[PATCH] sched: fix rt_nr_migratory corruption raised in push_rt_task()

[PATCH] sched: fix rt_nr_migratory corruption raised in push_rt_task()

[Hillf Danton]

When pushing, if a pushable task could not be pushed, it is dequeued with no
updating the rt_nr_migratory element of RT run-queue, then rt_nr_migratory is
corrupted, which is fixed by removing the dequeue operation.

Signed-off-by: Hillf Danton <dhillf@gmail.com>
---
 kernel/sched_rt.c |    5 +++--
 1 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/kernel/sched_rt.c b/kernel/sched_rt.c
index 88725c9..496e06a 100644
--- a/kernel/sched_rt.c
+++ b/kernel/sched_rt.c
@@ -1378,6 +1378,7 @@ static int push_rt_task(struct rq *rq)
 {
 	struct task_struct *next_task;
 	struct rq *lowest_rq;
+	int ret = 1;

 	if (!rq->rt.overloaded)
 		return 0;
@@ -1425,7 +1426,7 @@ retry:
 			 * since the other cpus will pull from us when they
 			 * are ready.
 			 */
-			dequeue_pushable_task(rq, next_task);
+			ret = 0;
 			goto out;
 		}

@@ -1452,7 +1453,7 @@ retry:
 out:
 	put_task_struct(next_task);

-	return 1;
+	return ret;
 }

 static void push_rt_tasks(struct rq *rq)

Re: [PATCH] sched: fix rt_nr_migratory corruption raised in push_rt_task()

[Mike Galbraith]

On Mon, 2011-05-30 at 21:39 +0800, Hillf Danton wrote:
> When pushing, if a pushable task could not be pushed, it is dequeued with no
> updating the rt_nr_migratory element of RT run-queue, then rt_nr_migratory is
> corrupted, which is fixed by removing the dequeue operation.

Hm.  I think you're right that this dequeue_pushable_task() call can be
removed, at least I didn't see it's reason for existing.  I'd word it a
bit differently though, and not return 1 unless we really did push.

From: Hillf Danton <dhillf@gmail.com>

sched, rt: fix rq->rt.pushable_tasks bug in push_rt_task()

Do not call dequeue_pushable_task() when failing to push an eligible
task, as it remains pushable, merely not at this particular moment.

Signed-off-by: Hillf Danton <dhillf@gmail.com>
---
 kernel/sched_rt.c |   15 ++++++++-------
 1 file changed, 8 insertions(+), 7 deletions(-)

Index: linux-2.6.40.git/kernel/sched_rt.c
===================================================================
--- linux-2.6.40.git.orig/kernel/sched_rt.c
+++ linux-2.6.40.git/kernel/sched_rt.c
@@ -1378,6 +1378,7 @@ static int push_rt_task(struct rq *rq)
 {
 	struct task_struct *next_task;
 	struct rq *lowest_rq;
+	int ret = 0;
 
 	if (!rq->rt.overloaded)
 		return 0;
@@ -1410,7 +1411,7 @@ retry:
 	if (!lowest_rq) {
 		struct task_struct *task;
 		/*
-		 * find lock_lowest_rq releases rq->lock
+		 * find_lock_lowest_rq releases rq->lock
 		 * so it is possible that next_task has migrated.
 		 *
 		 * We need to make sure that the task is still on the same
@@ -1420,12 +1421,11 @@ retry:
 		task = pick_next_pushable_task(rq);
 		if (task_cpu(next_task) == rq->cpu && task == next_task) {
 			/*
-			 * If we get here, the task hasn't moved at all, but
-			 * it has failed to push.  We will not try again,
-			 * since the other cpus will pull from us when they
-			 * are ready.
+			 * The task hasn't migrated, and is still the next
+			 * eligible task, but we failed to find a run-queue
+			 * to push it to.  Do not retry in this case, since
+			 * other cpus will pull from us when ready.
 			 */
-			dequeue_pushable_task(rq, next_task);
 			goto out;
 		}
 
