linux-kernel - [PATCH 1/2] sched: normalize_rt_tasks: don't use _irqsave for tasklist_lock, use task_rq

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Date:	Sun, 17 Aug 2014 17:26:16 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Rik van Riel <riel@...hat.com>,
	Mike Galbraith <umgwanakikbuti@...il.com>,
	Hidetoshi Seto <seto.hidetoshi@...fujitsu.com>,
	Frank Mayhar <fmayhar@...gle.com>,
	Frederic Weisbecker <fweisbec@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Sanjay Rao <srao@...hat.com>,
	Larry Woodman <lwoodman@...hat.com>,
	linux-kernel@...r.kernel.org, Kirill Tkhai <tkhai@...dex.ru>
Subject: [PATCH 1/2] sched: normalize_rt_tasks: don't use _irqsave for
	tasklist_lock, use task_rq_lock()

1. read_lock(tasklist_lock) does not need to disable irqs.

2. ->mm != NULL is the common mistake, use PF_KTHREAD.

3. The second ->mm check can be simply removed.

4. task_rq_lock() looks better than raw_spin_lock(&p->pi_lock) +
   __task_rq_lock().

Signed-off-by: Oleg Nesterov <oleg@...hat.com>
---
 kernel/sched/core.c |   16 ++++++----------
 1 files changed, 6 insertions(+), 10 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 8a6506f..eee12b3 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -7137,12 +7137,12 @@ void normalize_rt_tasks(void)
 	unsigned long flags;
 	struct rq *rq;
 
-	read_lock_irqsave(&tasklist_lock, flags);
+	read_lock(&tasklist_lock);
 	for_each_process_thread(g, p) {
 		/*
 		 * Only normalize user tasks:
 		 */
-		if (!p->mm)
+		if (p->flags & PF_KTHREAD)
 			continue;
 
 		p->se.exec_start		= 0;
@@ -7157,20 +7157,16 @@ void normalize_rt_tasks(void)
 			 * Renice negative nice level userspace
 			 * tasks back to 0:
 			 */
-			if (task_nice(p) < 0 && p->mm)
+			if (task_nice(p) < 0)
 				set_user_nice(p, 0);
 			continue;
 		}
 
-		raw_spin_lock(&p->pi_lock);
-		rq = __task_rq_lock(p);
-
+		rq = task_rq_lock(p, &flags);
 		normalize_task(rq, p);
-
-		__task_rq_unlock(rq);
-		raw_spin_unlock(&p->pi_lock);
+		task_rq_unlock(rq, p, &flags);
 	}
-	read_unlock_irqrestore(&tasklist_lock, flags);
+	read_unlock(&tasklist_lock);
 }
 
 #endif /* CONFIG_MAGIC_SYSRQ */
-- 
1.5.5.1


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