Commit-ID: 77e38ed347162423c6b72e06c865a121081c2bb6
Gitweb: http://git.kernel.org/tip/77e38ed347162423c6b72e06c865a121081c2bb6
Author: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
AuthorDate: Sun, 25 Apr 2010 21:04:29 -0700
Committer: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
CommitDate: Mon, 10 May 2010 11:08:35 -0700
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: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
---
kernel/rcutree_plugin.h | 12 ++++++++++--
1 files changed, 10 insertions(+), 2 deletions(-)
diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h
index 0ae2339..9b18227 100644
--- a/kernel/rcutree_plugin.h
+++ b/kernel/rcutree_plugin.h
@@ -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) {
--
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