[PATCH tip/core/rcu 3/4] rcu: Do not NMI offline CPUs

paulmck
2021-01-06T16:53:42Z

Currently, RCU CPU stall warning messages will NMI whatever CPU looks
like it is blocking either the current grace period or the grace-period
kthread. This can produce confusing output if the target CPU is offline.
This commit therefore checks for offline CPUs.

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
kernel/rcu/tree_stall.h | 17 ++++++++++++-----
1 file changed, 12 insertions(+), 5 deletions(-)

diff --git a/kernel/rcu/tree_stall.h b/kernel/rcu/tree_stall.h
index 35c1355..29cf096 100644
--- a/kernel/rcu/tree_stall.h
+++ b/kernel/rcu/tree_stall.h
@@ -333,9 +333,12 @@ static void rcu_dump_cpu_stacks(void)
rcu_for_each_leaf_node(rnp) {
raw_spin_lock_irqsave_rcu_node(rnp, flags);
for_each_leaf_node_possible_cpu(rnp, cpu)
- if (rnp->qsmask & leaf_node_cpu_bit(rnp, cpu))
- if (!trigger_single_cpu_backtrace(cpu))
+ if (rnp->qsmask & leaf_node_cpu_bit(rnp, cpu)) {
+ if (cpu_is_offline(cpu))
+ pr_err("Offline CPU %d blocking current GP.\n", cpu);
+ else if (!trigger_single_cpu_backtrace(cpu))
dump_cpu_task(cpu);
+ }
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
}
}
@@ -466,9 +469,13 @@ static void rcu_check_gp_kthread_starvation(void)
pr_err("RCU grace-period kthread stack dump:\n");
sched_show_task(gpk);
if (cpu >= 0) {
- pr_err("Stack dump where RCU grace-period kthread last ran:\n");
- if (!trigger_single_cpu_backtrace(cpu))
- dump_cpu_task(cpu);
+ if (cpu_is_offline(cpu)) {
+ pr_err("RCU GP kthread last ran on offline CPU %d.\n", cpu);
+ } else {
+ pr_err("Stack dump where RCU GP kthread last ran:\n");
+ if (!trigger_single_cpu_backtrace(cpu))
+ dump_cpu_task(cpu);
+ }
}
wake_up_process(gpk);
}
--
2.9.5