rcu: Check the return value of zalloc_cpumask_var()

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@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Tested-by: Paul Gortmaker <paul.gortmaker@windriver.com>

kernel/rcu/tree_plugin.h

@@ -2440,7 +2440,10 @@ void __init rcu_init_nohz(void)
 #endif /* #if defined(CONFIG_NO_HZ_FULL) */
 
 	if (!have_rcu_nocb_mask && need_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, callback offloading disabled.\n");
+			return;
+		}
 		have_rcu_nocb_mask = true;
 	}
 	if (!have_rcu_nocb_mask)