[PATCH] sched/debug: avoid executing show_state and causing rcu stall warning

From: Liu Song <liusong@linux.alibaba.com>
To: mingo@redhat.com, peterz@infradead.org, juri.lelli@redhat.com,
	vincent.guittot@linaro.org, dietmar.eggemann@arm.com,
	rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de,
	bristot@redhat.com, vschneid@redhat.com
Cc: linux-kernel@vger.kernel.org
Subject: [PATCH] sched/debug: avoid executing show_state and causing rcu stall warning
Date: Wed,  3 Aug 2022 09:18:45 +0800	[thread overview]
Message-ID: <1659489525-82994-1-git-send-email-liusong@linux.alibaba.com> (raw)

From: Liu Song <liusong@linux.alibaba.com>

If the number of CPUs is large, "sysrq_sched_debug_show" will execute for
a long time. Every time I execute "echo t > /proc/sysrq-trigger" on my
128-core machine, the rcu stall warning will be triggered. Moreover,
sysrq_sched_debug_show does not need to be protected by rcu_read_lock,
and no rcu stall warning will appear after adjustment.

Signed-off-by: Liu Song <liusong@linux.alibaba.com>
---
 kernel/sched/core.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 5555e49..82c117e 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -8879,11 +8879,11 @@ void show_state_filter(unsigned int state_filter)
 			sched_show_task(p);
 	}
 
+	rcu_read_unlock();
 #ifdef CONFIG_SCHED_DEBUG
 	if (!state_filter)
 		sysrq_sched_debug_show();
 #endif
-	rcu_read_unlock();
 	/*
 	 * Only show locks if all tasks are dumped:
 	 */
-- 
1.8.3.1

