On Sun, 2013-06-23 at 19:08 +0530, Srivatsa S. Bhat wrote:
Just to make the code a little cleaner, can you add:
> diff --git a/kernel/cpu.c b/kernel/cpu.c
> index 860f51a..e90d9d7 100644
> --- a/kernel/cpu.c
> +++ b/kernel/cpu.c
> @@ -63,6 +63,72 @@ static struct {
> .refcount = 0,
> };
>
> +#ifdef CONFIG_DEBUG_HOTPLUG_CPU
> +
> +static DEFINE_PER_CPU(unsigned long, atomic_reader_refcnt);
> +
> +static int current_is_hotplug_safe(const struct cpumask *mask)
> +{
> +
> + /* If we are not dealing with cpu_online_mask, don't complain. */
> + if (mask != cpu_online_mask)
> + return 1;
> +
> + /* If this is the task doing hotplug, don't complain. */
> + if (unlikely(current == cpu_hotplug.active_writer))
> + return 1;
> +
> + /* If we are in early boot, don't complain. */
> + if (system_state != SYSTEM_RUNNING)
> + return 1;
> +
> + /*
> + * Check if the current task is in atomic context and it has
> + * invoked get_online_cpus_atomic() to synchronize with
> + * CPU Hotplug.
> + */
> + if (preempt_count() || irqs_disabled())
> + return this_cpu_read(atomic_reader_refcnt);
> + else
> + return 1; /* No checks for non-atomic contexts for now */
> +}
> +
> +static inline void warn_hotplug_unsafe(void)
> +{
> + WARN_ONCE(1, "Must use get/put_online_cpus_atomic() to synchronize"
> + " with CPU hotplug\n");
> +}
> +
> +/*
> + * Check if the task (executing in atomic context) has the required protection
> + * against CPU hotplug, while accessing the specified cpumask.
> + */
> +void check_hotplug_safe_cpumask(const struct cpumask *mask)
> +{
> + if (!current_is_hotplug_safe(mask))
> + warn_hotplug_unsafe();
> +}
> +EXPORT_SYMBOL_GPL(check_hotplug_safe_cpumask);
> +
> +/*
> + * Similar to check_hotplug_safe_cpumask(), except that we don't complain
> + * if the task (executing in atomic context) is testing whether the CPU it
> + * is executing on is online or not.
> + *
> + * (A task executing with preemption disabled on a CPU, automatically prevents
> + * offlining that CPU, irrespective of the actual implementation of CPU
> + * offline. So we don't enforce holding of get_online_cpus_atomic() for that
> + * case).
> + */
> +void check_hotplug_safe_cpu(unsigned int cpu, const struct cpumask *mask)
> +{
> + if(!current_is_hotplug_safe(mask) && cpu != smp_processor_id())
> + warn_hotplug_unsafe();
> +}
> +EXPORT_SYMBOL_GPL(check_hotplug_safe_cpu);
> +
static inline void atomic_reader_refcnt_inc(void)
{
this_cpu_inc(atomic_reader_refcnt);
}
static inline void atomic_reader_refcnt_dec(void)
{
this_cpu_dec(atomic_reader_refcnt);
}
#else
static inline void atomic_reader_refcnt_inc(void)
{
}
static inline void atomic_reader_refcnt_dec(void)
{
}
#endif
> +#endif
> +
> void get_online_cpus(void)
> {
> might_sleep();
> @@ -189,13 +255,22 @@ unsigned int get_online_cpus_atomic(void)
> * from going offline.
> */
> preempt_disable();
> +
> +#ifdef CONFIG_DEBUG_HOTPLUG_CPU
> + this_cpu_inc(atomic_reader_refcnt);
> +#endif
Replace the #ifdef with just:
atomic_reader_refcnt_inc();
> return smp_processor_id();
> }
> EXPORT_SYMBOL_GPL(get_online_cpus_atomic);
>
> void put_online_cpus_atomic(void)
> {
> +
> +#ifdef CONFIG_DEBUG_HOTPLUG_CPU
> + this_cpu_dec(atomic_reader_refcnt);
> +#endif
And
atomic_reader_refcnt_dec();
-- Steve
> preempt_enable();
> +
> }
> EXPORT_SYMBOL_GPL(put_online_cpus_atomic);
>
--
To unsubscribe from this list: send the line "unsubscribe linux-arch" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
