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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@linux.vnet.ibm.com>
This commit is contained in:
Paul E. McKenney 2010-04-25 21:04:29 -07:00
parent d14aada8e2
commit 77e38ed347
1 changed files with 10 additions and 2 deletions
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12
kernel/rcutree_plugin.h
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@ -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) {