in my fstab file have this line:
192.168.1.202:/share/smb	/home/qiao/202	nfs	defaults	0 0

and server is CentOS 5.7, samba-3.0.33-3.29.el5_6.2

Looking at upstream v3.7.2, not the Fedora source, but I suspect the line numbers are the same, in which case this is:

  BUG_ON(!list_empty(&serv->sv_tempsocks));

which looks similar to the problem reported in http://mid.gmane.org/<50F42F85.50907>.

Bruce, please have a look at "SUNRPC: protect transport processing with rw sem" patch in NFS mailing list.
This one is marked with RFC, because the solution is rough. But it seems much more simple and safe, then playing with transports bits, etc.

I get a similar problem, but get a mount.nfs tainted message.
This started to happen after I switched from NFS4 to NFS3 to avoid kernel BUG at net/sunrpc/svc_xprt.c:921!

I'm mounting a RHEL Release 6.2



kernel BUG at net/sunrpc/svc.c:559!
invalid opcode: 0000 [#2] SMP 
Modules linked in: fuse nfsv3 nfs_acl nfsv4 auth_rpcgss nfs dns_resolver fscache ip6table_filter ip6_tables ebtable_nat ebtables ipt_MASQUERADE iptable_nat nf_nat_ipv4 nf_nat nf_conntrack_ipv4 nf_defrag_ipv4 xt_state nf_conntrack xt_CHECKSUM iptable_mangle bridge st
p llc lockd sunrpc rfcomm bnep be2iscsi iscsi_boot_sysfs bnx2i cnic uio cxgb4i cxgb4 cxgb3i cxgb3 mdio libcxgbi ib_iser rdma_cm ib_addr iw_cm ib_cm ib_sa ib_
mad ib_core iscsi_tcp libiscsi_tcp libiscsi scsi_transport_iscsi snd_hda_codec_analog snd_hda_intel snd_hda_codec btusb snd_hwdep snd_seq bluetooth snd_seq_d
evice snd_pcm rfkill snd_page_alloc snd_timer snd coretemp soundcore mei iTCO_wdt iTCO_vendor_support i2c_i801 lpc_ich dell_wmi dcdbas mfd_core serio_raw spa
rse_keymap e1000e microcode vhost_net tun macvtap macvlan kvm_intel kvm binfmt_misc uinput ata_generic pata_acpi wmi i915 video i2c_algo_bit drm_kms_helper d
rm i2c_core
CPU 0 
Pid: 26429, comm: mount.nfs Tainted: G      D      3.7.3-101.fc17.x86_64 #1 Dell Inc. OptiPlex 780           
      /0DFRFW
 RIP: 0010:[<ffffffffa04e5362>]  [<ffffffffa04e5362>] svc_destroy+0x132/0x140 [sunrpc]
 RSP: 0018:ffff88010f023888  EFLAGS: 00010202
 RAX: ffff8800b486ba38 RBX: ffff8800b486ba00 RCX: 0000000000000069
 RDX: ffff880111ee15c8 RSI: 0000000000000286 RDI: 0000000000000286
 RBP: ffff88010f023898 R08: dead000000200200 R09: ffff880117beafa0
 R10: 00000000000000e0 R11: 0000000000000000 R12: ffff8801033de000
 R13: ffff880069daff00 R14: ffff8800b486ba00 R15: ffff88010f023ae0
 FS:  00007f8f20514840(0000) GS:ffff880117c00000(0000) knlGS:0000000000000000
 CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
 CR2: 00007f8f1fbb16f5 CR3: 0000000110666000 CR4: 00000000000407f0
 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
 DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
 Process mount.nfs (pid: 26429, threadinfo ffff88010f022000, task ffff880013862e40)
 Stack:
  ffff8800b486ba00 ffff880069daff04 ffff88010f0238c8 ffffffffa04e5776
  0000000000000000 0000000000000000 ffffffff81ca3980 ffff88010cffb800
  ffff88010f0238f8 ffffffffa062e063 0000000000000000 ffff88001ab22c00
 Call Trace:
  [<ffffffffa04e5776>] svc_exit_thread+0xa6/0xb0 [sunrpc]
  [<ffffffffa062e063>] nfs_callback_down+0x73/0xe0 [nfsv4]
  [<ffffffffa0631619>] nfs4_free_client+0x59/0xc0 [nfsv4]
  [<ffffffffa05cad2b>] nfs_put_client+0xeb/0x110 [nfs]
  [<ffffffffa063181e>] nfs4_init_client+0x19e/0x2e0 [nfsv4]
  [<ffffffff812e64bf>] ? idr_get_new_above_int+0x3f/0x50
  [<ffffffffa04e2fe4>] ? rpc_init_wait_queue+0x64/0xa0 [sunrpc]
  [<ffffffffa06314f9>] ? nfs4_alloc_client+0xf9/0x1c0 [nfsv4]
  [<ffffffffa05cb229>] nfs_get_client+0x299/0x350 [nfs]
  [<ffffffffa0631378>] nfs4_set_client.isra.5+0x78/0x100 [nfsv4]
  [<ffffffffa063220c>] nfs4_create_server+0xec/0x390 [nfsv4]
  [<ffffffffa062af59>] nfs4_remote_mount+0x39/0x70 [nfsv4]
  [<ffffffff81198443>] mount_fs+0x43/0x1b0
  [<ffffffff811519d0>] ? __alloc_percpu+0x10/0x20
  [<ffffffff811b171f>] vfs_kern_mount+0x6f/0x100
  [<ffffffffa062aed1>] nfs_do_root_mount+0x91/0xe0 [nfsv4]
  [<ffffffffa062b244>] nfs4_try_mount+0x44/0xc0 [nfsv4]
  [<ffffffffa05cc340>] ? get_nfs_version+0x30/0x90 [nfs]
  [<ffffffffa05d71a5>] nfs_fs_mount+0x265/0xcf0 [nfs]
  [<ffffffffa05d7d80>] ? nfs_clone_super+0x150/0x150 [nfs]
  [<ffffffffa05d4940>] ? nfs_clone_sb_security+0x60/0x60 [nfs]
  [<ffffffff81198443>] mount_fs+0x43/0x1b0
  [<ffffffff811519d0>] ? __alloc_percpu+0x10/0x20
  [<ffffffff811b171f>] vfs_kern_mount+0x6f/0x100
  [<ffffffff811b2194>] do_kern_mount+0x54/0x110
  [<ffffffff811b3cf5>] do_mount+0x315/0x8e0
  [<ffffffff811b384a>] ? copy_mount_options+0x3a/0x180
  [<ffffffff811b434e>] sys_mount+0x8e/0xe0
  [<ffffffff81639799>] system_call_fastpath+0x16/0x1b
 Code: 4f a0 31 c0 e8 32 1d 14 e1 e9 22 ff ff ff 48 8b 07 8b 57 14 48 c7 c7 c7 ab 4f a0 48 8b 70 20 31 c0 e8 1
5 1d 14 e1 e9 ec fe ff ff <0f> 0b 0f 0b 66 2e 0f 1f 84 00 00 00 00 00 66 66 66 66 90 55 48 
 RIP  [<ffffffffa04e5362>] svc_destroy+0x132/0x140 [sunrpc]
RSP <ffff88010f023888>

