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Subject[PATCH] Sched fair: check that ilb cpu is online during nohz_balancer_kick()
Sched fair: check that ilb cpu is online during nohz_balancer_kick()

find_new_ilb() may return offlined cpu if trigger_load_balance() occurs while machine
suspending or resuming, hitting native_smp_send_reschedule() assertion failure:
[ 108.473465] Disabling non-boot CPUs ...
[ 108.477308] CPU 1 is now offline
[ 108.477497] ------------[ cut here ]------------
[ 108.477523] WARNING: at arch/x86/kernel/smp.c:120 native_smp_send_reschedule+0x25/0x56()
[ 108.477724] Call Trace:
[ 108.477736] <IRQ> [<ffffffff81030092>] warn_slowpath_common+0x7e/0x96
[ 108.477772] [<ffffffff810300bf>] warn_slowpath_null+0x15/0x17
[ 108.477795] [<ffffffff81018ff7>] native_smp_send_reschedule+0x25/0x56
[ 108.477823] [<ffffffff81067ffe>] trigger_load_balance+0x6ac/0x72e
[ 108.477847] [<ffffffff81067bfd>] ? trigger_load_balance+0x2ab/0x72e
[ 108.477874] [<ffffffff8105f05c>] scheduler_tick+0xe2/0xeb
[ 108.477899] [<ffffffff8103f6ac>] update_process_times+0x60/0x70
[ 108.477926] [<ffffffff8107c1e1>] tick_sched_timer+0x6d/0x96
[ 108.477951] [<ffffffff81053b3b>] __run_hrtimer+0x1c2/0x3a1
[ 108.477974] [<ffffffff8107c174>] ? tick_nohz_handler+0xdf/0xdf
[ 108.477999] [<ffffffff81054721>] hrtimer_interrupt+0xe6/0x1b0
[ 108.478023] [<ffffffff81019bdd>] smp_apic_timer_interrupt+0x80/0x93
[ 108.478051] [<ffffffff814a2f73>] apic_timer_interrupt+0x73/0x80
[ 108.478072] <EOI> [<ffffffff8148f763>] ? slab_cpuup_callback+0xa8/0xdb
[ 108.478108] [<ffffffff8149f154>] notifier_call_chain+0x86/0xb3
[ 108.478133] [<ffffffff8147f09f>] ? spp_getpage+0x5f/0x5f
[ 108.478157] [<ffffffff810556d9>] __raw_notifier_call_chain+0x9/0xb
[ 108.478182] [<ffffffff81031857>] __cpu_notify+0x1b/0x2d
[ 108.478204] [<ffffffff81031962>] cpu_notify_nofail+0xe/0x16
[ 108.478227] [<ffffffff8147f1fd>] _cpu_down+0x130/0x249
[ 108.478249] [<ffffffff814920ef>] ? printk+0x4c/0x4e
[ 108.478271] [<ffffffff810319f6>] disable_nonboot_cpus+0x5a/0xfc
[ 108.478297] [<ffffffff8106f000>] suspend_devices_and_enter+0x19a/0x407
[ 108.478323] [<ffffffff8106f391>] enter_state+0x124/0x169
[ 108.478346] [<ffffffff8106e01b>] state_store+0xb7/0x101
[ 108.478373] [<ffffffff8126c82f>] kobj_attr_store+0x17/0x19
[ 108.478399] [<ffffffff8117e20c>] sysfs_write_file+0x103/0x13f
[ 108.478425] [<ffffffff8111f018>] vfs_write+0xad/0x13d
[ 108.478447] [<ffffffff8111f293>] sys_write+0x45/0x6c
[ 108.478469] [<ffffffff814a2439>] system_call_fastpath+0x16/0x1b
[ 108.478492] ---[ end trace 991823fa9b0a0b79 ]---

Check that returned by find_new_ilb() cpu is online.

Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>

---

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 84adb2d..070b8e0 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -4826,7 +4826,7 @@ unlock:
rcu_read_unlock();

out_done:
- if (ilb < nr_cpu_ids && idle_cpu(ilb))
+ if (likely(cpu_online(ilb)) && ilb < nr_cpu_ids && idle_cpu(ilb))
return ilb;

return nr_cpu_ids;


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