RHEL7 の shrink_dcache_for_umount_subtree() が原因で、NFS4 クライアントでカーネルパニックが発生し、BUG: Dentry still in use エラーが出力される

Issue

• メンテナンススロット時に、4 つのノードが同じようにクラッシュしました。毎回、動的ライブラリがクラッシュの原因になります。
• NFS4 ファイルシステムのマウントを解除するとシステムがクラッシュし、Dentry ... still in use (1) [unmount of nfs4 ...] エラーが出力されます。

[4319532.467882] BUG:Dentry ffff881020a740c0{i=138c0b,n=libsvml.so} still in use (1) [unmount of nfs4 0:43]
[4319532.477457] ------------[ cut here ]------------
[4319532.482241] kernel BUG at fs/dcache.c:945!
...

PID:51770 TASK: ffff881ef40f2d80 CPU:49 COMMAND:"umount.nfs4"
 #0 [ffff880da106fad8] machine_kexec at ffffffff8104c4cb
 #1 [ffff880da106fb38] crash_kexec at ffffffff810e1fe2
 #2 [ffff880da106fc08] oops_end at ffffffff8160c588
 #3 [ffff880da106fc30] die at ffffffff8101736b
 #4 [ffff880da106fc60] do_trap at ffffffff8160bc60
 #5 [ffff880da106fcb0] do_invalid_op at ffffffff810141c4
 #6 [ffff880da106fd60] invalid_op at ffffffff816154de
    [exception RIP: shrink_dcache_for_umount_subtree+428]
    RIP: ffffffff811dd56c RSP: ffff880da106fe10 RFLAGS:00010246
    RAX:000000000000005b RBX: ffff881020a740c0 RCX:0000000000000000
    RDX:0000000000000000 RSI: ffff88203f22d488 RDI:0000000000000246
    RBP: ffff880da106fe28 R8:0000000000000096 R9:00000000000049b3
    R10:0000000000000000 R11: ffff880da106fb26 R12: ffff880fa9aec780
    R13: ffffffffa0dbb7a0 R14: ffff8810199e6f40 R15: ffff8810199e6f20
    ORIG_RAX: ffffffffffffffff CS:0010 SS:0018
 #7 [ffff880da106fe30] shrink_dcache_for_umount at ffffffff811df109
 #8 [ffff880da106fe48] generic_shutdown_super at ffffffff811c8901
 #9 [ffff880da106fe70] kill_anon_super at ffffffff811c8ba2
#10 [ffff880da106fe88] nfs_kill_super at ffffffffa0d5726b [nfs]
#11 [ffff880da106fea8] deactivate_locked_super at ffffffff811c8f4d
#12 [ffff880da106fec8] deactivate_super at ffffffff811c9556
#13 [ffff880da106fee0] mntput_no_expire at ffffffff811e6265
#14 [ffff880da106ff08] sys_umount at ffffffff811e739f
#15 [ffff880da106ff80] system_call_fastpath at ffffffff81613da9
    RIP:00007fe5071a9247 RSP:00007fff94139148 RFLAGS:00010246
    RAX:00000000000000a6 RBX: ffffffff81613da9 RCX:0000000000000000
    RDX:0000000000000001 RSI:0000000000000001 RDI:00007fe50818f080
    RBP:00007fe50818f080 R8:6e65696c632c3738 R9:33313d7264646174
    R10:00007fff94138e30 R11:0000000000000202 R12:00007fff9413af90
    R13:00007fe50818ef10 R14:0000000000000001 R15:00007fe5076b2d38
    ORIG_RAX:00000000000000a6 CS:0033 SS:002b