cpus.
> 
> Fixes: 7bc54b652f13 (timers, cpufreq/powernv: Initialize the gpstate timer as pinned)
> Cc: <stable@vger.kernel.org>        [4.8+]
> 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>
> ---
> Changes from V1:
> - Remove smp_call in the pstate handler.
> 
>  drivers/cpufreq/powernv-cpufreq.c | 23 ++++++++++++++++++++---
>  1 file changed, 20 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/cpufreq/powernv-cpufreq.c b/drivers/cpufreq/powernv-cpufreq.c
> index 71f8682..dc8ffb5 100644
> --- a/drivers/cpufreq/powernv-cpufreq.c
> +++ b/drivers/cpufreq/powernv-cpufreq.c
> @@ -679,6 +679,25 @@ void gpstate_timer_handler(struct timer_list *t)
>  
>  	if (!spin_trylock(&gpstates->gpstate_lock))
>  		return;
> +	/*
> +	 * If the timer has migrated to the different cpu then bring
> +	 * it back to one of the policy->cpus
> +	 */
> +	if (!cpumask_test_cpu(raw_smp_processor_id(), policy->cpus)) {
> +		/*
> +		 * Timer should be deleted if policy is inactive.
> +		 * If policy is active then re-queue on one of the
> +		 * policy->cpus.
> +		 */

This looks racy. Shouldn't you guarantee that the timer is already
removed in a synchronous way before de-activating the policy ?

> +		if (!cpumask_empty(policy->cpus)) {
> +			gpstates->timer.expires = jiffies +
> +						msecs_to_jiffies(1);
> +			add_timer_on(&gpstates->timer,
> +					cpumask_first(policy->cpus));
> +		}
> +		spin_unlock(&gpstates->gpstate_lock);
> +		return;
> +	}
>  
>  	/*
>  	 * If PMCR was last updated was using fast_swtich then
> @@ -718,10 +737,8 @@ void gpstate_timer_handler(struct timer_list *t)
>  	if (gpstate_idx != gpstates->last_lpstate_idx)
>  		queue_gpstate_timer(gpstates);
>  
> +	set_pstate(&freq_data);
>  	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);
>  }
>  
>  /*
> -- 
> 1.8.3.1

-- 
viresh