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Commit 77e38ed3 authored by Paul E. McKenney's avatar Paul E. McKenney
Browse files

rcu: RCU_FAST_NO_HZ must check RCU dyntick state 



The current version of RCU_FAST_NO_HZ reproduces the old CLASSIC_RCU
dyntick-idle bug, as it fails to detect CPUs that have interrupted
or NMIed out of dyntick-idle mode.  Fix this by making rcu_needs_cpu()
check the state in the per-CPU rcu_dynticks variables, thus correctly
detecting the dyntick-idle state from an RCU perspective.

Signed-off-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
parent d14aada8

kernel/rcutree_plugin.h

+10 −2
Original line number Diff line number Diff line
@@ -1051,6 +1051,8 @@ static DEFINE_PER_CPU(unsigned long, rcu_dyntick_holdoff); 
int rcu_needs_cpu(int cpu)

{

	int c = 0;

	int snap;

	int snap_nmi;

	int thatcpu;



	/* Check for being in the holdoff period. */
@@ -1058,12 +1060,18 @@ int rcu_needs_cpu(int cpu) 
		return rcu_needs_cpu_quick_check(cpu);



	/* Don't bother unless we are the last non-dyntick-idle CPU. */

	for_each_cpu_not(thatcpu, nohz_cpu_mask)

		if (cpu_online(thatcpu) && thatcpu != cpu) {

	for_each_online_cpu(thatcpu) {

		if (thatcpu == cpu)

			continue;

		snap = per_cpu(rcu_dynticks, thatcpu)->dynticks;

		snap_nmi = per_cpu(rcu_dynticks, thatcpu)->dynticks_nmi;

		smp_mb(); /* Order sampling of snap with end of grace period. */

		if (((snap & 0x1) != 0) || ((snap_nmi & 0x1) != 0)) {

			per_cpu(rcu_dyntick_drain, cpu) = 0;

			per_cpu(rcu_dyntick_holdoff, cpu) = jiffies - 1;

			return rcu_needs_cpu_quick_check(cpu);

		}

	}



	/* Check and update the rcu_dyntick_drain sequencing. */

	if (per_cpu(rcu_dyntick_drain, cpu) <= 0) {