[PATCH] rcu-tasks: Dump rtpcp->lazy_timer status in show_rcu_tasks_generic_gp_kthread()

[PATCH] rcu-tasks: Dump rtpcp->lazy_timer status in show_rcu_tasks_generic_gp_kthread()

[Zqiang]

Add 'P' flag to the diagnostic line to indicate whether any per-cpu
rtpcp's lazy_timer is pending.  this helps diagnose stalls where
rcu-task callbacks are queued but the kthread stay sleep because
the lazy_timer has not yet fired and no grace period has started.

The output is as follows:

[   31.319540][   T77] call_rcu_tasks() has failed boot-time tests.
[   31.320205][   T77] rcu_tasks: RTGS_WAIT_CBS(11) since 7518 g:4 i:0 kCuUP l:150000

Signed-off-by: Zqiang <qiang.zhang@linux.dev>
---
 kernel/rcu/tasks.h | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h
index 6720dc25cd39..a146d1d98c22 100644
--- a/kernel/rcu/tasks.h
+++ b/kernel/rcu/tasks.h
@@ -723,6 +723,7 @@ static void show_rcu_tasks_generic_gp_kthread(struct rcu_tasks *rtp, char *s)
 	bool havecbs = false;
 	bool haveurgent = false;
 	bool haveurgentcbs = false;
+	bool havependtimer = false;
 
 	for_each_possible_cpu(cpu) {
 		struct rcu_tasks_percpu *rtpcp = per_cpu_ptr(rtp->rtpcpu, cpu);
@@ -733,10 +734,12 @@ static void show_rcu_tasks_generic_gp_kthread(struct rcu_tasks *rtp, char *s)
 			haveurgent = true;
 		if (!data_race(rcu_segcblist_empty(&rtpcp->cblist)) && data_race(rtpcp->urgent_gp))
 			haveurgentcbs = true;
-		if (havecbs && haveurgent && haveurgentcbs)
+		if (data_race(timer_pending(&rtpcp->lazy_timer)))
+			havependtimer = true;
+		if (havecbs && haveurgent && haveurgentcbs && havependtimer)
 			break;
 	}
-	pr_info("%s: %s(%d) since %lu g:%lu i:%lu %c%c%c%c l:%lu %s\n",
+	pr_info("%s: %s(%d) since %lu g:%lu i:%lu %c%c%c%c%c l:%lu %s\n",
 		rtp->kname,
 		tasks_gp_state_getname(rtp), data_race(rtp->gp_state),
 		jiffies - data_race(rtp->gp_jiffies),
@@ -746,6 +749,7 @@ static void show_rcu_tasks_generic_gp_kthread(struct rcu_tasks *rtp, char *s)
 		".C"[havecbs],
 		".u"[haveurgent],
 		".U"[haveurgentcbs],
+		".P"[havependtimer],
 		rtp->lazy_jiffies,
 		s);
 }
-- 
2.17.1