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 a 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@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Kirill Tkhai <tkhai@yandex.ru>
Cc: Mike Galbraith <umgwanakikbuti@gmail.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/20140921193338.GA28621@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 6 insertions, 10 deletions

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 0abfb7ec9e62..d65566d07fcf 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -7220,12 +7220,12 @@ 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;
@@ -7240,20 +7240,16 @@ 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 */