Re: [PATCH next v1 1/2] dump_stack: move cpu lock to printk.c

[John Ogness]

On 2021-06-01, Sergey Senozhatsky <senozhatsky@xxxxxxxxxxxx> wrote:
> On (21/05/31 18:20), John Ogness wrote:
>> +void printk_cpu_lock(unsigned int *cpu_store, unsigned long *flags)
>> +{
>> +	unsigned int cpu;
>> +
>> +	for (;;) {
>> +		cpu = get_cpu();
>> +
>> +		*cpu_store = atomic_read(&printk_cpulock_owner);
>> +
>> +		if (*cpu_store == -1) {
>> +			local_irq_save(*flags);
>
> Is there any particular reason this does
>
> 	preempt_disable();
> 	cpu = smp_processor_id();
> 	local_irq_safe();
>
> instead of
>
> 	local_irq_safe();
> 	cpu = raw_smp_processor_id();
>
> ?

If the lock is owned by another CPU, there is no need to disable
interrupts for this CPU. (The local_irq_save() is conditional.)

John Ogness