Re: [PATCH 5/6] workqueue: introduce NR_WORKER_POOLS and for_each_worker_pool()

Linus Torvalds
2012-07-14T04:27:27Z

Seeing code like this

+ return &(*nr_running)[0];

just makes me go "WTF?"

Why are you taking the address of something you just dereferenced (the
"& [0]" part).

And you actually do that *twice*, except the inner one is more
complicated. When you assign nr_runing, you take the address of it, so
the "*nr_running" is actually just the same kind of odd thing (except
in reverse - you take dereference something you just took the
address-of).

Seriously, this to me is a sign of *deeply* confused code. And the
fact that your first version of that code was buggy *EXACTLY* due to
this confusion should have made you take a step back.

As far as I can tell, what you actually want that function to do is:

static atomic_t *get_pool_nr_running(struct worker_pool *pool)
{
int cpu = pool->gcwq->cpu;

if (cpu != WORK_CPU_UNBOUND)
return per_cpu(pool_nr_running, cpu);

return unbound_pool_nr_running;
}

Notice how there isn't an 'address-of' operator anywhere in sight
there. Those things are arrays, they get turned into "atomic_t *"
automatically. And there isn't a single dereference (not a '*', and
not a "[0]" - they are the exact same thing, btw) in sight either.

What am I missing? Are there some new drugs that all the cool kids
chew that I should be trying? Because I really don't think the kinds
of insane "take the address of a dereference" games are a good idea.
They really look to me like somebody is having a really bad drug
experience.

I didn't test the code, btw. I just looked at the patch and went WTF.

Linus