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 09:58:54 +0200 |
| commit | 9b8c07129ddfeec6394b44b42d4e54639ac498c0 (patch) | |
| tree | 973c32045781ae4aadb6488ac088d37bb0040146 /kernel/sched/fair.c | |
| parent | 1af34bf97eca3624b5f2ec786527c8609e1a68b8 (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/sched/fair.c')
| -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 4aa8e7d90c25..d31916366d39 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -2016,6 +2016,10 @@ 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; |