| From | Ben Hutchings <> | Date | Sat, 10 Aug 2019 21:40:07 +0100 | Subject | [PATCH 3.16 110/157] sched/numa: Fix a possible divide-by-zero |
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3.16.72-rc1 review patch. If anyone has any objections, please let me know.
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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 Link: http://lkml.kernel.org/r/20190425080016.GX11158@hirez.programming.kicks-ass.net Signed-off-by: Ingo Molnar <mingo@kernel.org> Signed-off-by: Ben Hutchings <ben@decadent.org.uk> --- kernel/sched/fair.c | 4 ++++ 1 file changed, 4 insertions(+)
--- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -1503,6 +1503,10 @@ 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.runnable_avg_sum; *period = p->se.avg.runnable_avg_period;
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