[-mm patch] Avoid divide by zero errors in sched.c

[-mm patch] Avoid divide by zero errors in sched.c

[Dave Kleikamp]

This patch fixes a divide-by-zero error that I hit on a two-way i386
machine.  rq->nr_running is tested to be non-zero, but may change by the
time it is used in the division.  Saving the value to a local variable
ensures that the same value that is checked is used in the division.

Signed-off-by: Dave Kleikamp <shaggy@austin.ibm.com>
Cc: Con Kolivas <kernel@kolivas.org>

diff -urp linux-2.6.13-rc5-mm1/kernel/sched.c linux/kernel/sched.c
--- linux-2.6.13-rc5-mm1/kernel/sched.c	2005-08-11 09:41:30.000000000 -0500
+++ linux/kernel/sched.c	2005-08-11 09:47:27.000000000 -0500
@@ -989,15 +989,16 @@ void kick_process(task_t *p)
 static inline unsigned long __source_load(int cpu, int type, enum idle_type idle)
 {
 	runqueue_t *rq = cpu_rq(cpu);
+	unsigned long running = rq->nr_running;
 	unsigned long source_load, cpu_load = rq->cpu_load[type-1],
-		load_now = rq->nr_running * SCHED_LOAD_SCALE;
+		load_now = running * SCHED_LOAD_SCALE;
 
 	if (type == 0)
 		source_load = load_now;
 	else
 		source_load = min(cpu_load, load_now);
 
-	if (rq->nr_running > 1 || (idle == NOT_IDLE && rq->nr_running))
+	if (running > 1 || (idle == NOT_IDLE && running))
 		/*
 		 * If we are busy rebalancing the load is biased by
 		 * priority to create 'nice' support across cpus. When
@@ -1006,7 +1007,7 @@ static inline unsigned long __source_loa
 		 * prevent idle rebalance from trying to pull tasks from a
 		 * queue with only one running task.
 		 */
-		source_load = source_load * rq->prio_bias / rq->nr_running;
+		source_load = source_load * rq->prio_bias / running;
 
 	return source_load;
 }
@@ -1022,16 +1023,17 @@ static inline unsigned long source_load(
 static inline unsigned long __target_load(int cpu, int type, enum idle_type idle)
 {
 	runqueue_t *rq = cpu_rq(cpu);
+	unsigned long running = rq->nr_running;
 	unsigned long target_load, cpu_load = rq->cpu_load[type-1],
-		load_now = rq->nr_running * SCHED_LOAD_SCALE;
+		load_now = running * SCHED_LOAD_SCALE;
 
 	if (type == 0)
 		target_load = load_now;
 	else
 		target_load = max(cpu_load, load_now);
 
-	if (rq->nr_running > 1 || (idle == NOT_IDLE && rq->nr_running))
-		target_load = target_load * rq->prio_bias / rq->nr_running;
+	if (running > 1 || (idle == NOT_IDLE && running))
+		target_load = target_load * rq->prio_bias / running;
 
 	return target_load;
 }

-- 
David Kleikamp
IBM Linux Technology Center

Re: [-mm patch] Avoid divide by zero errors in sched.c

[Con Kolivas]

On Fri, 12 Aug 2005 23:10, Dave Kleikamp wrote:
> This patch fixes a divide-by-zero error that I hit on a two-way i386
> machine.  rq->nr_running is tested to be non-zero, but may change by the
> time it is used in the division.  Saving the value to a local variable
> ensures that the same value that is checked is used in the division.
>
> Signed-off-by: Dave Kleikamp <shaggy@austin.ibm.com>

Acked-by: Con Kolivas <kernel@kolivas.org>