linux-kernel - Re: hung task in 4.14 (syzbot bug from 2018 April 17)

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Date:   Fri, 5 Oct 2018 15:56:02 -0600
From:   Sebastian Kuzminsky <seb.kuzminsky@...il.com>
To:     linux-kernel@...r.kernel.org
Subject: Re: hung task in 4.14 (syzbot bug from 2018 April 17)

Another instance of the same problem (also on 4.14.67), this time with
the hung task timeout restored to its 120 second default:

[  980.954129] INFO: task systemd:1 blocked for more than 120 seconds.
[  980.954132]       Tainted: G           OE   4.14.67-solidfire1 #1
[  980.954133] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs"
disables this message.
[  980.954135] systemd         D    0     1      0 0x00000000
[  980.954137] Call Trace:
[  980.954150]  ? __schedule+0x27f/0x870
[  980.954154]  ? check_preempt_wakeup+0x102/0x230
[  980.954156]  schedule+0x28/0x80
[  980.954159]  schedule_timeout+0x1e7/0x340
[  980.954163]  ? radix_tree_node_ctor+0x20/0x20
[  980.954165]  ? delete_node+0x1b8/0x1f0
[  980.954167]  ? wait_for_completion+0xb0/0x120
[  980.954169]  wait_for_completion+0xb0/0x120
[  980.954172]  ? wake_up_q+0x70/0x70
[  980.954176]  flush_work+0x10d/0x1c0
[  980.954179]  ? worker_detach_from_pool+0xa0/0xa0
[  980.954183]  fsnotify_destroy_group+0x34/0xa0
[  980.954185]  inotify_release+0x1a/0x50
[  980.954189]  __fput+0xd8/0x220
[  980.954194]  task_work_run+0x8a/0xb0
[  980.954198]  exit_to_usermode_loop+0xb9/0xc0
[  980.954200]  do_syscall_64+0x10b/0x120
[  980.954203]  entry_SYSCALL_64_after_hwframe+0x3d/0xa2
[  980.954206] RIP: 0033:0x7f031a552900
[  980.954208] RSP: 002b:00007fff93fd18b0 EFLAGS: 00000293 ORIG_RAX:
0000000000000003
[  980.954210] RAX: 0000000000000000 RBX: 0000000000000010 RCX: 00007f031a552900
[  980.954211] RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000010
[  980.954212] RBP: 00007f031beba088 R08: 0000000000000020 R09: 000055ac5a21e2ad
[  980.954213] R10: 0000000000000000 R11: 0000000000000293 R12: 0000000000000000
[  980.954214] R13: 000055ac5a488b20 R14: 000055ac5c0907f0 R15: 0000000000000000
[  980.954724] INFO: task kworker/u114:4:41909 blocked for more than
120 seconds.
[  980.954725]       Tainted: G           OE   4.14.67-solidfire1 #1
[  980.954726] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs"
disables this message.
[  980.954727] kworker/u114:4  D    0 41909      2 0x80000000
[  980.954733] Workqueue: events_unbound fsnotify_mark_destroy_workfn
[  980.954734] Call Trace:
[  980.954739]  ? __schedule+0x27f/0x870
[  980.954741]  schedule+0x28/0x80
[  980.954743]  schedule_timeout+0x1e7/0x340
[  980.954746]  ? __switch_to_asm+0x40/0x70
[  980.954747]  ? update_curr+0xe1/0x1a0
[  980.954750]  ? wait_for_completion+0xb0/0x120
[  980.954751]  wait_for_completion+0xb0/0x120
[  980.954753]  ? wake_up_q+0x70/0x70
[  980.954758]  __synchronize_srcu.part.13+0x76/0x90
[  980.954761]  ? trace_raw_output_rcu_utilization+0x40/0x40
[  980.954762]  ? try_to_wake_up+0x44/0x460
[  980.954765]  ? fsnotify_mark_destroy_workfn+0x67/0xb0
[  980.954767]  fsnotify_mark_destroy_workfn+0x67/0xb0
[  980.954769]  process_one_work+0x1da/0x3d0
[  980.954772]  worker_thread+0x21f/0x3f0
[  980.954775]  ? process_one_work+0x3d0/0x3d0
[  980.954777]  kthread+0x119/0x130
[  980.954779]  ? kthread_create_on_node+0x40/0x40
[  980.954781]  ret_from_fork+0x35/0x40

crash> print reaper_work
$3 = {
  work = {
    data = {
      counter = -117148584927483
    },
    entry = {
      next = 0xffff95743772b770,
      prev = 0xffffa2aa800a3df8
    },
    func = 0xffffffffa8249df0
  },
  timer = {
    entry = {
      next = 0xdead000000000200,
      pprev = 0x0
    },
    expires = 4295020559,
    function = 0xffffffffa80778c0,
    data = 18446744072250514272,
    flags = 69206020
  },
  wq = 0xffff95443f011400,
  cpu = 128
}

Any input is welcome.

-- 
Sebastian Kuzminsky