[PATCH 02/19] cpu/hotplug: Avoid trying to bring up CPUs that are already online

[Jinjie Ruan]

在 2026/9/8 0:40, Will Deacon 写道:
> There's little point trying to bring up a CPU that is already online.
> Although _cpu_up() handles this case by doing nothing (because the
> target state has already been reached), it's wasted effort when we can
> easily elide the call to cpu_up() in the first place.
> 
> Check that the target CPU isn't already online before invoking cpu_up()
> from cpuhp_bringup_mask().
> 
> Signed-off-by: Will Deacon <will at kernel.org>
> ---
>  kernel/cpu.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/cpu.c b/kernel/cpu.c
> index 198c929c452a..97a9bfe4edad 100644
> --- a/kernel/cpu.c
> +++ b/kernel/cpu.c
> @@ -1769,7 +1769,8 @@ static void __init cpuhp_bringup_mask(const struct cpumask *mask, unsigned int n
>  	for_each_cpu(cpu, mask) {
>  		struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, cpu);
>  
> -		if (cpu_up(cpu, target) && can_rollback_cpu(st)) {
> +		if (!cpu_online(cpu) && cpu_up(cpu, target) &&
> +		    can_rollback_cpu(st)) {

Make sense to me.

Reviewed-by: Jinjie Ruan <ruanjinjie at huawei.com>

>  			/*
>  			 * If this failed then cpu_up() might have only
>  			 * rolled back to CPUHP_BP_KICK_AP for the final