RHEL6: kernel panic in nfs_async_inode_return_delegation due to delegation->inode == NULL

Issue

• We have two Linux servers with MQ managers which collect information from a shared resource with NFS4 and the servers restart unexpectedly, the only error we observe is

NFSv4 callback reply buffer overflowed!

• kernel panic with log showing "NFSv4 callback reply buffer overflowed" messages, followed by a panic in nfs_async_inode_return_delegation

NFSv4 callback reply buffer overflowed!
NFSv4 callback reply buffer overflowed!
NFSv4 callback reply buffer overflowed!
BUG: unable to handle kernel NULL pointer dereference at 0000000000000000
IP: [<ffffffffa02be11e>] nfs_async_inode_return_delegation+0x3e/0x80 [nfs]
...
Pid: 2182, comm: nfsv4.0-svc Not tainted 2.6.32-358.el6.x86_64 #1 VMware, Inc. VMware Virtual Platform/440BX Desktop Reference Platform
RIP: 0010:[<ffffffffa02be11e>]  [<ffffffffa02be11e>] nfs_async_inode_return_delegation+0x3e/0x80 [nfs]
...
RAX: 0000000000000000 RBX: ffff8804992a5540 RCX: 0000000000000000
...
Process nfsv4.0-svc (pid: 2182, threadinfo ffff8806a70ba000, task ffff8806b1cc3500)
Stack:
 0000000000000000 ffff8806b322c800 ffff8806a70bbd00 ffffffffa02c2a1f
<d> ffff8806a70bbd00 ffffffffa02c1024 ffff8806a70bbd00 0000000000000000
<d> 0000000000000000 0000000000000000 ffff8806a70bbe10 ffffffffa02c1542
Call Trace:
 [<ffffffffa02c2a1f>] nfs4_callback_recall+0x5f/0xf0 [nfs]
 [<ffffffffa02c1024>] ? decode_recall_args+0x64/0xb0 [nfs]
 [<ffffffffa02c1542>] nfs4_callback_compound+0x392/0x5c0 [nfs]
 [<ffffffffa01f874d>] svc_process_common+0x56d/0x640 [sunrpc]
 [<ffffffff81063310>] ? default_wake_function+0x0/0x20
 [<ffffffffa01f8b60>] svc_process+0x110/0x160 [sunrpc]
 [<ffffffffa02c038b>] nfs4_callback_svc+0x5b/0xb0 [nfs]
 [<ffffffffa02c0330>] ? nfs4_callback_svc+0x0/0xb0 [nfs]
 [<ffffffff81096916>] kthread+0x96/0xa0
 [<ffffffff8100c0ca>] child_rip+0xa/0x20
 [<ffffffff81096880>] ? kthread+0x0/0xa0
 [<ffffffff8100c0c0>] ? child_rip+0x0/0x20
Code: 48 8b 5f c0 48 8b 00 00 00 00 00 00 00 df 4c 8b 20 49 8b 84 24 b8 02 00 00 ff 50 10 89 c2 b8 fe ff ff ff 85 d2 74 2f 48 8b 43 18 <48> 8b 80 08 01 00 00 48 8b 80 90 02 00 00 48 8b 00 f0 80 4b 48
RIP  [<ffffffffa02be11e>] nfs_async_inode_return_delegation+0x3e/0x80 [nfs]
 RSP <ffff8806a70bbcb0>
CR2: 0000000000000000