Messages in this thread | | | Date | Wed, 30 Nov 2011 16:16:10 -0800 | From | Andrew Morton <> | Subject | Re: [PATCH] specific do_timer_cpu value for nohz off mode |
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On Wed, 30 Nov 2011 16:11:31 -0800 Andrew Morton <akpm@linux-foundation.org> wrote:
> On Wed, 30 Nov 2011 09:29:59 -0600 > Dimitri Sivanich <sivanich@sgi.com> wrote: > > > +static ssize_t sysfs_store_do_timer_cpu(struct sys_device *dev, > > + struct sysdev_attribute *attr, > > + const char *buf, size_t size) > > +{ > > + struct sysdev_ext_attribute *ea = SYSDEV_TO_EXT_ATTR(attr); > > + unsigned int new; > > + int rv; > > + > > +#ifdef CONFIG_NO_HZ > > + /* nohz mode not supported */ > > + if (tick_nohz_enabled) > > + return -EINVAL; > > +#endif > > + > > + rv = kstrtouint(buf, 0, &new); > > + if (rv) > > + return rv; > > + > > + if (new >= NR_CPUS || !cpu_online(new)) > > + return -ERANGE; > > + > > + *(unsigned int *)(ea->var) = new; > > + return size; > > +} > > checkpatch tells us: > > WARNING: usage of NR_CPUS is often wrong - consider using cpu_possible(), num_possible_cpus(), for_each_possible_cpu(), etc > > I think the check can just be removed? Surely cpu_online(1000000000) > will return false? >
And the whole thing is racy, isn't it? The "new" CPU can go offline a nanosecond after we performed that test, so why perform it at all?
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