Re: [PATCH] powerpc:85xx: fix timebase sync issue when CONFIG_HOTPLUG_CPU=n

[Xiaoming Ni <nixiaoming@huawei.com>]

On 2021/9/26 10:51, Xiaoming Ni wrote:
> When CONFIG_SMP=y, timebase synchronization is required when the second
>   kernel is started.
> 	arch/powerpc/kernel/smp.c:
> 	int __cpu_up(unsigned int cpu, struct task_struct *tidle)
> 	{
> 		...
> 		if (smp_ops->give_timebase)
> 			smp_ops->give_timebase();
> 		...
> 	}
> 
> 	void start_secondary(void *unused)
> 	{
> 		...
> 		if (smp_ops->take_timebase)
> 			smp_ops->take_timebase();
> 		...
> 	}
> 
> When CONFIG_HOTPLUG_CPU=n and CONFIG_KEXEC_CORE=n,
>   smp_85xx_ops.give_timebase is NULL,
>   smp_85xx_ops.take_timebase is NULL,
> As a result, the timebase is not synchronized.
> 
> Timebase  synchronization does not depend on CONFIG_HOTPLUG_CPU.
> 
> Fixes: 56f1ba280719 ("powerpc/mpc85xx: refactor the PM operations")
> Cc: stable@vger.kernel.org #v4.6
> Signed-off-by: Xiaoming Ni <nixiaoming@huawei.com>
> ---
>   arch/powerpc/platforms/85xx/Makefile         | 2 +-
>   arch/powerpc/platforms/85xx/mpc85xx_pm_ops.c | 4 ++++
>   arch/powerpc/platforms/85xx/smp.c            | 9 ++++-----
>   3 files changed, 9 insertions(+), 6 deletions(-)
> 
> diff --git a/arch/powerpc/platforms/85xx/Makefile b/arch/powerpc/platforms/85xx/Makefile
> index 60e4e97a929d..71ce1f6b6966 100644
> --- a/arch/powerpc/platforms/85xx/Makefile
> +++ b/arch/powerpc/platforms/85xx/Makefile
> @@ -3,7 +3,7 @@
>   # Makefile for the PowerPC 85xx linux kernel.
>   #
>   obj-$(CONFIG_SMP) += smp.o
> -obj-$(CONFIG_FSL_PMC)		  += mpc85xx_pm_ops.o
> +obj-$(CONFIG_SMP) += mpc85xx_pm_ops.o
>   
>   obj-y += common.o
>   
> diff --git a/arch/powerpc/platforms/85xx/mpc85xx_pm_ops.c b/arch/powerpc/platforms/85xx/mpc85xx_pm_ops.c
> index 7c0133f558d0..a5656b3e9701 100644
> --- a/arch/powerpc/platforms/85xx/mpc85xx_pm_ops.c
> +++ b/arch/powerpc/platforms/85xx/mpc85xx_pm_ops.c
> @@ -17,6 +17,7 @@
>   
>   static struct ccsr_guts __iomem *guts;
>   
> +#ifdef CONFIG_FSL_PMC
>   static void mpc85xx_irq_mask(int cpu)
>   {
>   
> @@ -49,6 +50,7 @@ static void mpc85xx_cpu_up_prepare(int cpu)
>   {
>   
>   }
> +#endif
>   
>   static void mpc85xx_freeze_time_base(bool freeze)
>   {
> @@ -76,10 +78,12 @@ static const struct of_device_id mpc85xx_smp_guts_ids[] = {
>   
>   static const struct fsl_pm_ops mpc85xx_pm_ops = {
>   	.freeze_time_base = mpc85xx_freeze_time_base,
> +#ifdef CONFIG_FSL_PMC
>   	.irq_mask = mpc85xx_irq_mask,
>   	.irq_unmask = mpc85xx_irq_unmask,
>   	.cpu_die = mpc85xx_cpu_die,
>   	.cpu_up_prepare = mpc85xx_cpu_up_prepare,
> +#endif
>   };
>   
>   int __init mpc85xx_setup_pmc(void)
> diff --git a/arch/powerpc/platforms/85xx/smp.c b/arch/powerpc/platforms/85xx/smp.c
> index c6df294054fe..349298cd9671 100644
> --- a/arch/powerpc/platforms/85xx/smp.c
> +++ b/arch/powerpc/platforms/85xx/smp.c
> @@ -40,7 +40,6 @@ struct epapr_spin_table {
>   	u32	pir;
>   };
>   
> -#ifdef CONFIG_HOTPLUG_CPU
>   static u64 timebase;
>   static int tb_req;
>   static int tb_valid;
> @@ -112,6 +111,7 @@ static void mpc85xx_take_timebase(void)
>   	local_irq_restore(flags);
>   }
>   
> +#ifdef CONFIG_HOTPLUG_CPU
>   static void smp_85xx_cpu_offline_self(void)
>   {
>   	unsigned int cpu = smp_processor_id();
> @@ -499,17 +499,16 @@ void __init mpc85xx_smp_init(void)
>   #ifdef CONFIG_FSL_CORENET_RCPM
>   	fsl_rcpm_init();
>   #endif
> -
> -#ifdef CONFIG_FSL_PMC
> -	mpc85xx_setup_pmc();
>   #endif
> +	mpc85xx_setup_pmc();
>   	if (qoriq_pm_ops) {
>   		smp_85xx_ops.give_timebase = mpc85xx_give_timebase;
>   		smp_85xx_ops.take_timebase = mpc85xx_take_timebase;
> +#ifdef CONFIG_HOTPLUG_CPU
>   		smp_85xx_ops.cpu_offline_self = smp_85xx_cpu_offline_self;
>   		smp_85xx_ops.cpu_die = qoriq_cpu_kill;
> -	}
>   #endif
> +	}
>   	smp_ops = &smp_85xx_ops;
>   
>   #ifdef CONFIG_KEXEC_CORE
> 


I found inconsistent time values on different CPUs on my mpc8572 and 
used this patch to fix it.
But today I found out in ppc64 testing that this patch causes the system 
to trigger oops in the function mpc85xx_freeze_time_base(): the variable 
"guts" is a null pointer.

I'm sorry to bother you.
I'll fix it and resend v2 later,

Thanks
Xiaoming Ni