Re: [PATCH -next 1/2] cpufreq: powernv: Move smp_call_function_any() out of irq safe block

[Akshay Adiga]

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@xxxxxxxxxxxxxxxxxxxx>
> > Signed-off-by: Akshay Adiga <akshay.adiga@xxxxxxxxxxxxxxxxxx>
> > ---
> > 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.