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>
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@ -1051,6 +1051,8 @@ static DEFINE_PER_CPU(unsigned long, rcu_dyntick_holdoff);
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int rcu_needs_cpu(int cpu)
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{
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int c = 0;
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int snap;
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int snap_nmi;
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int thatcpu;
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/* Check for being in the holdoff period. */
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@ -1058,12 +1060,18 @@ int rcu_needs_cpu(int cpu)
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return rcu_needs_cpu_quick_check(cpu);
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/* Don't bother unless we are the last non-dyntick-idle CPU. */
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for_each_cpu_not(thatcpu, nohz_cpu_mask)
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if (cpu_online(thatcpu) && thatcpu != cpu) {
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for_each_online_cpu(thatcpu) {
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if (thatcpu == cpu)
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continue;
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snap = per_cpu(rcu_dynticks, thatcpu)->dynticks;
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snap_nmi = per_cpu(rcu_dynticks, thatcpu)->dynticks_nmi;
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smp_mb(); /* Order sampling of snap with end of grace period. */
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if (((snap & 0x1) != 0) || ((snap_nmi & 0x1) != 0)) {
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per_cpu(rcu_dyntick_drain, cpu) = 0;
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per_cpu(rcu_dyntick_holdoff, cpu) = jiffies - 1;
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return rcu_needs_cpu_quick_check(cpu);
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}
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}
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/* Check and update the rcu_dyntick_drain sequencing. */
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if (per_cpu(rcu_dyntick_drain, cpu) <= 0) {
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