"khungtaskd" triggered kernel panic when a process vforked and it's child process does not exit nor execute any binary.

Solution Unverified - Updated -

Issue

  • Kernel panic with following call traces.
INFO: task make:27394 blocked for more than 120 seconds.
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
make          D ffffffff80156347     0 27394   9977 27420               (NOTLB)
 ffff8101df191e78 0000000000000082 000000000000ffff 0000000000000000
 0000000000000000 0000000000000009 ffff810350f70080 ffff8101b3d3a0c0
 00027183e71c0454 000000000001d5cb ffff810350f70268 0000000900000000
Call Trace:
 [<ffffffff800a0e11>] attach_pid+0x7c/0xa9
 [<ffffffff8008e81d>] enqueue_task+0x41/0x56
 [<ffffffff80063171>] wait_for_completion+0x79/0xa2
 [<ffffffff8008ee72>] default_wake_function+0x0/0xe
 [<ffffffff800310ae>] do_fork+0x17e/0x1c1
 [<ffffffff8005d28d>] tracesys+0xd5/0xe0
 [<ffffffff8005d427>] ptregscall_common+0x67/0xac

Kernel panic - not syncing: hung_task: blocked tasks
  • Traces from an another core 
PID: 6040   TASK: ffff88071ec42aa0  CPU: 0   COMMAND: "ksh"
 #0 [ffff880c69315c60] schedule at ffffffff81527bd2
 #1 [ffff880c69315d28] schedule_timeout at ffffffff81528ac5
 #2 [ffff880c69315dd8] wait_for_common at ffffffff81528743
 #3 [ffff880c69315e68] wait_for_completion at ffffffff8152885d
 #4 [ffff880c69315e78] do_fork at ffffffff81070f49
 #5 [ffff880c69315f38] sys_vfork at ffffffff81015e75
 #6 [ffff880c69315f48] stub_vfork at ffffffff8100b3d3
    RIP: 00007f8d613cce74  RSP: 00007fff5d0907c0  RFLAGS: 00000246
    RAX: 000000000000003a  RBX: 0000000000000000  RCX: ffffffffffffffff
    RDX: 0000000080000000  RSI: 0000000000000000  RDI: 0000000000498c61
    RBP: 00007fff5d090810   R8: 0000000000000001   R9: 000000000000007f
    R10: 0000000000000008  R11: 0000000000000246  R12: 0000000000f73240
    R13: 0000000000f734a8  R14: 0000000000000001  R15: 0000000000f732c8
    ORIG_RAX: 000000000000003a  CS: 0033  SS: 002b

Environment

  • Red Hat Enterprise Linux 5
  • Red Hat Enterprise Linux 6
  • khungtaskd
  • vfork(2) System Call

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