Subject: [SMP BUG?] the return value of is_smp() is bug?

From: [email-masked] (long.wanglong)
Date: Mon, 1 Sep 2014 18:00:58 +0800

On 2014/9/1 13:49, Wang Long wrote:
> 
> Hi,all
> 
> In kernel 3.17-rc2, when i set CONFIG_HAVE_SMP = y and CONFIG_SMP_ON_UP = y 
> in .config file. the secondary core can not boot.
> 
> when i set CONFIG_HAVE_SMP = y and CONFIG_SMP_ON_UP = n in .config file,
> the secondary core can boot.
> 
> But this does not happen in kernel 3.10 lts kernel, Whether the 
> CONFIG_SMP_ON_UP is set yes or no ,the secondary core can boot.
> 
> Does the meaning of CONFIG_SMP_ON_UP changed or this is a bug in kernel 3.17-rc2 ? 
> 
> 

hi Arnd

In above two cases, i also set  CONFIG_SMP = y. in addtion,
the CONFIG_SMP_ON_UP depends on CONFIG_SMP. when set
CONFIG_SMP_ON_UP = y, the value of CONFIG_SMP must be y.

> I write the following patch to test the return value of is_smp().
> 
> ----------------------------------------
> 
> Signed-off-by: Wang Long <[email-masked]>
> ---
>  arch/arm/kernel/setup.c |    5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/arch/arm/kernel/setup.c b/arch/arm/kernel/setup.c
> index 84db893d..fbeb67f 100644
> --- a/arch/arm/kernel/setup.c
> +++ b/arch/arm/kernel/setup.c
> @@ -925,6 +925,11 @@ void __init setup_arch(char **cmdline_p)
>  	arm_dt_init_cpu_maps();
>  	psci_init();
>  #ifdef CONFIG_SMP
> +	
> +	if (is_smp() == 1)
> +		printk("is_smp() return true;\n");
> +	else if (is_smp() == 0)
> +		printk("is_smp() return false;\n");
>  	if (is_smp()) {
>  		if (!mdesc->smp_init || !mdesc->smp_init()) {
>  			if (psci_smp_available())
> 
> kernel version: 3.17-rc2
> 
> config:     set CONFIG_HAVE_SMP = y and CONFIG_SMP_ON_UP = y
> command:    # qemu-system-arm -M vexpress-a9 -smp 2  -m 128M -kernel arch/arm/boot/zImage -nographic
> The output:
> 
> ..........
> is_smp() return false;
> CPU: Testing write buffer coherency: ok
> missing device node for CPU 0
> CPU0: thread -1, cpu 0, socket 0, mpidr 80000000
> Setting up static identity map for 0x604643d8 - 0x60464430
> Brought up 1 CPUs
> SMP: Total of 1 processors activated.
> CPU: All CPU(s) started in SVC mode.
> ...........
> 
> config:     set CONFIG_HAVE_SMP = y and not set CONFIG_SMP_ON_UP 
> command:    # qemu-system-arm -M vexpress-a9 -smp 2  -m 128M -kernel arch/arm/boot/zImage -nographic
> The output:
> 
> .....
>  Memory policy: Data cache writealloc
> is_smp() return true;
> sched_clock: 32 bits at 24MHz, resolution 41ns, wraps every 178956969942ns
> ......
> ......
> CPU: Testing write buffer coherency: ok
> missing device node for CPU 0
> missing device node for CPU 1
> CPU0: thread -1, cpu 0, socket 0, mpidr 80000000
> Setting up static identity map for 0x60463ef8 - 0x60463f50
> CPU1: Booted secondary processor
> CPU1: thread -1, cpu 1, socket 0, mpidr 80000001
> Brought up 2 CPUs
> SMP: Total of 2 processors activated.
> CPU: All CPU(s) started in SVC mode.
> devtmpfs: initialized
> .......
> 
> Any ideas?
> 
>