From: Xie XiuQi <xiexi...@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 <xiexi...@huawei.com> Signed-off-by: Peter Zijlstra (Intel) <pet...@infradead.org> Cc: Linus Torvalds <torva...@linux-foundation.org> Cc: Peter Zijlstra <pet...@infradead.org> Cc: Thomas Gleixner <t...@linutronix.de> Cc: cj.chengj...@huawei.com Cc: <sta...@vger.kernel.org> Link: http://lkml.kernel.org/r/20190425080016.gx11...@hirez.programming.kicks-ass.net Signed-off-by: Ingo Molnar <mi...@kernel.org> Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org> --- kernel/sched/fair.c | 4 ++++ 1 file changed, 4 insertions(+) --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -1722,6 +1722,10 @@ 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 / p->se.load.weight; *period = LOAD_AVG_MAX;
