linux-kernel - Re: [PATCH v2 2/2] rcu: Check the return value of rcu_nocb

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Message-ID: <20140725152551.GC11241@linux.vnet.ibm.com>
Date:	Fri, 25 Jul 2014 08:25:51 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Pranith Kumar <bobby.prani@...il.com>
Cc:	Josh Triplett <josh@...htriplett.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Lai Jiangshan <laijs@...fujitsu.com>,
	"open list:READ-COPY UPDATE..." <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 2/2] rcu: Check the return value of rcu_nocb_mask
 cpumask allocation

On Thu, Jul 24, 2014 at 08:37:32PM -0400, Pranith Kumar wrote:
> This commit checks the return value of the zalloc_cpumask_var() used for
> allocating cpumask for rcu_nocb_mask.
> 
> Signed-off-by: Pranith Kumar <bobby.prani@...il.com>

Hmmm...  I saw the check in the previous patch, but didn't see removal
of the later have_rcu_nocb_mask check.  Please see below.

							Thanx, Paul

> ---
> v2: no change from v1
> 
>  kernel/rcu/tree_plugin.h | 23 ++++++++++++-----------
>  1 file changed, 12 insertions(+), 11 deletions(-)
> 
> diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
> index 520538a..9c9a01c 100644
> --- a/kernel/rcu/tree_plugin.h
> +++ b/kernel/rcu/tree_plugin.h
> @@ -54,7 +54,10 @@ static void __init rcu_bootup_announce_oddness_nocb(void)
>  {
>  #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;
> +		}
>  		have_rcu_nocb_mask = true;
>  	}
>  #ifdef CONFIG_RCU_NOCB_CPU_ZERO
> @@ -66,17 +69,15 @@ static void __init rcu_bootup_announce_oddness_nocb(void)
>  	cpumask_copy(rcu_nocb_mask, cpu_possible_mask);
>  #endif /* #ifdef CONFIG_RCU_NOCB_CPU_ALL */
>  #endif /* #ifndef CONFIG_RCU_NOCB_CPU_NONE */
> -	if (have_rcu_nocb_mask) {
> -		if (!cpumask_subset(rcu_nocb_mask, cpu_possible_mask)) {
> -			pr_info("\tNote: kernel parameter 'rcu_nocbs=' contains nonexistent CPUs.\n");
> -			cpumask_and(rcu_nocb_mask, cpu_possible_mask,
> -				    rcu_nocb_mask);
> -		}
> -		cpulist_scnprintf(nocb_buf, sizeof(nocb_buf), rcu_nocb_mask);
> -		pr_info("\tOffload RCU callbacks from CPUs: %s.\n", nocb_buf);
> -		if (rcu_nocb_poll)
> -			pr_info("\tPoll for callbacks from no-CBs CPUs.\n");
> +	if (!cpumask_subset(rcu_nocb_mask, cpu_possible_mask)) {

What happens if CONFIG_RCU_NOCB_CPU_NONE=y and the rcu_nocbs= boot
parameter is not specified and we get here?

In order to get visible failures when testing, build with
CONFIG_CPUMASK_OFFSTACK=y.

> +		pr_info("\tNote: kernel parameter 'rcu_nocbs=' contains nonexistent CPUs.\n");
> +		cpumask_and(rcu_nocb_mask, cpu_possible_mask,
> +				rcu_nocb_mask);
>  	}
> +	cpulist_scnprintf(nocb_buf, sizeof(nocb_buf), rcu_nocb_mask);
> +	pr_info("\tOffload RCU callbacks from CPUs: %s.\n", nocb_buf);
> +	if (rcu_nocb_poll)
> +		pr_info("\tPoll for callbacks from no-CBs CPUs.\n");
>  }
> 
>  /*
> -- 
> 2.0.1
> 

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