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SubjectRe: [PATCH 01/18] led-triggers: create a trigger for CPU activity
On 4/17/2012 3:53 AM, Bryan Wu wrote:
> +static int __init ledtrig_cpu_init(void)
> +{
> + int cpu;
> +
> + /* Supports up to 9999 cpu cores */
> + BUILD_BUG_ON(CONFIG_NR_CPUS > 9999);
> +
> + /*
> + * Registering CPU led trigger for each CPU cores here
> + * ignores CPU hotplug, but after this CPU hotplug works
> + * fine with this trigger.
> + */
> + for_each_possible_cpu(cpu) {
> + struct led_trigger *trig;
> + char *name = per_cpu(trig_name, cpu);
> + struct rw_semaphore *lock = &per_cpu(trig_lock, cpu);
> +
> + init_rwsem(lock);

What is this lock protecting?

> +
> + snprintf(name, MAX_NAME_LEN, "cpu%d", cpu);
> +
> + down_write(lock);
> + led_trigger_register_simple(name, &trig);
> + per_cpu(cpu_trig, cpu) = trig;
> + up_write(lock);

This is the only place it is locked and unlocked.

I think the previous comment was about how led_trigger_register_simple()
exposed a live trigger but it wasn't assigned to the per_cpu variable
yet. Can we not just reorder the assignment so we have

struct led_trigger *trig = NULL;
...
per_cpu(cpu_trig, cpu) = trig;
led_trigger_register_simple();

?

--
Sent by an employee of the Qualcomm Innovation Center, Inc.
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum.



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