diff options
| author | Xie XiuQi <xiexiuqi@huawei.com> | 2019-04-20 16:34:16 +0800 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2019-05-02 09:40:29 +0200 |
| commit | e4713de969c4b20a71fd3905af19e8b3904e7425 (patch) | |
| tree | 334d540150b09c21540017a593dc1a88de528d57 /kernel | |
| parent | daff434656562c3c8c9328945156ff241448d521 (diff) | |
sched/numa: Fix a possible divide-by-zero
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>
Diffstat (limited to 'kernel')
| -rw-r--r-- | kernel/sched/fair.c | 4 |
1 files changed, 4 insertions, 0 deletions
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index a5d163903835..af7de1f9906c 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -2026,6 +2026,10 @@ 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 / p->se.load.weight; *period = LOAD_AVG_MAX; |