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authorSteven Rostedt <rostedt@goodmis.org>2008-11-26 21:04:24 -0500
committerIngo Molnar <mingo@elte.hu>2008-11-27 10:29:52 +0100
commit4cd4262034849da01eb88659af677b69f8169f06 (patch)
treeeaab94e7fd4a436bcead7efd6684405252f336c4 /kernel
parentee2f6cc7f9ea2542ad46070ed62ba7aa04d08871 (diff)
sched: prevent divide by zero error in cpu_avg_load_per_task
Impact: fix divide by zero crash in scheduler rebalance irq While testing the branch profiler, I hit this crash: divide error: 0000 [#1] PREEMPT SMP [...] RIP: 0010:[<ffffffff8024a008>] [<ffffffff8024a008>] cpu_avg_load_per_task+0x50/0x7f [...] Call Trace: <IRQ> <0> [<ffffffff8024fd43>] find_busiest_group+0x3e5/0xcaa [<ffffffff8025da75>] rebalance_domains+0x2da/0xa21 [<ffffffff80478769>] ? find_next_bit+0x1b2/0x1e6 [<ffffffff8025e2ce>] run_rebalance_domains+0x112/0x19f [<ffffffff8026d7c2>] __do_softirq+0xa8/0x232 [<ffffffff8020ea7c>] call_softirq+0x1c/0x3e [<ffffffff8021047a>] do_softirq+0x94/0x1cd [<ffffffff8026d5eb>] irq_exit+0x6b/0x10e [<ffffffff8022e6ec>] smp_apic_timer_interrupt+0xd3/0xff [<ffffffff8020e4b3>] apic_timer_interrupt+0x13/0x20 The code for cpu_avg_load_per_task has: if (rq->nr_running) rq->avg_load_per_task = rq->load.weight / rq->nr_running; The runqueue lock is not held here, and there is nothing that prevents the rq->nr_running from going to zero after it passes the if condition. The branch profiler simply made the race window bigger. This patch saves off the rq->nr_running to a local variable and uses that for both the condition and the division. Signed-off-by: Steven Rostedt <srostedt@redhat.com> Peter Zijlstra <peterz@infradead.org> Signed-off-by: Ingo Molnar <mingo@elte.hu>
Diffstat (limited to 'kernel')
-rw-r--r--kernel/sched.c5
1 files changed, 3 insertions, 2 deletions
diff --git a/kernel/sched.c b/kernel/sched.c
index 9b1e79371c20..700aa9a1413f 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -1453,9 +1453,10 @@ static int task_hot(struct task_struct *p, u64 now, struct sched_domain *sd);
static unsigned long cpu_avg_load_per_task(int cpu)
{
struct rq *rq = cpu_rq(cpu);
+ unsigned long nr_running = rq->nr_running;
- if (rq->nr_running)
- rq->avg_load_per_task = rq->load.weight / rq->nr_running;
+ if (nr_running)
+ rq->avg_load_per_task = rq->load.weight / nr_running;
else
rq->avg_load_per_task = 0;