kernel panic when mount NFSv4

[Mi Jinlong <mijinlong@cn.fujitsu.com>]

Hi,

When testing NFSv4 at RHEL6 with kernel 2.6.32, I got a kernel panic
at NFS client's __rpc_create_common function.

The panic place is:
  rpc_mkpipe
    __rpc_lookup_create()          <=== find pipefile *idmap*
    __rpc_mkpipe()                 <=== pipefile is *idmap*
      __rpc_create_common()
       ******  BUG_ON(!d_unhashed(dentry)); ******    *panic*

It means that the dentry's d_flags have be set DCACHE_UNHASHED, 
but it should not be set here.

Is someone known this bug? or give me some idea?

A reproduce program is append, but it can't reproduce the bug every time.
the export is: "/nfsroot       *(rw,no_root_squash,fsid=0,insecure)"

And the panic message is append.

============================================================================
#!/bin/sh

LOOPTOTAL=768
LOOPCOUNT=0
ret=0

while [ $LOOPCOUNT -ne $LOOPTOTAL ]
do
	((LOOPCOUNT += 1))
	service nfs restart
	/usr/sbin/rpc.idmapd
	mount -t nfs4 127.0.0.1:/ /mnt|| return 1;
	ls -l /var/lib/nfs/rpc_pipefs/nfs/*/
	umount /mnt
	echo $LOOPCOUNT
done

===============================================================================
Code: af 60 01 00 00 89 fa 89 f0 e8 64 cf 89 f0 e8 5c 7c 64 cf 31 c0 8b 5c 24 10 8b 
74 24 14 8b 7c 24 18 8b 6c 24 1c 83 c4 20 c3 <0f> 0b eb fc 8b 46 28 c7 44 24 08 20
de ee f0 c7 44 24 04 56 ea 
EIP:[<f0ee92ea>] __rpc_create_common+0x8a/0xc0 [sunrpc] SS:ESP 0068:eccb5d28
---[ end trace 8f5606cd08928ed2]---
Kernel panic - not syncing: Fatal exception
Pid:7131, comm: mount.nfs4 Tainted: G     D   -------------------2.6.32 #1
Call Trace:
 [<c080ad18>] ? panic+0x42/0xed
 [<c080e42c>] ? oops_end+0xbc/0xd0
 [<c040b090>] ? do_invalid_op+0x0/0x90
 [<c040b10f>] ? do_invalid_op+0x7f/0x90
 [<f0ee92ea>] ? __rpc_create_common+0x8a/0xc0[sunrpc]
 [<f0edc433>] ? rpc_free_task+0x33/0x70[sunrpc]
 [<f0ed6508>] ? prc_call_sync+0x48/0x60[sunrpc]
 [<f0ed656e>] ? rpc_ping+0x4e/0x60[sunrpc]
 [<f0ed6eaf>] ? rpc_create+0x38f/0x4f0[sunrpc]
 [<c080d80b>] ? error_code+0x73/0x78
 [<f0ee92ea>] ? __rpc_create_common+0x8a/0xc0[sunrpc]
 [<c0532bda>] ? d_lookup+0x2a/0x40
 [<f0ee94b1>] ? rpc_mkpipe+0x111/0x1b0[sunrpc]
 [<f10a59f4>] ? nfs_create_rpc_client+0xb4/0xf0[nfs]
 [<f10d6c6d>] ? nfs_fscache_get_client_cookie+0x1d/0x50[nfs]
 [<f10d3fcb>] ? nfs_idmap_new+0x7b/0x140[nfs]
 [<c05e76aa>] ? strlcpy+0x3a/0x60
 [<f10a60ca>] ? nfs4_set_client+0xea/0x2b0[nfs]
 [<f10a6d0c>] ? nfs4_create_server+0xac/0x1b0[nfs]
 [<c04f1400>] ? krealloc+0x40/0x50
 [<f10b0e8b>] ? nfs4_remote_get_sb+0x6b/0x250[nfs]
 [<c04f14ec>] ? kstrdup+0x3c/0x60
 [<c0520739>] ? vfs_kern_mount+0x69/0x170
 [<f10b1a3c>] ? nfs_do_root_mount+0x6c/0xa0[nfs]
 [<f10b1b47>] ? nfs4_try_mount+0x37/0xa0[nfs]
 [<f10afe6d>] ? nfs4_validate_text_mount_data+-x7d/0xf0[nfs]
 [<f10b1c42>] ? nfs4_get_sb+0x92/0x2f0
 [<c0520739>] ? vfs_kern_mount+0x69/0x170
 [<c05366d2>] ? get_fs_type+0x32/0xb0
 [<c052089f>] ? do_kern_mount+0x3f/0xe0
 [<c053954f>] ? do_mount+0x2ef/0x740
 [<c0537740>] ? copy_mount_options+0xb0/0x120
 [<c0539a0e>] ? sys_mount+0x6e/0xa0