It's possible that the CPU doing nohz idle balance hasn't had its own
load updated for many seconds. This can lead to huge deltas between
rq->avg_stamp and rq->clock when rebalancing, and has been seen to
cause the following crash:
divide error: 0000 [#1] SMP
Call Trace:
[<ffffffff810bcba8>] update_sd_lb_stats+0xe8/0x560
[<ffffffff810bd04d>] find_busiest_group+0x2d/0x4b0
[<ffffffff810bd640>] load_balance+0x170/0x950
[<ffffffff810be3ff>] rebalance_domains+0x13f/0x290
[<ffffffff810852bc>] __do_softirq+0xec/0x300
[<ffffffff8108578a>] irq_exit+0xfa/0x110
[<ffffffff816167d9>] reschedule_interrupt+0xc9/0xd0
Make sure we update the rq clock and load before balancing.
Cc: Ingo Molnar <mi...@kernel.org>
Cc: Mike Galbraith <umgwanakikb...@gmail.com>
Cc: Peter Zijlstra <pet...@infradead.org>
Signed-off-by: Matt Fleming <m...@codeblueprint.co.uk>
---
kernel/sched/fair.c | 10 ++++++++++
1 file changed, 10 insertions(+)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 2f0a0be4d344..2c81662c858a 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -9597,6 +9597,16 @@ static bool _nohz_idle_balance(struct rq *this_rq,
unsigned int flags,
*/
smp_mb();
+ /*
+ * Ensure this_rq's clock and load are up-to-date before we
+ * rebalance since it's possible that they haven't been
+ * updated for multiple schedule periods, i.e. many seconds.
+ */
+ raw_spin_lock_irq(&this_rq->lock);
+ update_rq_clock(this_rq);
+ cpu_load_update_idle(this_rq);
+ raw_spin_unlock_irq(&this_rq->lock);
+
for_each_cpu(balance_cpu, nohz.idle_cpus_mask) {
if (balance_cpu == this_cpu || !idle_cpu(balance_cpu))
continue;
--
2.13.6