@@ -1444,6 +1444,7 @@ retry:
 	deactivate_task(rq, next_task, 0);
 	set_task_cpu(next_task, lowest_rq->cpu);
 	activate_task(lowest_rq, next_task, 0);
+	ret = 1;
 
 	resched_task(lowest_rq->curr);
 
@@ -1452,7 +1453,7 @@ retry:
 out:
 	put_task_struct(next_task);
 
-	return 1;
+	return ret;
 }
 
 static void push_rt_tasks(struct rq *rq)

Re: [PATCH] sched: fix rt_nr_migratory corruption raised in push_rt_task()

[Hillf Danton]

On Tue, May 31, 2011 at 3:36 PM, Mike Galbraith <efault@gmx.de> wrote:
> On Mon, 2011-05-30 at 21:39 +0800, Hillf Danton wrote:
>> When pushing, if a pushable task could not be pushed, it is dequeued with no
>> updating the rt_nr_migratory element of RT run-queue, then rt_nr_migratory is
>> corrupted, which is fixed by removing the dequeue operation.
>
> Hm.  I think you're right that this dequeue_pushable_task() call can be
> removed, at least I didn't see it's reason for existing.  I'd word it a
> bit differently though, and not return 1 unless we really did push.
>

Hi Mike

Your message shows what is called professional work, but something lost,

> From: Hillf Danton <dhillf@gmail.com>
>
> sched, rt: fix rq->rt.pushable_tasks bug in push_rt_task()
>
> Do not call dequeue_pushable_task() when failing to push an eligible
> task, as it remains pushable, merely not at this particular moment.
>
> Signed-off-by: Hillf Danton <dhillf@gmail.com>

Signed-off-by: Mike Galbraith <efault@gmx.de>

right?

> ---
>  kernel/sched_rt.c |   15 ++++++++-------
>  1 file changed, 8 insertions(+), 7 deletions(-)
>
> Index: linux-2.6.40.git/kernel/sched_rt.c
> ===================================================================

And how to drive git to print the above two lines?

thanks
            Hillf

Re: [PATCH] sched: fix rt_nr_migratory corruption raised in push_rt_task()

[Steven Rostedt]

On Tue, 2011-05-31 at 21:56 +0800, Hillf Danton wrote:
> On Tue, May 31, 2011 at 3:36 PM, Mike Galbraith <efault@gmx.de> wrote:
> > On Mon, 2011-05-30 at 21:39 +0800, Hillf Danton wrote:
> >> When pushing, if a pushable task could not be pushed, it is dequeued with no
> >> updating the rt_nr_migratory element of RT run-queue, then rt_nr_migratory is
> >> corrupted, which is fixed by removing the dequeue operation.
> >
> > Hm.  I think you're right that this dequeue_pushable_task() call can be
> > removed, at least I didn't see it's reason for existing.  I'd word it a
> > bit differently though, and not return 1 unless we really did push.
> >
> 
> Hi Mike
> 
> Your message shows what is called professional work, but something lost,
> 
> > From: Hillf Danton <dhillf@gmail.com>
> >
> > sched, rt: fix rq->rt.pushable_tasks bug in push_rt_task()
> >
> > Do not call dequeue_pushable_task() when failing to push an eligible
> > task, as it remains pushable, merely not at this particular moment.
> >
> > Signed-off-by: Hillf Danton <dhillf@gmail.com>
> 
> Signed-off-by: Mike Galbraith <efault@gmx.de>
> 

Yeah, Mike, can you remail this adding your SOB too. You can keep
Hillf's SOB as well, since both of you made changes.

Thanks!

