Commit 187497fa authored Jul 16, 2014 by Paul E. McKenney

rcu: Allow for NULL tick_nohz_full_mask when nohz_full= missing



If there isn't a nohz_full= kernel parameter specified, then
tick_nohz_full_mask can legitimately be NULL.  This can cause
problems when RCU's boot code tries to cpumask_or() this value into
rcu_nocb_mask.  In addition, if NO_HZ_FULL_ALL=y, there is no point
in doing the cpumask_or() in the first place because this will cause
RCU_NOCB_CPU_ALL=y, which in turn will have all bits already set in
rcu_nocb_mask.

This commit therefore avoids the cpumask_or() if NO_HZ_FULL_ALL=y
and checks for !tick_nohz_full_running otherwise, this latter check
catching cases when there was no nohz_full= kernel parameter specified.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

parent 1823172a

kernel/rcu/tree_plugin.h

+4 −3

Original line number	Diff line number	Diff line
		@@ -2479,9 +2479,10 @@ static void __init rcu_spawn_nocb_kthreads(struct rcu_state *rsp)

		if (rcu_nocb_mask == NULL)
		return;
		#ifdef CONFIG_NO_HZ_FULL
		#if defined(CONFIG_NO_HZ_FULL) && !defined(CONFIG_NO_HZ_FULL_ALL)
		if (tick_nohz_full_running)
		cpumask_or(rcu_nocb_mask, rcu_nocb_mask, tick_nohz_full_mask);
		#endif /* #ifdef CONFIG_NO_HZ_FULL */
		#endif /* #if defined(CONFIG_NO_HZ_FULL) && !defined(CONFIG_NO_HZ_FULL_ALL) */
		if (ls == -1) {
		ls = int_sqrt(nr_cpu_ids);
		rcu_nocb_leader_stride = ls;

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