Re: [PATCH V2 3/4] oprofile: Abstract the perf-events backend

Will Deacon
2010-08-27T10:42:33Z

Hi Matt,

I'm still not happy with the init/exit alloc/free code:

On Thu, 2010-08-26 at 20:09 +0100, Matt Fleming wrote:

[...]

> +int oprofile_perf_init(void)
> +{
> + u32 counter_size = sizeof(struct op_counter_config);
> + int cpu;
> +
> + counter_config = kcalloc(perf_num_counters, counter_size, GFP_KERNEL);
> +
> + if (!counter_config) {
> + pr_info("oprofile: failed to allocate %d "
> + "counters\n", perf_num_counters);
> + return -ENOMEM;
> + }
> +
> + for_each_possible_cpu(cpu) {
> + perf_events[cpu] = kcalloc(perf_num_counters,
> + sizeof(struct perf_event *), GFP_KERNEL);
> + if (!perf_events[cpu]) {
> + pr_info("oprofile: failed to allocate %d perf events "
> + "for cpu %d\n", perf_num_counters, cpu);
> + while (--cpu >= 0)
> + kfree(perf_events[cpu]);
> + kfree(counter_config);
> + return -ENOMEM;
> + }
> + }
> +
> + return 0;
> +}

So here, if the perf_events allocation fails for a cpu, we free the
stuff we've already allocated [including counter_config] and return
-ENOMEM. Looking at drivers/oprofile/oprof.c:

static int __init oprofile_init(void)
{
int err;

err = oprofile_arch_init(&oprofile_ops);
if (err < 0 || timer) {
printk(KERN_INFO "oprofile: using timer interrupt.\n");
err = oprofile_timer_init(&oprofile_ops);
if (err)
goto out_arch;
}
err = oprofilefs_register();
if (err)
goto out_arch;
return 0;

out_arch:
oprofile_arch_exit();
return err;
}

So now, if timer_init fails or oprofilefs_register fails, we will
call oprofile_arch_exit, which calls oprofile_perf_exit:

> +void oprofile_perf_exit(void)
> +{
> + int id, cpu;
> +
> + for_each_possible_cpu(cpu) {
> + for (id = 0; id < perf_num_counters; ++id)
> + oprofile_destroy_counter(cpu, id);
> +
> + kfree(perf_events[cpu]);
> + }
> +
> + kfree(counter_config);
> +}

meaning that we will free everything again! This is what I
was trying to avoid in patch 1/4, by moving the counter_config
freeing into the *_exit function. Looking at it again, I think
all the freeing should be moved to the *_exit function and the init
function should just return error when allocation fails. What do you
think?

> +/*
> + * Create active perf events based on the perviously configured
> + * attributes.
> + */

typo :)

For what it's worth, I tested the series on my Cortex-A9 board and
everything seemed to work fine. I'll give the patches another spin when
we've sorted out these memory issues.

Cheers,

Will