linux-kernel - Re: 2.6.23-rc7-mm1: panic in scheduler

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Message-ID: <20070924222409.GA28997@elte.hu>
Date:	Tue, 25 Sep 2007 00:24:09 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Lee Schermerhorn <Lee.Schermerhorn@...com>
Cc:	linux-kernel <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Dmitry Adamushko <dmitry.adamushko@...il.com>
Subject: Re: 2.6.23-rc7-mm1:  panic in scheduler


* Lee Schermerhorn <Lee.Schermerhorn@...com> wrote:

> Taking a quick look at [__]{en|de|queue_entity() and the functions 
> they call, I see something suspicious in set_leftmost() in 
> sched_fair.c:
> 
> static inline void
> set_leftmost(struct cfs_rq *cfs_rq, struct rb_node *leftmost)
> {
>         struct sched_entity *se;
> 
>         cfs_rq->rb_leftmost = leftmost;
>         if (leftmost)
>                 se = rb_entry(leftmost, struct sched_entity, run_node);
> }
> 
> Missing code?  corrupt patch?

could you pull this git tree ontop of a -rc7 (or later) upstream tree:

  git-pull git://git.kernel.org/pub/scm/linux/kernel/git/mingo/linux-2.6-sched-devel.git

does the solve the crash?

the above set_leftmost() code used to be larger and now indeed those 
bits are mostly dead code. I've queued up a clean-up patch for that - 
see the patch below. It should not impact correctness though, so if you 
can still trigger the crash with the latest sched-devel.git tree we'd 
like to know about it.

	Ingo

------------------->
Subject: sched: remove set_leftmost()
From: Ingo Molnar <mingo@...e.hu>

Lee Schermerhorn noticed that set_leftmost() contains dead code,
remove this.

Reported-by: Lee Schermerhorn <Lee.Schermerhorn@...com>
Signed-off-by: Ingo Molnar <mingo@...e.hu>
---
 kernel/sched_fair.c |   14 ++------------
 1 file changed, 2 insertions(+), 12 deletions(-)

Index: linux/kernel/sched_fair.c
===================================================================
--- linux.orig/kernel/sched_fair.c
+++ linux/kernel/sched_fair.c
@@ -124,16 +124,6 @@ max_vruntime(u64 min_vruntime, u64 vrunt
 	return min_vruntime;
 }
 
-static inline void
-set_leftmost(struct cfs_rq *cfs_rq, struct rb_node *leftmost)
-{
-	struct sched_entity *se;
-
-	cfs_rq->rb_leftmost = leftmost;
-	if (leftmost)
-		se = rb_entry(leftmost, struct sched_entity, run_node);
-}
-
 static inline s64
 entity_key(struct cfs_rq *cfs_rq, struct sched_entity *se)
 {
@@ -175,7 +165,7 @@ __enqueue_entity(struct cfs_rq *cfs_rq, 
 	 * used):
 	 */
 	if (leftmost)
-		set_leftmost(cfs_rq, &se->run_node);
+		cfs_rq->rb_leftmost = &se->run_node;
 
 	rb_link_node(&se->run_node, parent, link);
 	rb_insert_color(&se->run_node, &cfs_rq->tasks_timeline);
@@ -185,7 +175,7 @@ static void
 __dequeue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se)
 {
 	if (cfs_rq->rb_leftmost == &se->run_node)
-		set_leftmost(cfs_rq, rb_next(&se->run_node));
+		cfs_rq->rb_leftmost = rb_next(&se->run_node);
 
 	rb_erase(&se->run_node, &cfs_rq->tasks_timeline);
 }
-
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