RHEL6.7: shutdown / reboot hangs with findmnt in a readlink system call, doing path_walk and stuck in autofs4_wait

Issue

• Why autofs causing system hangs while rebooting/shutdown ?
• From vmcore, we see that shutdown is hung with blkdeactivate calling findmnt, which gets stuck in autofs at autofs4_wait

crash> ps -p 2685
PID: 0      TASK: ffffffff81a95020  CPU: 0   COMMAND: "swapper"
 PID: 1      TASK: ffff8802bbaa1520  CPU: 1   COMMAND: "init"
  PID: 2478   TASK: ffff8802b40b2040  CPU: 1   COMMAND: "rc"
   PID: 2673   TASK: ffff8802b41f4ab0  CPU: 0   COMMAND: "K75blk-availabi"
    PID: 2676   TASK: ffff8802b4247520  CPU: 0   COMMAND: "blkdeactivate"
     PID: 2685   TASK: ffff8802b39a0ab0  CPU: 0   COMMAND: "findmnt"

PID: 2685   TASK: ffff8802b39a0ab0  CPU: 0   COMMAND: "findmnt"
 #0 [ffff8802b976fa58] schedule at ffffffff815384f0
 #1 [ffff8802b976fb30] autofs4_wait at ffffffffa01d97b5 [autofs4]
 #2 [ffff8802b976fbe0] autofs4_d_manage at ffffffffa01d7ec5 [autofs4]
 #3 [ffff8802b976fc10] follow_managed at ffffffff811a1468
 #4 [ffff8802b976fc70] do_lookup at ffffffff811a16ff
 #5 [ffff8802b976fcd0] __link_path_walk at ffffffff811a2494
 #6 [ffff8802b976fdb0] path_walk at ffffffff811a2faa
 #7 [ffff8802b976fdf0] filename_lookup at ffffffff811a31bb
 #8 [ffff8802b976fe30] user_path_at at ffffffff811a42e7
 #9 [ffff8802b976ff00] sys_readlinkat at ffffffff811972f9
#10 [ffff8802b976ff70] sys_readlink at ffffffff811973eb
#11 [ffff8802b976ff80] system_call_fastpath at ffffffff8100b0d2