linux-kernel - [PATCH 3/3] sched: print_rq: don't use tasklist

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Message-ID: <20140921193341.GA28628@redhat.com>
Date:	Sun, 21 Sep 2014 21:33:41 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>
Cc:	Kirill Tkhai <tkhai@...dex.ru>,
	Mike Galbraith <umgwanakikbuti@...il.com>,
	linux-kernel@...r.kernel.org
Subject: [PATCH 3/3] sched: print_rq: don't use tasklist_lock

read_lock_irqsave(tasklist_lock) in print_rq() looks strange. We do
not need to disable irqs, and they are already disabled by the caller.

And afaics this lock buys nothing, we can rely on rcu_read_lock().
In this case it makes sense to also move rcu_read_lock/unlock from
the caller to print_rq().

Signed-off-by: Oleg Nesterov <oleg@...hat.com>
---
 kernel/sched/debug.c |    7 ++-----
 1 files changed, 2 insertions(+), 5 deletions(-)

diff --git a/kernel/sched/debug.c b/kernel/sched/debug.c
index c7fe1ea..ce33780 100644
--- a/kernel/sched/debug.c
+++ b/kernel/sched/debug.c
@@ -150,7 +150,6 @@ print_task(struct seq_file *m, struct rq *rq, struct task_struct *p)
 static void print_rq(struct seq_file *m, struct rq *rq, int rq_cpu)
 {
 	struct task_struct *g, *p;
-	unsigned long flags;
 
 	SEQ_printf(m,
 	"\nrunnable tasks:\n"
@@ -159,14 +158,14 @@ static void print_rq(struct seq_file *m, struct rq *rq, int rq_cpu)
 	"------------------------------------------------------"
 	"----------------------------------------------------\n");
 
-	read_lock_irqsave(&tasklist_lock, flags);
+	rcu_read_lock();
 	for_each_process_thread(g, p) {
 		if (task_cpu(p) != rq_cpu)
 			continue;
 
 		print_task(m, rq, p);
 	}
-	read_unlock_irqrestore(&tasklist_lock, flags);
+	rcu_read_unlock();
 }
 
 void print_cfs_rq(struct seq_file *m, int cpu, struct cfs_rq *cfs_rq)
@@ -331,9 +330,7 @@ do {									\
 	print_cfs_stats(m, cpu);
 	print_rt_stats(m, cpu);
 
-	rcu_read_lock();
 	print_rq(m, rq, cpu);
-	rcu_read_unlock();
 	spin_unlock_irqrestore(&sched_debug_lock, flags);
 	SEQ_printf(m, "\n");
 }
-- 
1.5.5.1

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