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From: Paul Turner <pjt@google.com>
To: linux-kernel@vger.kernel.org
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>,
	Ingo Molnar <mingo@elte.hu>, Mike Galbraith <efault@gmx.de>
Subject: [patch 1/5] sched: fix sign under-flows in wake_affine
Date: Fri, 21 Jan 2011 20:44:59 -0800	[thread overview]
Message-ID: <20110122044851.734245014@google.com> (raw)
In-Reply-To: <20110122044458.058531078@google.com>

[-- Attachment #1: sched-signed_wake_affine.patch --]
[-- Type: text/plain, Size: 1246 bytes --]

While care is taken around the zero-point in effective_load to not exceed
the instantaneous rq->weight, it's still possible (e.g. using wake_idx != 0)
for (load + effective_load) to underflow.

In this case the comparing the unsigned values can result in incorrect balanced
decisions.

Signed-off-by: Paul Turner <pjt@google.com>

---
 kernel/sched_fair.c |    6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

Index: tip3/kernel/sched_fair.c
===================================================================
--- tip3.orig/kernel/sched_fair.c
+++ tip3/kernel/sched_fair.c
@@ -1404,7 +1404,7 @@ static inline unsigned long effective_lo
 
 static int wake_affine(struct sched_domain *sd, struct task_struct *p, int sync)
 {
-	unsigned long this_load, load;
+	s64 this_load, load;
 	int idx, this_cpu, prev_cpu;
 	unsigned long tl_per_task;
 	struct task_group *tg;
@@ -1443,8 +1443,8 @@ static int wake_affine(struct sched_doma
 	 * Otherwise check if either cpus are near enough in load to allow this
 	 * task to be woken on this_cpu.
 	 */
-	if (this_load) {
-		unsigned long this_eff_load, prev_eff_load;
+	if (this_load > 0) {
+		s64 this_eff_load, prev_eff_load;
 
 		this_eff_load = 100;
 		this_eff_load *= power_of(prev_cpu);



  reply	other threads:[~2011-01-22  5:04 UTC|newest]

Thread overview: 15+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2011-01-22  4:44 [patch 0/5] scheduler fixlets Paul Turner
2011-01-22  4:44 ` Paul Turner [this message]
2011-01-26 12:09   ` [tip:sched/core] sched: Fix sign under-flows in wake_affine tip-bot for Paul Turner
2011-01-22  4:45 ` [patch 2/5] sched: (cleanup) remove redundant cfs_rq checks Paul Turner
2011-01-26 12:10   ` [tip:sched/core] sched: Fix/remove " tip-bot for Paul Turner
2011-01-22  4:45 ` [patch 3/5] sched: simplify update_cfs_shares parameters Paul Turner
2011-01-26 12:11   ` [tip:sched/core] sched: Simplify " tip-bot for Paul Turner
2011-01-22  4:45 ` [patch 4/5] sched: use rq->clock_task instead of rq->clock for maintaining load averages Paul Turner
2011-01-26 12:10   ` [tip:sched/core] sched: Use rq->clock_task instead of rq->clock for correctly " tip-bot for Paul Turner
2011-01-22  4:45 ` [patch 5/5] sched: avoid expensive initial update_cfs_load() Paul Turner
2011-01-26 12:11   ` [tip:sched/core] sched: Avoid " tip-bot for Paul Turner
2011-01-26 12:36     ` Peter Zijlstra
2011-01-26 12:45   ` [tip:sched/core] sched: Avoid expensive initial update_cfs_load(), on UP too tip-bot for Peter Zijlstra
2011-01-27 11:58   ` tip-bot for Peter Zijlstra
2011-01-24 10:17 ` [patch 0/5] scheduler fixlets Peter Zijlstra

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