-- Steve

[PATCH] sched, rt: fix rq->rt.pushable_tasks bug in push_rt_task()

[Mike Galbraith]

On Tue, 2011-05-31 at 11:08 -0400, Steven Rostedt wrote:
> On Tue, 2011-05-31 at 21:56 +0800, Hillf Danton wrote:
> > On Tue, May 31, 2011 at 3:36 PM, Mike Galbraith <efault@gmx.de> wrote:
> > > On Mon, 2011-05-30 at 21:39 +0800, Hillf Danton wrote:
> > >> When pushing, if a pushable task could not be pushed, it is dequeued with no
> > >> updating the rt_nr_migratory element of RT run-queue, then rt_nr_migratory is
> > >> corrupted, which is fixed by removing the dequeue operation.
> > >
> > > Hm.  I think you're right that this dequeue_pushable_task() call can be
> > > removed, at least I didn't see it's reason for existing.  I'd word it a
> > > bit differently though, and not return 1 unless we really did push.
> > >
> > 
> > Hi Mike
> > 
> > Your message shows what is called professional work, but something lost,
> > 
> > > From: Hillf Danton <dhillf@gmail.com>
> > >
> > > sched, rt: fix rq->rt.pushable_tasks bug in push_rt_task()
> > >
> > > Do not call dequeue_pushable_task() when failing to push an eligible
> > > task, as it remains pushable, merely not at this particular moment.
> > >
> > > Signed-off-by: Hillf Danton <dhillf@gmail.com>
> > 
> > Signed-off-by: Mike Galbraith <efault@gmx.de>
> > 
> 
> Yeah, Mike, can you remail this adding your SOB too. You can keep
> Hillf's SOB as well, since both of you made changes.

From: Hillf Danton <dhillf@gmail.com>
AuthorDate: Mon, 30 May 2011 21:39:50 +0800

sched, rt: fix rq->rt.pushable_tasks bug in push_rt_task()

Do not call dequeue_pushable_task() when failing to push an eligible
task, as it remains pushable until either it's cpumask says otherwise,
or is selected.  It is merely not pushable at this particular moment.

Signed-off-by: Hillf Danton <dhillf@gmail.com>
Signed-off-by: Mike Galbraith <efault@gmx.de>
---
 kernel/sched_rt.c |   15 ++++++++-------
 1 file changed, 8 insertions(+), 7 deletions(-)

Index: linux-2.6.40.git/kernel/sched_rt.c
===================================================================
--- linux-2.6.40.git.orig/kernel/sched_rt.c
+++ linux-2.6.40.git/kernel/sched_rt.c
@@ -1378,6 +1378,7 @@ static int push_rt_task(struct rq *rq)
 {
 	struct task_struct *next_task;
 	struct rq *lowest_rq;
+	int ret = 0;
 
 	if (!rq->rt.overloaded)
 		return 0;
@@ -1410,7 +1411,7 @@ retry:
 	if (!lowest_rq) {
 		struct task_struct *task;
 		/*
-		 * find lock_lowest_rq releases rq->lock
+		 * find_lock_lowest_rq releases rq->lock
 		 * so it is possible that next_task has migrated.
 		 *
 		 * We need to make sure that the task is still on the same
@@ -1420,12 +1421,11 @@ retry:
 		task = pick_next_pushable_task(rq);
 		if (task_cpu(next_task) == rq->cpu && task == next_task) {
 			/*
-			 * If we get here, the task hasn't moved at all, but
-			 * it has failed to push.  We will not try again,
-			 * since the other cpus will pull from us when they
-			 * are ready.
+			 * The task hasn't migrated, and is still the next
+			 * eligible task, but we failed to find a run-queue
+			 * to push it to.  Do not retry in this case, since
+			 * other cpus will pull from us when ready.
 			 */
-			dequeue_pushable_task(rq, next_task);
 			goto out;
 		}
 
@@ -1444,6 +1444,7 @@ retry:
 	deactivate_task(rq, next_task, 0);
 	set_task_cpu(next_task, lowest_rq->cpu);
 	activate_task(lowest_rq, next_task, 0);
+	ret = 1;
 
 	resched_task(lowest_rq->curr);
 
@@ -1452,7 +1453,7 @@ retry:
 out:
 	put_task_struct(next_task);
 
-	return 1;
+	return ret;
 }
 
 static void push_rt_tasks(struct rq *rq)

Re: [PATCH] sched, rt: fix rq->rt.pushable_tasks bug in push_rt_task()

[Mike Galbraith]

Stupid mouse (driver) grabbed wrong text blob.

