linux-kernel - [PATCH v2] rcu: Dump all rcuc kthreads status for CPUs that not report quiescent state

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Date:   Tue, 19 Apr 2022 13:34:26 +0800
From:   Zqiang <qiang1.zhang@...el.com>
To:     paulmck@...nel.org, frederic@...nel.org
Cc:     rcu@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH v2] rcu: Dump all rcuc kthreads status for CPUs that not report quiescent state

If the rcutree.use_softirq is configured, when RCU Stall event
happened, dump status of all rcuc kthreads who due to starvation
prevented grace period ends on CPUs that not report quiescent
state.

Signed-off-by: Zqiang <qiang1.zhang@...el.com>
---
 v1->v2:
 rework rcuc_kthread_dump function

 kernel/rcu/tree_stall.h | 32 ++++++++++++++++++++++++++------
 1 file changed, 26 insertions(+), 6 deletions(-)

diff --git a/kernel/rcu/tree_stall.h b/kernel/rcu/tree_stall.h
index d7956c03edbd..fcf0b2e1a71c 100644
--- a/kernel/rcu/tree_stall.h
+++ b/kernel/rcu/tree_stall.h
@@ -465,11 +465,13 @@ static void print_cpu_stall_info(int cpu)
 	       falsepositive ? " (false positive?)" : "");
 }
 
-static void rcuc_kthread_dump(struct rcu_data *rdp)
+static void __rcuc_kthread_dump(int cpu)
 {
-	int cpu;
-	unsigned long j;
+	struct rcu_data *rdp;
 	struct task_struct *rcuc;
+	unsigned long j;
+
+	rdp = per_cpu_ptr(&rcu_data, cpu);
 
 	rcuc = rdp->rcu_cpu_kthread_task;
 	if (!rcuc)
@@ -488,6 +490,21 @@ static void rcuc_kthread_dump(struct rcu_data *rdp)
 		dump_cpu_task(cpu);
 }
 
+static void rcuc_kthread_dump(void)
+{
+	int cpu;
+	struct rcu_node *rnp;
+	unsigned long flags;
+
+	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))
+				__rcuc_kthread_dump(cpu);
+		raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
+	}
+}
+
 /* Complain about starvation of grace-period kthread.  */
 static void rcu_check_gp_kthread_starvation(void)
 {
@@ -597,6 +614,9 @@ static void print_other_cpu_stall(unsigned long gp_seq, unsigned long gps)
 	if (ndetected) {
 		rcu_dump_cpu_stacks();
 
+		if (!use_softirq)
+			rcuc_kthread_dump();
+
 		/* Complain about tasks blocking the grace period. */
 		rcu_for_each_leaf_node(rnp)
 			rcu_print_detail_task_stall_rnp(rnp);
@@ -659,11 +679,11 @@ static void print_cpu_stall(unsigned long gps)
 	rcu_check_gp_kthread_expired_fqs_timer();
 	rcu_check_gp_kthread_starvation();
 
-	if (!use_softirq)
-		rcuc_kthread_dump(rdp);
-
 	rcu_dump_cpu_stacks();
 
+	if (!use_softirq)
+		rcuc_kthread_dump();
+
 	raw_spin_lock_irqsave_rcu_node(rnp, flags);
 	/* Rewrite if needed in case of slow consoles. */
 	if (ULONG_CMP_GE(jiffies, READ_ONCE(rcu_state.jiffies_stall)))
-- 
2.25.1