Re: [RESEND PATCH v5 04/12] smp: Use task-local IPI cpumask in smp_call_function_many_cond()

[Chuyi Zhou]

On 2026-05-21 11:26 p.m., Sebastian Andrzej Siewior wrote:
> On 2026-05-13 20:45:16 [+0800], Chuyi Zhou wrote:
>> diff --git a/kernel/smp.c b/kernel/smp.c
>> index 9e9dab3b0d51..630c8e5a635d 100644
>> --- a/kernel/smp.c
>> +++ b/kernel/smp.c
>> @@ -811,11 +849,18 @@ static void smp_call_function_many_cond(const struct cpumask *mask,
>>   	int cpu, last_cpu, this_cpu = smp_processor_id();
>>   	struct call_function_data *cfd;
>>   	bool wait = scf_flags & SCF_WAIT;
>> +	struct cpumask *cpumask, *task_mask;
>> +	bool preemptible_wait;
>>   	int nr_cpus = 0;
>>   	bool run_remote = false;
>>   
>>   	lockdep_assert_preemption_disabled();
>>   
>> +	task_mask = smp_task_ipi_mask(current);
>> +	preemptible_wait = task_mask;
>> +	cfd = this_cpu_ptr(&cfd_data);
>> +	cpumask = preemptible_wait ? task_mask : cfd->cpumask;
> 
> Is this a porting artifact? preemptible_wait is a bool while task_mask
> is a pointer which is always != NULL.
> 

Not exactly. The NULL fallback is intentional: smp_task_ipi_mask()
returns NULL for !CONFIG_PREEMPTION, and init_task may also not have an
allocated ipi_mask_ptr in the non-inlined case.

But you are right that the name is confusing in this preparatory patch.
Here it only means "task-local cpumask is available", not that the wait is
actually preemptible. I will drop this bool in this patch, and keep
the real preemptible wait condition in the later patch as:

    preemptible_wait = task_mask && preemptible();



> UP to here the patches and the code made sense.
> 
>> +
>>   	/*
>>   	 * Can deadlock when called with interrupts disabled.
>>   	 * We allow cpu's that are not yet online though, as no one else can
> 
> Sebastian