tick/sched: iowait_sleeptime resides in tick_cpu_sched structure is a negative value

[luanshi <zhangliguang@linux.alibaba.com>]

Hi All,

We encounted a hardlockup problem on ARM server, after some debug found 
that:

PID: 0      TASK: ffff0400064de300  CPU: 126  COMMAND: "swapper/126"
  #0 [ffff8000250f3c90] __crash_kexec at ffff80001013a064
  #1 [ffff8000250f3e30] panic at ffff800010afd028
  #2 [ffff8000250f3f10] nmi_panic at ffff80001004a9e0
  #3 [ffff8000250f3f20] watchdog_hardlockup_check at ffff80001017b7f0
  #4 [ffff8000250f3f40] sdei_watchdog_callback at ffff80001003c9a4
  #5 [ffff8000250f3f50] sdei_event_handler at ffff8000108816b8
  #6 [ffff8000250f3f80] _sdei_handler at ffff800010b1c2e4
  #7 [ffff8000250f3fd0] __sdei_handler at ffff800010b139b0
  #8 [ffff8000250f3ff0] __sdei_asm_handler at ffff800010014c18
--- <IRQ stack> ---
  #9 [ffff800013973f10] __cpu_do_idle at ffff800010b13764
#10 [ffff800013973f20] arch_cpu_idle at ffff800010b137ec
#11 [ffff800013973f30] default_idle_call at ffff800010b1b5cc
#12 [ffff800013973f50] cpuidle_idle_call at ffff80001009648c
#13 [ffff800013973f90] do_idle at ffff8000100965b0
#14 [ffff800013973fc0] cpu_startup_entry at ffff8000100967d4
#15 [ffff800013973fe0] secondary_start_kernel at ffff800010026bb0


per_cpu(tick_cpu_sched, 126) = $1 = {
   sched_timer = {
     node = {
       node = {
         __rb_parent_color = 18446603337117384112,
         rb_right = 0x0,
         rb_left = 0x0
       },
       expires = 6108564000000
     },
     _softexpires = 6108564000000,
     function = 0xffff800010122ec0 <tick_sched_timer>,
     base = 0xffff04473bbcc780,
     state = 1 '\001',
     is_rel = 0 '\000',
     is_soft = 0 '\000',
     is_hard = 1 '\001'
   },
   check_clocks = 0,
   nohz_mode = NOHZ_MODE_INACTIVE,
   inidle = 1,
   tick_stopped = 0,
   idle_active = 1,
   do_timer_last = 0,
   got_idle_tick = 1,
   last_tick = 0,
   next_tick = 0,
   idle_jiffies = 0,
   idle_calls = 0,
   idle_sleeps = 0,
   idle_entrytime = 5012087709249,
   idle_waketime = 0,
   idle_exittime = 0,
   idle_sleeptime = 4936136669951,
   iowait_sleeptime = -1942739704,
   last_jiffies = 0,
   timer_expires = 0,
   timer_expires_base = 0,
   next_timer = 0,
   idle_expires = 0,
   tick_dep_mask = {
     counter = 0
   }
}

iowait_sleeptime = -1942739704,
----------
iowait_sleeptime is monotonically increasing, under what circumstances 
iowait_sleeptime
can be a negative value?

For detailed information:
https://bugzilla.kernel.org/show_bug.cgi?id=215458


Can you give me some suggestions for debugging.



Thanks,
Liguang