linux-kernel - Re: [PATCH v4 04/22] kthread: Add create_kthread

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Date:	Tue, 16 Feb 2016 16:44:43 +0100
From:	Petr Mladek <pmladek@...e.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Oleg Nesterov <oleg@...hat.com>,
	Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Josh Triplett <josh@...htriplett.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Jiri Kosina <jkosina@...e.cz>, Borislav Petkov <bp@...e.de>,
	Michal Hocko <mhocko@...e.cz>, linux-mm@...ck.org,
	Vlastimil Babka <vbabka@...e.cz>, linux-api@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 04/22] kthread: Add create_kthread_worker*()

On Mon 2016-01-25 13:53:39, Tejun Heo wrote:
> On Mon, Jan 25, 2016 at 04:44:53PM +0100, Petr Mladek wrote:
> > +struct kthread_worker *
> > +create_kthread_worker_on_cpu(int cpu, const char namefmt[])
> > +{
> > +	if (cpu < 0 || cpu > num_possible_cpus())
> > +		return ERR_PTR(-EINVAL);
> 
> Comparing cpu ID to num_possible_cpus() doesn't make any sense.  It
> should either be testing against cpu_possible_mask or testing against
> nr_cpu_ids.  Does this test need to be in this function at all?

I wanted to be sure. The cpu number is later passed to
cpu_to_node(cpu) in kthread_create_on_cpu().

I am going to replace this with a check against nr_cpu_ids in
kthread_create_on_cpu() which makes more sense.

I might be too paranoid. But this is slow path. People
do mistakes...

Thanks,
Petr