RHEL6: Crash with cifs in function find_writable_file or cifs_reopen_file

Issue

• System using cifs crashed in find_writable_file or cifs_reopen_file.

<4>general protection fault: 0000 [#1] SMP
<4>Pid: 585, comm: bdi-default Not tainted 2.6.32-642.15.1.el6.x86_64 #1 Dell Inc. PowerEdge R730/0H21J3
<4>RIP: 0010:[<ffffffffa05ad22c>]  [<ffffffffa05ad22c>] find_writable_file+0x17c/0x200 [cifs]
<4>RAX: dead000000200200 RBX: ffff8874810812e0 RCX: 00000000fffffffe
<4>RDX: dead000000100100 RSI: ffff8877bd6d9380 RDI: ffff888022ff31d0
<4>RBP: ffff884025bffb20 R08: 0000000000000000 R09: 00000000ffffffff
<4>R10: 00007842ce56a67a R11: 0000000000000000 R12: 0000000000000000
<4>R13: 0000000000000000 R14: ffff888022ff31c0 R15: ffff884025bf7520
<4>Process bdi-default (pid: 585, threadinfo ffff884025bfc000, task ffff884025bf7520)
<4>Stack:
<4> ffff884025bf7520 ffffffffa05d6194 ffffffff00000001 ffff8874810812f0
<4><d> 000000000000005f ffff887167df5a00 ffff887481081448 ffff884025bffd40
<4><d> 0000000000000010 0000000000000010 ffff884025bffbe0 ffffffffa05ae0c4

BUG: unable to handle kernel NULL pointer dereference at 0000000000000108
RIP: 0010:[<ffffffffa02ffe4c>]  [<ffffffffa02ffe4c>] cifs_reopen_file+0x9c/0x480 [cifs]
RSP: 0018:ffff8806360d3a20  EFLAGS: 00010202
RAX: 0000000000000000 RBX: ffff880630ecd580 RCX: ffff8806360c4ab0
RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffff88020382f500
RBP: ffff8806360d3ac0 R08: 0000000000000002 R09: ffffffffa0329c34
R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
R13: 0000000000000000 R14: ffff880630ecd600 R15: 0000000000842324
Process bdi-default (pid: 41, threadinfo ffff8806360d0000, task ffff8806360c4ab0)
Stack:
 ffff8806360d3a50 ffffffff812903a5 ffff8806360d3a50 ffffffff81a863c0
<d> ffff88020382f500 ffff880630ecd580 ffff8802b635f400 ffff880630ecd5e8
<d> ffff880630ecd5e8 ffff880630ecd5e8 00ff8806360d3ac0 ffffffffa02ff7a2