Messages in this thread Patch in this message | | | Date | Thu, 25 Apr 2019 11:04:05 -0700 | From | tip-bot for Xie XiuQi <> | Subject | [tip:sched/urgent] sched/numa: Fix a possible divide-by-zero |
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Commit-ID: a860fa7b96e1a1c974556327aa1aee852d434c21 Gitweb: https://git.kernel.org/tip/a860fa7b96e1a1c974556327aa1aee852d434c21 Author: Xie XiuQi <xiexiuqi@huawei.com> AuthorDate: Sat, 20 Apr 2019 16:34:16 +0800 Committer: Ingo Molnar <mingo@kernel.org> CommitDate: Thu, 25 Apr 2019 19:58:54 +0200
sched/numa: Fix a possible divide-by-zero
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> --- kernel/sched/fair.c | 4 ++++ 1 file changed, 4 insertions(+)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index a4d9e14bf138..35f3ea375084 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -2007,6 +2007,10 @@ static u64 numa_get_avg_runtime(struct task_struct *p, u64 *period) 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;
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