[PATCH 0/3] sched: fix tg_has_rt_tasks(), tasklist_lock cleanups

[PATCH 0/3] sched: fix tg_has_rt_tasks(), tasklist_lock cleanups

[Oleg Nesterov]

This textually depends on

	5d07f4202c5d63b73ba1734ed38e08461a689313
	"sched: s/do_each_thread/for_each_process_thread/ in core.c"

	d38e83c715270cc2e137bbf6f25206c8c023896b
	"sched: s/do_each_thread/for_each_process_thread/ in debug.c"

in -tip tree.

Kirill, you seem to agree with 1/3, I'll appreciate your ack.

Oleg.

[PATCH 1/3] sched: fix the task-group check in tg_has_rt_tasks()

[Oleg Nesterov]

tg_has_rt_tasks() wants to find an RT task in this task_group, but
task_rq(p)->rt.tg wrongly checks the root rt_rq.

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

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index eee12b3..9023f56 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -7354,7 +7354,7 @@ static inline int tg_has_rt_tasks(struct task_group *tg)
 	struct task_struct *g, *p;
 
 	for_each_process_thread(g, p) {
-		if (rt_task(p) && task_rq(p)->rt.tg == tg)
+		if (rt_task(p) && task_group(p) == tg)
 			return 1;
 	}
 
-- 
1.5.5.1

[PATCH 2/3] sched: normalize_rt_tasks: don't use _irqsave for tasklist_lock, use task_rq_lock()

[Oleg Nesterov]

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@redhat.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

[PATCH 3/3] sched: print_rq: don't use tasklist_lock

[Oleg Nesterov]

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@redhat.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

Re: [PATCH 1/3] sched: fix the task-group check in tg_has_rt_tasks()

[Kirill Tkhai]

В Вс, 21/09/2014 в 21:33 +0200, Oleg Nesterov пишет:
> tg_has_rt_tasks() wants to find an RT task in this task_group, but
> task_rq(p)->rt.tg wrongly checks the root rt_rq.
> 
> Signed-off-by: Oleg Nesterov <oleg@redhat.com>

Reviewed-by: Kirill Tkhai <ktkhai@parallels.com>

> ---
>  kernel/sched/core.c |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
> 
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index eee12b3..9023f56 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -7354,7 +7354,7 @@ static inline int tg_has_rt_tasks(struct task_group *tg)
>  	struct task_struct *g, *p;
>  
>  	for_each_process_thread(g, p) {
> -		if (rt_task(p) && task_rq(p)->rt.tg == tg)
> +		if (rt_task(p) && task_group(p) == tg)
>  			return 1;
>  	}
>  

[tip:sched/core] sched: Fix the task-group check in tg_has_rt_tasks()

[tip-bot for Oleg Nesterov]

Commit-ID:  8651c65844e93af44554272b7e0d2b142837b244
Gitweb:     http://git.kernel.org/tip/8651c65844e93af44554272b7e0d2b142837b244
Author:     Oleg Nesterov <oleg@redhat.com>
AuthorDate: Sun, 21 Sep 2014 21:33:36 +0200
Committer:  Ingo Molnar <mingo@kernel.org>
CommitDate: Wed, 24 Sep 2014 14:47:00 +0200

sched: Fix the task-group check in tg_has_rt_tasks()

tg_has_rt_tasks() wants to find an RT task in this task_group, but
task_rq(p)->rt.tg wrongly checks the root rt_rq.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Reviewed-by: Kirill Tkhai <ktkhai@parallels.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Mike Galbraith <umgwanakikbuti@gmail.com>
Link: http://lkml.kernel.org/r/20140921193336.GA28618@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 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 09bde2a..0abfb7e 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -7441,7 +7441,7 @@ static inline int tg_has_rt_tasks(struct task_group *tg)
 	struct task_struct *g, *p;
 
 	for_each_process_thread(g, p) {
-		if (rt_task(p) && task_rq(p)->rt.tg == tg)
+		if (rt_task(p) && task_group(p) == tg)
 			return 1;
 	}
 

[tip:sched/core] sched: normalize_rt_tasks(): Don' t use _irqsave for tasklist_lock, use task_rq_lock()

[tip-bot for Oleg Nesterov]

Commit-ID:  3472eaa1f12e217e2b8b0ef658ff861b2308cbbd
Gitweb:     http://git.kernel.org/tip/3472eaa1f12e217e2b8b0ef658ff861b2308cbbd
Author:     Oleg Nesterov <oleg@redhat.com>
AuthorDate: Sun, 21 Sep 2014 21:33:38 +0200
Committer:  Ingo Molnar <mingo@kernel.org>
CommitDate: Wed, 24 Sep 2014 14:47:03 +0200

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>
---
 kernel/sched/core.c | 16 ++++++----------
 1 file changed, 6 insertions(+), 10 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 0abfb7e..d65566d 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 */

[tip:sched/core] sched: print_rq(): Don't use tasklist_lock

[tip-bot for Oleg Nesterov]

Commit-ID:  5bd96ab6fef66ec6b9f54134364e618fd0f8f2f3
Gitweb:     http://git.kernel.org/tip/5bd96ab6fef66ec6b9f54134364e618fd0f8f2f3
Author:     Oleg Nesterov <oleg@redhat.com>
AuthorDate: Sun, 21 Sep 2014 21:33:41 +0200
Committer:  Ingo Molnar <mingo@kernel.org>
CommitDate: Wed, 24 Sep 2014 14:47:04 +0200

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@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/20140921193341.GA28628@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 kernel/sched/debug.c | 7 ++-----
 1 file changed, 2 insertions(+), 5 deletions(-)

diff --git a/kernel/sched/debug.c b/kernel/sched/debug.c
index c7fe1ea0..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");
 }