[PATCH 0/1] sched/deadline: Kill task_struct->pi_top_task

[PATCH 0/1] sched/deadline: Kill task_struct->pi_top_task

[Oleg Nesterov]

Hi,

The patch looks "trivial and obviously correct" but I don't understand
this code, and perhaps ->pi_top_task will have more users... Please
review.

Oleg.

[PATCH 1/1] sched/deadline: Kill task_struct->pi_top_task

[Oleg Nesterov]

Remove task_struct->pi_top_task. The only user, rt_mutex_setprio(),
can use a local.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
---
 include/linux/sched.h |    2 --
 kernel/fork.c         |    1 -
 kernel/sched/core.c   |    6 +++---
 3 files changed, 3 insertions(+), 6 deletions(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 82fe3da..2b426ee 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1386,8 +1386,6 @@ struct task_struct {
 	struct rb_node *pi_waiters_leftmost;
 	/* Deadlock detection and priority inheritance handling */
 	struct rt_mutex_waiter *pi_blocked_on;
-	/* Top pi_waiters task */
-	struct task_struct *pi_top_task;
 #endif
 
 #ifdef CONFIG_DEBUG_MUTEXES
diff --git a/kernel/fork.c b/kernel/fork.c
index 65736ca..cafea61 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1094,7 +1094,6 @@ static void rt_mutex_init_task(struct task_struct *p)
 	p->pi_waiters = RB_ROOT;
 	p->pi_waiters_leftmost = NULL;
 	p->pi_blocked_on = NULL;
-	p->pi_top_task = NULL;
 #endif
 }
 
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 268a45e..9dc8517 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2888,7 +2888,6 @@ void rt_mutex_setprio(struct task_struct *p, int prio)
 	}
 
 	trace_sched_pi_setprio(p, prio);
-	p->pi_top_task = rt_mutex_get_top_task(p);
 	oldprio = p->prio;
 	prev_class = p->sched_class;
 	on_rq = p->on_rq;
@@ -2908,8 +2907,9 @@ void rt_mutex_setprio(struct task_struct *p, int prio)
 	 *          running task
 	 */
 	if (dl_prio(prio)) {
-		if (!dl_prio(p->normal_prio) || (p->pi_top_task &&
-			dl_entity_preempt(&p->pi_top_task->dl, &p->dl))) {
+		struct task_struct *pi_task = rt_mutex_get_top_task(p);
+		if (!dl_prio(p->normal_prio) ||
+		    (pi_task && dl_entity_preempt(&pi_task->dl, &p->dl))) {
 			p->dl.dl_boosted = 1;
 			p->dl.dl_throttled = 0;
 			enqueue_flag = ENQUEUE_REPLENISH;
-- 
1.5.5.1

[tip:sched/core] sched/deadline: Kill task_struct->pi_top_task

[tip-bot for Oleg Nesterov]

Commit-ID:  466af29bf4270e84261712428a1304c28e3743fa
Gitweb:     http://git.kernel.org/tip/466af29bf4270e84261712428a1304c28e3743fa
Author:     Oleg Nesterov <oleg@redhat.com>
AuthorDate: Fri, 6 Jun 2014 18:52:06 +0200
Committer:  Ingo Molnar <mingo@kernel.org>
CommitDate: Wed, 16 Jul 2014 13:38:18 +0200

sched/deadline: Kill task_struct->pi_top_task

Remove task_struct->pi_top_task. The only user, rt_mutex_setprio(),
can use a local.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Cc: Juri Lelli <juri.lelli@gmail.com>
Cc: Alex Thorlton <athorlton@sgi.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Daeseok Youn <daeseok.youn@gmail.com>
Cc: Dario Faggioli <raistlin@linux.it>
Cc: Davidlohr Bueso <davidlohr@hp.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Eric W. Biederman <ebiederm@xmission.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Matthew Dempsky <mdempsky@chromium.org>
Cc: Michal Simek <michal.simek@xilinx.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Link: http://lkml.kernel.org/r/20140606165206.GB29465@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 include/linux/sched.h | 2 --
 kernel/fork.c         | 1 -
 kernel/sched/core.c   | 6 +++---
 3 files changed, 3 insertions(+), 6 deletions(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 306f4f0..c9c9ff7 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1440,8 +1440,6 @@ struct task_struct {
 	struct rb_node *pi_waiters_leftmost;
 	/* Deadlock detection and priority inheritance handling */
 	struct rt_mutex_waiter *pi_blocked_on;
-	/* Top pi_waiters task */
-	struct task_struct *pi_top_task;
 #endif
 
 #ifdef CONFIG_DEBUG_MUTEXES
diff --git a/kernel/fork.c b/kernel/fork.c
index d2799d1..6ff87f442 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1095,7 +1095,6 @@ static void rt_mutex_init_task(struct task_struct *p)
 	p->pi_waiters = RB_ROOT;
 	p->pi_waiters_leftmost = NULL;
 	p->pi_blocked_on = NULL;
-	p->pi_top_task = NULL;
 #endif
 }
 
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 2dbc63d..cf7695a 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2980,7 +2980,6 @@ void rt_mutex_setprio(struct task_struct *p, int prio)
 	}
 
 	trace_sched_pi_setprio(p, prio);
-	p->pi_top_task = rt_mutex_get_top_task(p);
 	oldprio = p->prio;
 	prev_class = p->sched_class;
 	on_rq = p->on_rq;
@@ -3000,8 +2999,9 @@ void rt_mutex_setprio(struct task_struct *p, int prio)
 	 *          running task
 	 */
 	if (dl_prio(prio)) {
-		if (!dl_prio(p->normal_prio) || (p->pi_top_task &&
-			dl_entity_preempt(&p->pi_top_task->dl, &p->dl))) {
+		struct task_struct *pi_task = rt_mutex_get_top_task(p);
+		if (!dl_prio(p->normal_prio) ||
+		    (pi_task && dl_entity_preempt(&pi_task->dl, &p->dl))) {
 			p->dl.dl_boosted = 1;
 			p->dl.dl_throttled = 0;
 			enqueue_flag = ENQUEUE_REPLENISH;