From: Hillf Danton <dhillf@gmail.com>

sched, rt: fix rq->rt.pushable_tasks bug in push_rt_task()

Do not call dequeue_pushable_task() when failing to push an eligible
task, as it remains pushable, merely not at this particular moment.

Signed-off-by: Hillf Danton <dhillf@gmail.com>
Signed-off-by: Mike Galbraith <mgalbraith@gmx.de>
---
 kernel/sched_rt.c |   15 ++++++++-------
 1 file changed, 8 insertions(+), 7 deletions(-)

Index: linux-2.6.40.git/kernel/sched_rt.c
===================================================================
--- linux-2.6.40.git.orig/kernel/sched_rt.c
+++ linux-2.6.40.git/kernel/sched_rt.c
@@ -1378,6 +1378,7 @@ static int push_rt_task(struct rq *rq)
 {
 	struct task_struct *next_task;
 	struct rq *lowest_rq;
+	int ret = 0;
 
 	if (!rq->rt.overloaded)
 		return 0;
@@ -1410,7 +1411,7 @@ retry:
 	if (!lowest_rq) {
 		struct task_struct *task;
 		/*
-		 * find lock_lowest_rq releases rq->lock
+		 * find_lock_lowest_rq releases rq->lock
 		 * so it is possible that next_task has migrated.
 		 *
 		 * We need to make sure that the task is still on the same
@@ -1420,12 +1421,11 @@ retry:
 		task = pick_next_pushable_task(rq);
 		if (task_cpu(next_task) == rq->cpu && task == next_task) {
 			/*
-			 * If we get here, the task hasn't moved at all, but
-			 * it has failed to push.  We will not try again,
-			 * since the other cpus will pull from us when they
-			 * are ready.
+			 * The task hasn't migrated, and is still the next
+			 * eligible task, but we failed to find a run-queue
+			 * to push it to.  Do not retry in this case, since
+			 * other cpus will pull from us when ready.
 			 */
-			dequeue_pushable_task(rq, next_task);
 			goto out;
 		}
 
@@ -1444,6 +1444,7 @@ retry:
 	deactivate_task(rq, next_task, 0);
 	set_task_cpu(next_task, lowest_rq->cpu);
 	activate_task(lowest_rq, next_task, 0);
+	ret = 1;
 
 	resched_task(lowest_rq->curr);
 
@@ -1452,7 +1453,7 @@ retry:
 out:
 	put_task_struct(next_task);
 
-	return 1;
+	return ret;
 }
 
 static void push_rt_tasks(struct rq *rq)

[tip:sched/core] sched, rt: Fix rq->rt.pushable_tasks bug in push_rt_task()

[tip-bot for Hillf Danton]

Commit-ID:  311e800e16f63d909136a64ed17ca353a160be59
Gitweb:     http://git.kernel.org/tip/311e800e16f63d909136a64ed17ca353a160be59
Author:     Hillf Danton <dhillf@gmail.com>
AuthorDate: Thu, 16 Jun 2011 21:55:20 -0400
Committer:  Ingo Molnar <mingo@elte.hu>
CommitDate: Sun, 14 Aug 2011 12:00:48 +0200

sched, rt: Fix rq->rt.pushable_tasks bug in push_rt_task()

Do not call dequeue_pushable_task() when failing to push an eligible
task, as it remains pushable, merely not at this particular moment.

