[07/10] sched/debug: Try trigger_single_cpu_backtrace(cpu) in dump_cpu_task()

Commit Message

Paul E. McKenney Aug. 31, 2022, 6:08 p.m. UTC

From: Zhen Lei <[e-mail]>

The trigger_all_cpu_backtrace() function attempts to send an NMI to the
target CPU, which usually provides much better stack traces than the
dump_cpu_task() function's approach of dumping that stack from some other
CPU.  So much so that most calls to dump_cpu_task() only happen after
a call to trigger_all_cpu_backtrace() has failed.  And the exception to
this rule really should attempt to use trigger_all_cpu_backtrace() first.

Therefore, move the trigger_all_cpu_backtrace() invocation into
dump_cpu_task().

Signed-off-by: Zhen Lei <[e-mail]>
Signed-off-by: Paul E. McKenney <[e-mail]>
Cc: Ingo Molnar <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
Cc: Juri Lelli <[e-mail]>
Cc: Vincent Guittot <[e-mail]>
Cc: Dietmar Eggemann <[e-mail]>
Cc: Ben Segall <[e-mail]>
Cc: Mel Gorman <[e-mail]>
Cc: Daniel Bristot de Oliveira <[e-mail]>
Cc: Valentin Schneider <[e-mail]>
---
 kernel/rcu/tree_stall.h | 5 ++---
 kernel/sched/core.c     | 3 +++
 kernel/smp.c            | 3 +--
 3 files changed, 6 insertions(+), 5 deletions(-)

Patch

diff --git a/kernel/rcu/tree_stall.h b/kernel/rcu/tree_stall.h
index c3fbbcc09327f..5653560573e22 100644
--- a/kernel/rcu/tree_stall.h
+++ b/kernel/rcu/tree_stall.h
@@ -368,7 +368,7 @@  static void rcu_dump_cpu_stacks(void)
 			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))
+				else
 					dump_cpu_task(cpu);
 			}
 		raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
@@ -511,8 +511,7 @@  static void rcu_check_gp_kthread_starvation(void)
 					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);
+					dump_cpu_task(cpu);
 				}
 			}
 			wake_up_process(gpk);
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index ee28253c9ac0c..e15b6a7f34f47 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -11183,6 +11183,9 @@  struct cgroup_subsys cpu_cgrp_subsys = {
 
 void dump_cpu_task(int cpu)
 {
+	if (trigger_single_cpu_backtrace(cpu))
+		return;
+
 	pr_info("Task dump for CPU %d:\n", cpu);
 	sched_show_task(cpu_curr(cpu));
 }
diff --git a/kernel/smp.c b/kernel/smp.c
index 650810a6f29b3..e8cdc025a046f 100644
--- a/kernel/smp.c
+++ b/kernel/smp.c
@@ -370,8 +370,7 @@  static bool csd_lock_wait_toolong(struct __call_single_data *csd, u64 ts0, u64 *
 	if (cpu >= 0) {
 		if (static_branch_unlikely(&csdlock_debug_extended))
 			csd_lock_print_extended(csd, cpu);
-		if (!trigger_single_cpu_backtrace(cpu))
-			dump_cpu_task(cpu);
+		dump_cpu_task(cpu);
 		if (!cpu_cur_csd) {
 			pr_alert("csd: Re-sending CSD lock (#%d) IPI from CPU#%02d to CPU#%02d\n", *bug_id, raw_smp_processor_id(), cpu);
 			arch_send_call_function_single_ipi(cpu);