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Date: Tue, 16 Feb 2016 17:10:09 +0100
From: Petr Mladek <pmladek@suse.com>
To: Tejun Heo <tj@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>, Oleg Nesterov <oleg@redhat.com>,
        Ingo Molnar <mingo@redhat.com>, Peter Zijlstra <peterz@infradead.org>,
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        Thomas Gleixner <tglx@linutronix.de>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Jiri Kosina <jkosina@suse.cz>, Borislav Petkov <bp@suse.de>,
        Michal Hocko <mhocko@suse.cz>, linux-mm@kvack.org,
        Vlastimil Babka <vbabka@suse.cz>, linux-api@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH v4 04/22] kthread: Add create_kthread_worker*()
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On Tue 2016-02-16 16:44:43, Petr Mladek wrote:
> 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...

I take it back. I will remove the check at all.
Michal Hocko persuaded me offline that it does not make
much sense. This function is used from kernel code.
I need to believe that the usage is sane at this level.
Also too many checks makes the code harder to read.

Thanks,
Petr