Re: [PATCH 03/19] cpu/hotplug: Avoid busy-polling on archs where cpu_relax() is a no-op

[Jinjie Ruan]

在 2026/9/11 20:57, Will Deacon 写道:
> On Fri, Sep 11, 2026 at 03:16:23PM +0800, Jinjie Ruan wrote:
>> 在 2026/9/8 0:40, Will Deacon 写道:
>>> diff --git a/kernel/cpu.c b/kernel/cpu.c
>>> index 97a9bfe4edad..d9fe204f02cb 100644
>>> --- a/kernel/cpu.c
>>> +++ b/kernel/cpu.c
>>> @@ -303,7 +303,13 @@ static inline void cpuhp_ap_update_sync_state(enum cpuhp_sync_state state)
>>>  	(void)atomic_xchg(st, state);
>>>  }
>>>  
>>> -void __weak arch_cpuhp_sync_state_poll(void) { cpu_relax(); }
>>> +void __weak arch_cpuhp_sync_state_poll(atomic_t *st, int old)
>>> +{
>>> +	if (old < SYNC_STATE_ALIVE)
>>> +		cpu_relax();
>>> +	else
>>> +		atomic_cond_read_relaxed(st, VAL != old);
>>> +}
>>
>> As sashiko pointed out, it seems that the else branch unreachable for
>> the call of cpuhp_wait_for_sync_state(cpu, SYNC_STATE_ALIVE,
>> SYNC_STATE_SHOULD_ONLINE), the old state can only be "SYNC_STATE_KICKED"
>> or "SYNC_STATE_SHOULD_DIE", which go the if branch.
> 
> Ah yes, it's a harmless leftover from my initial (failed) attempt to use
> cpuhp_wait_for_sync_state() in cpuhp_ap_sync_alive(). I can drop this
> part and reword the commit message.

Thanks, looking forward to your update — that will be nice.

> 
> Will