Issue

• System crashed during NFS unmount in context of __fscache_disable_cookie call

[3891892.449375] FS-Cache: 
[3891892.449409] FS-Cache: Assertion failed
[3891892.449425] FS-Cache: 0 > 0 is false
[3891892.449508] ------------[ cut here ]------------
[3891892.449526] kernel BUG at fs/fscache/cookie.c:519!

crash> bt
PID: 7533   TASK: ffff880b96345e20  CPU: 4   COMMAND: "umount.nfs4"
 #0 [ffff880b9b7939c0] machine_kexec at ffffffff81059bab
 #1 [ffff880b9b793a20] __crash_kexec at ffffffff81105822
 #2 [ffff880b9b793af0] crash_kexec at ffffffff81105910
 #3 [ffff880b9b793b08] oops_end at ffffffff81690008
 #4 [ffff880b9b793b30] die at ffffffff8102e93b
 #5 [ffff880b9b793b60] do_trap at ffffffff8168f6c0
 #6 [ffff880b9b793bb0] do_invalid_op at ffffffff8102b144
 #7 [ffff880b9b793c60] invalid_op at ffffffff8169909e
    [exception RIP: __fscache_disable_cookie+456]
    RIP: ffffffffa04cd0e8  RSP: ffff880b9b793d10  RFLAGS: 00010246
    RAX: 0000000000000018  RBX: ffff880b4637d528  RCX: 0000000000000006
    RDX: 0000000000000000  RSI: 0000000000000246  RDI: ffff880c3fd0f830
    RBP: ffff880b9b793d38   R8: 0000000000000082   R9: 0000000000000b89
    R10: 0000000000000001  R11: 0000000000000000  R12: ffff880b4637d528
    R13: ffffffffa05a57c0  R14: ffff880b9b793e00  R15: ffff880c05b1bba0
    ORIG_RAX: ffffffffffffffff  CS: 0010  SS: 0018
 #8 [ffff880b9b793d40] __fscache_relinquish_cookie at ffffffffa04cd629 [fscache]
 #9 [ffff880b9b793d58] nfs_fscache_clear_inode at ffffffffa0548afb [nfs]
#10 [ffff880b9b793d78] nfs_clear_inode at ffffffffa053298f [nfs]
#11 [ffff880b9b793d90] nfs4_evict_inode at ffffffffa058b331 [nfsv4]
#12 [ffff880b9b793da8] evict at ffffffff8121aa67
#13 [ffff880b9b793dd0] dispose_list at ffffffff8121ab6e
#14 [ffff880b9b793df8] evict_inodes at ffffffff8121b7c4
#15 [ffff880b9b793e48] generic_shutdown_super at ffffffff81200ff8
#16 [ffff880b9b793e70] kill_anon_super at ffffffff812013f2
#17 [ffff880b9b793e88] nfs_kill_super at ffffffffa0537abb [nfs]
#18 [ffff880b9b793ea8] deactivate_locked_super at ffffffff812017a9
#19 [ffff880b9b793ec8] deactivate_super at ffffffff81201da6
#20 [ffff880b9b793ee0] mntput_no_expire at ffffffff8121f1e5
#21 [ffff880b9b793f08] sys_umount at ffffffff81220320
#22 [ffff880b9b793f80] system_call_fastpath at ffffffff81697809
    RIP: 00007ff5a714c807  RSP: 00007ffceb95acb8  RFLAGS: 00010206
    RAX: 00000000000000a6  RBX: ffffffff81697809  RCX: 0000000000000010
    RDX: 0000000000000001  RSI: 0000000000000000  RDI: 00007ff5a7edd4e0
    RBP: 00007ff5a7edd4e0   R8: 61735f7472697673   R9: 69665f786f62646e
    R10: 00007ffceb95a9a0  R11: 0000000000000246  R12: 00007ffceb95c84f
    R13: 00007ff5a7eddea0  R14: 0000000000000000  R15: 00007ff5a7655d38
    ORIG_RAX: 00000000000000a6  CS: 0033  SS: 002b