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Date:	Thu, 17 Jul 2014 17:30:11 -0400
From:	Pranith Kumar <>
To:	"Paul E. McKenney" <>,
	Josh Triplett <>,
	Steven Rostedt <>,
	Mathieu Desnoyers <>,
	Lai Jiangshan <>, (open list:READ-COPY UPDATE...)
Subject: [PATCH 1/1] rcu: Check for have_rcu_nocb_mask instead of rcu_nocb_mask

Hi Paul,

This is something similar to what you found yesterday with tick_nohz_full mask.


If we configure a kernel with CONFIG_NOCB_CPU=y, CONFIG_RCU_NOCB_CPU_NONE=y and
CONFIG_CPUMASK_OFFSTACK=n and do not pass in a rcu_nocb= boot parameter, the
cpumask rcu_nocb_mask can be garbage instead of NULL.

Hence this commit replaces checks for rcu_nocb_mask == NULL with a check for

Signed-off-by: Pranith Kumar <>
 kernel/rcu/tree_plugin.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index cedb020..15c00b5 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -2542,7 +2542,7 @@ static void __init rcu_organize_nocb_kthreads(struct rcu_state *rsp)
 	struct rcu_data *rdp_leader = NULL;  /* Suppress misguided gcc warn. */
 	struct rcu_data *rdp_prev = NULL;
-	if (rcu_nocb_mask == NULL)
+	if (!have_rcu_nocb_mask)
 	cpumask_or(rcu_nocb_mask, rcu_nocb_mask, tick_nohz_full_mask);
@@ -2575,7 +2575,7 @@ static void __init rcu_organize_nocb_kthreads(struct rcu_state *rsp)
 /* Prevent __call_rcu() from enqueuing callbacks on no-CBs CPUs */
 static bool init_nocb_callback_list(struct rcu_data *rdp)
-	if (rcu_nocb_mask == NULL ||
+	if (have_rcu_nocb_mask == false ||
 	    !cpumask_test_cpu(rdp->cpu, rcu_nocb_mask))
 		return false;
 	rdp->nxttail[RCU_NEXT_TAIL] = NULL;

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