linux-kernel - process 'stuck' at exit.

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Date:	Tue, 10 Dec 2013 10:47:24 -0500
From:	Dave Jones <davej@...hat.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Linux Kernel <linux-kernel@...r.kernel.org>
Subject: process 'stuck' at exit.

I woke up to find my fuzzer in a curious state.

 1121 pts/5    SN+    0:00  |       \_ ../trinity -q -l off -N 999999 -C 42
 1130 pts/5    SN+    0:01  |           \_ ../trinity -q -l off -N 999999 -C 42
 1131 pts/5    SN+    0:17  |           \_ ../trinity -q -l off -N 999999 -C 42
10818 ?        RNs  21115152:53  |               \_ ../trinity -q -l off -N 999999 -C 42

(ignore the first 3 pids, they're waiting on 10818, which is the interesting one)

It's completed its run of 999999 syscalls, and looking at tmux, it tried to exit.

/proc/10818/stack just shows

[<ffffffffffffffff>] 0xffffffffffffffff

Top reports a core is spinning in the kernel 100%, so I ran perf top -a
and saw..

  8.63%  [kernel]                [k] trace_hardirqs_off_caller
  7.68%  [kernel]                [k] __lock_acquire
  5.35%  [kernel]                [k] gup_huge_pmd
  5.31%  [kernel]                [k] put_compound_page
  4.93%  [kernel]                [k] gup_pud_range
  4.76%  [kernel]                [k] trace_hardirqs_on_caller
  4.58%  [kernel]                [k] get_user_pages_fast
  4.00%  [kernel]                [k] debug_smp_processor_id
  4.00%  [kernel]                [k] lock_is_held
  3.73%  [kernel]                [k] lock_acquired
  3.67%  [kernel]                [k] lock_release


sysrq-t shows..

trinity-child27 R  running task     5520 10818   1131 0x00080004
 0000000000000000 ffff8801b0ef4170 000000000000032c ffff8801b609e108
 0000000000000000 ffff880160d21c30 ffffffff810ad895 ffffffff817587a0
 ffff8801b0ef4170 ffff8801b609e0a8 ffff8801b609e000 ffff880160d21d50
Call Trace:
 [<ffffffff817587a0>] ? retint_restore_args+0xe/0xe
 [<ffffffff8132af0e>] ? trace_hardirqs_on_thunk+0x3a/0x3f
 [<ffffffff8100b184>] ? native_sched_clock+0x24/0x80
 [<ffffffff8109624f>] ? local_clock+0xf/0x50
 [<ffffffff810aa27e>] ? put_lock_stats.isra.28+0xe/0x30
 [<ffffffff8103edd0>] ? gup_pud_range+0x170/0x190
 [<ffffffff8103f0d5>] ? get_user_pages_fast+0x1a5/0x1c0
 [<ffffffff810ad1f5>] ? trace_hardirqs_on_caller+0x115/0x1e0
 [<ffffffff810a8a2f>] ? up_read+0x1f/0x40
 [<ffffffff8103f0d5>] ? get_user_pages_fast+0x1a5/0x1c0
 [<ffffffff8115f76c>] ? put_page+0x3c/0x50
 [<ffffffff810dd525>] ? get_futex_key+0xd5/0x2c0
 [<ffffffff810df18a>] ? futex_requeue+0xfa/0x9c0
 [<ffffffff810e019e>] ? do_futex+0xae/0xc80
 [<ffffffff810aa27e>] ? put_lock_stats.isra.28+0xe/0x30
 [<ffffffff810aa7de>] ? lock_release_holdtime.part.29+0xee/0x170
 [<ffffffff8114f16e>] ? context_tracking_user_exit+0x4e/0x190
 [<ffffffff810ad1f5>] ? trace_hardirqs_on_caller+0x115/0x1e0
 [<ffffffff810e0de1>] ? SyS_futex+0x71/0x150
 [<ffffffff81010a45>] ? syscall_trace_enter+0x145/0x2a0
 [<ffffffff81760be4>] ? tracesys+0xdd/0xe2


any ideas ?

	Dave

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