ACK: [SRU][Bionic][PATCH 1/1] cpufreq: powernv: Fix hardlockup due to synchronous smp_call in timer interrupt

[Kleber Souza]

On 05/18/18 16:23, Joseph Salisbury wrote:
> From: Shilpasri G Bhat <shilpa.bhat at linux.vnet.ibm.com>
> 
> BugLink: http://bugs.launchpad.net/bugs/1768898
> 
> gpstate_timer_handler() uses synchronous smp_call to set the pstate
> on the requested core. This causes the below hard lockup:
> 
>   smp_call_function_single+0x110/0x180 (unreliable)
>   smp_call_function_any+0x180/0x250
>   gpstate_timer_handler+0x1e8/0x580
>   call_timer_fn+0x50/0x1c0
>   expire_timers+0x138/0x1f0
>   run_timer_softirq+0x1e8/0x270
>   __do_softirq+0x158/0x3e4
>   irq_exit+0xe8/0x120
>   timer_interrupt+0x9c/0xe0
>   decrementer_common+0x114/0x120
>   -- interrupt: 901 at doorbell_global_ipi+0x34/0x50
>   LR = arch_send_call_function_ipi_mask+0x120/0x130
>   arch_send_call_function_ipi_mask+0x4c/0x130
>   smp_call_function_many+0x340/0x450
>   pmdp_invalidate+0x98/0xe0
>   change_huge_pmd+0xe0/0x270
>   change_protection_range+0xb88/0xe40
>   mprotect_fixup+0x140/0x340
>   SyS_mprotect+0x1b4/0x350
>   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 at vger.kernel.org # v4.8+
> Reported-by: Nicholas Piggin <npiggin at gmail.com>
> Reported-by: Pridhiviraj Paidipeddi <ppaidipe at linux.vnet.ibm.com>
> Signed-off-by: Shilpasri G Bhat <shilpa.bhat at linux.vnet.ibm.com>
> Acked-by: Nicholas Piggin <npiggin at gmail.com>
> Acked-by: Viresh Kumar <viresh.kumar at linaro.org>
> Acked-by: Vaidyanathan Srinivasan <svaidy at linux.vnet.ibm.com>
> Signed-off-by: Michael Ellerman <mpe at ellerman.id.au>
> (cherry picked from commit c0f7f5b6c69107ca92909512533e70258ee19188)
> Signed-off-by: Joseph Salisbury <joseph.salisbury at canonical.com>
> ---
>  drivers/cpufreq/powernv-cpufreq.c | 14 +++++++++++---
>  1 file changed, 11 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/cpufreq/powernv-cpufreq.c b/drivers/cpufreq/powernv-cpufreq.c
> index 3738123..94235b6 100644
> --- a/drivers/cpufreq/powernv-cpufreq.c
> +++ b/drivers/cpufreq/powernv-cpufreq.c
> @@ -647,6 +647,16 @@ 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)) {
> +		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
> @@ -686,10 +696,8 @@ 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);
>  }
>  
>  /*
>