Re: [PATCH 02/16] rcu: Check return value for cpumask allocation

Pranith Kumar
2014-07-23T17:14:52Z

On Wed, Jul 23, 2014 at 8:06 AM, Paul E. McKenney
<paulmck@linux.vnet.ibm.com> wrote:
>> --- a/kernel/rcu/tree_plugin.h
>> +++ b/kernel/rcu/tree_plugin.h
>> @@ -88,7 +88,10 @@ static void __init rcu_bootup_announce_oddness(void)
>> #ifdef CONFIG_RCU_NOCB_CPU
>> #ifndef CONFIG_RCU_NOCB_CPU_NONE
>> if (!have_rcu_nocb_mask) {
>> - zalloc_cpumask_var(&rcu_nocb_mask, GFP_KERNEL);
>> + if (!zalloc_cpumask_var(&rcu_nocb_mask, GFP_KERNEL)) {
>> + pr_info("rcu_nocb_mask allocation failed\n");
>> + return;
>
> Good catch, but this "return" is an accident waiting to happen. The
> accident will happen as soon as another RCU option appears, and the
> person adding it quite naturally adds it at the end of this function.
> The cleanest approach is to make an rcu_bootup_announce_oddness_nocb()
> as one commit that does -only- code motion, and the make this change
> as another commit.
>

Hi Paul,

Looking at this, I think the following is simpler without having to
introduce a new function. What do you think?

diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index c31eb28..f2ed342 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -88,8 +88,10 @@ static void __init rcu_bootup_announce_oddness(void)
#ifdef CONFIG_RCU_NOCB_CPU
#ifndef CONFIG_RCU_NOCB_CPU_NONE
if (!have_rcu_nocb_mask) {
- zalloc_cpumask_var(&rcu_nocb_mask, GFP_KERNEL);
- have_rcu_nocb_mask = true;
+ if (!zalloc_cpumask_var(&rcu_nocb_mask, GFP_KERNEL))
+ pr_info("rcu_nocb_mask allocation failed");
+ else
+ have_rcu_nocb_mask = true;
}
#ifdef CONFIG_RCU_NOCB_CPU_ZERO
pr_info("\tOffload RCU callbacks from CPU 0\n");

--
Pranith