Signed-off-by: Hillf Danton <dhillf@gmail.com>
Signed-off-by: Mike Galbraith <mgalbraith@gmx.de>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Yong Zhang <yong.zhang0@gmail.com>
Link: http://lkml.kernel.org/r/1306895385.4791.26.camel@marge.simson.net
Signed-off-by: Ingo Molnar <mingo@elte.hu>
---
 kernel/sched_rt.c |   15 ++++++++-------
 1 files changed, 8 insertions(+), 7 deletions(-)

diff --git a/kernel/sched_rt.c b/kernel/sched_rt.c
index e2698c0..8e18945 100644
--- a/kernel/sched_rt.c
+++ b/kernel/sched_rt.c
@@ -1394,6 +1394,7 @@ static int push_rt_task(struct rq *rq)
 {
 	struct task_struct *next_task;
 	struct rq *lowest_rq;
+	int ret = 0;
 
 	if (!rq->rt.overloaded)
 		return 0;
@@ -1426,7 +1427,7 @@ retry:
 	if (!lowest_rq) {
 		struct task_struct *task;
 		/*
-		 * find lock_lowest_rq releases rq->lock
+		 * find_lock_lowest_rq releases rq->lock
 		 * so it is possible that next_task has migrated.
 		 *
 		 * We need to make sure that the task is still on the same
@@ -1436,12 +1437,11 @@ retry:
 		task = pick_next_pushable_task(rq);
 		if (task_cpu(next_task) == rq->cpu && task == next_task) {
 			/*
-			 * If we get here, the task hasn't moved at all, but
-			 * it has failed to push.  We will not try again,
-			 * since the other cpus will pull from us when they
-			 * are ready.
+			 * The task hasn't migrated, and is still the next
+			 * eligible task, but we failed to find a run-queue
+			 * to push it to.  Do not retry in this case, since
+			 * other cpus will pull from us when ready.
 			 */
-			dequeue_pushable_task(rq, next_task);
 			goto out;
 		}
 
@@ -1460,6 +1460,7 @@ retry:
 	deactivate_task(rq, next_task, 0);
 	set_task_cpu(next_task, lowest_rq->cpu);
 	activate_task(lowest_rq, next_task, 0);
+	ret = 1;
 
 	resched_task(lowest_rq->curr);
 
@@ -1468,7 +1469,7 @@ retry:
 out:
 	put_task_struct(next_task);
 
-	return 1;
+	return ret;
 }
 
 static void push_rt_tasks(struct rq *rq)

Re: [PATCH] sched: fix rt_nr_migratory corruption raised in push_rt_task()

[Mike Galbraith]

On Tue, 2011-05-31 at 21:56 +0800, Hillf Danton wrote:
> On Tue, May 31, 2011 at 3:36 PM, Mike Galbraith <efault@gmx.de> wrote:
> > On Mon, 2011-05-30 at 21:39 +0800, Hillf Danton wrote:
> >> When pushing, if a pushable task could not be pushed, it is dequeued with no
> >> updating the rt_nr_migratory element of RT run-queue, then rt_nr_migratory is
> >> corrupted, which is fixed by removing the dequeue operation.
> >
> > Hm.  I think you're right that this dequeue_pushable_task() call can be
> > removed, at least I didn't see it's reason for existing.  I'd word it a
> > bit differently though, and not return 1 unless we really did push.
> >
> 
> Hi Mike
> 
> Your message shows what is called professional work, but something lost,
> 
> > From: Hillf Danton <dhillf@gmail.com>
> >
> > sched, rt: fix rq->rt.pushable_tasks bug in push_rt_task()
> >
> > Do not call dequeue_pushable_task() when failing to push an eligible
> > task, as it remains pushable, merely not at this particular moment.
> >
> > Signed-off-by: Hillf Danton <dhillf@gmail.com>
> 
> Signed-off-by: Mike Galbraith <efault@gmx.de>
> 
> right?

Well, you did the legwork, but I resent it as requested.

> > ---
> >  kernel/sched_rt.c |   15 ++++++++-------
> >  1 file changed, 8 insertions(+), 7 deletions(-)
> >
> > Index: linux-2.6.40.git/kernel/sched_rt.c
> > ===================================================================
> 
> And how to drive git to print the above two lines?

That's easy, I used quilt :)  I'm no master of git-fu (wimpy whitebelt),
use git for hunting, but quilt for twiddling.

	-Mike