Messages in this thread | | | Date | Wed, 30 Nov 2011 20:07:27 -0600 | From | Dimitri Sivanich <> | Subject | Re: [PATCH] specific do_timer_cpu value for nohz off mode |
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On Wed, Nov 30, 2011 at 04:16:10PM -0800, Andrew Morton wrote: > 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?
See my email concerning the panic in cpu_online().
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