| From a860fa7b96e1a1c974556327aa1aee852d434c21 Mon Sep 17 00:00:00 2001 |
| From: Xie XiuQi <xiexiuqi@huawei.com> |
| Date: Sat, 20 Apr 2019 16:34:16 +0800 |
| Subject: sched/numa: Fix a possible divide-by-zero |
| |
| From: Xie XiuQi <xiexiuqi@huawei.com> |
| |
| commit a860fa7b96e1a1c974556327aa1aee852d434c21 upstream. |
| |
| sched_clock_cpu() may not be consistent between CPUs. If a task |
| migrates to another CPU, then se.exec_start is set to that CPU's |
| rq_clock_task() by update_stats_curr_start(). Specifically, the new |
| value might be before the old value due to clock skew. |
| |
| So then if in numa_get_avg_runtime() the expression: |
| |
| 'now - p->last_task_numa_placement' |
| |
| ends up as -1, then the divider '*period + 1' in task_numa_placement() |
| is 0 and things go bang. Similar to update_curr(), check if time goes |
| backwards to avoid this. |
| |
| [ peterz: Wrote new changelog. ] |
| [ mingo: Tweaked the code comment. ] |
| |
| Signed-off-by: Xie XiuQi <xiexiuqi@huawei.com> |
| Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> |
| Cc: Linus Torvalds <torvalds@linux-foundation.org> |
| Cc: Peter Zijlstra <peterz@infradead.org> |
| Cc: Thomas Gleixner <tglx@linutronix.de> |
| Cc: cj.chengjian@huawei.com |
| Cc: <stable@vger.kernel.org> |
| Link: http://lkml.kernel.org/r/20190425080016.GX11158@hirez.programming.kicks-ass.net |
| Signed-off-by: Ingo Molnar <mingo@kernel.org> |
| Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> |
| |
| --- |
| kernel/sched/fair.c | 4 ++++ |
| 1 file changed, 4 insertions(+) |
| |
| --- a/kernel/sched/fair.c |
| +++ b/kernel/sched/fair.c |
| @@ -1994,6 +1994,10 @@ static u64 numa_get_avg_runtime(struct t |
| if (p->last_task_numa_placement) { |
| delta = runtime - p->last_sum_exec_runtime; |
| *period = now - p->last_task_numa_placement; |
| + |
| + /* Avoid time going backwards, prevent potential divide error: */ |
| + if (unlikely((s64)*period < 0)) |
| + *period = 0; |
| } else { |
| delta = p->se.avg.load_sum; |
| *period = LOAD_AVG_MAX; |