You can try these patches:
http://www.spinics.net/lists/linux-nfs/msg35363.html
http://www.spinics.net/lists/linux-nfs/msg35364.html

*** Bug 910457 has been marked as a duplicate of this bug. ***

Just wanted to note that I just now saw this (or, more correctly, the "kernel BUG at net/sunrpc/svc_xprt.c:921" backtrace I reported in one of the duplicated) on F17 with 3.7.9-104.fc17.x86_64.  I had not previously seen this issue on F17.

(In reply to comment #7)
> Just wanted to note that I just now saw this (or, more correctly, the
> "kernel BUG at net/sunrpc/svc_xprt.c:921" backtrace I reported in one of the
> duplicated) on F17 with 3.7.9-104.fc17.x86_64.  I had not previously seen
> this issue on F17.

This is a race. I.e. it doesn't happen on every run.
So it's ok.
And wanna note, that the patches, fixing the problem, wasn't yet included into stable branch.

Yeah, I know.  Unfortunately I don't think the patches even got much of a review, or at least if they did I was dropped from the CC list.  They're certainly not in Linus's tree.  I would petition for them to get into Fedora's kernel but without any indication of movement towards upstream acceptance I don't think they'd agree.  I'd really rather not have to roll out a custom kernel across all of my desktops, but I'm not sure what other option I have at this point; even a rare bug happens pretty commonly when you get up over a hundred desktops.

The patches are in maintaners's tree and will become a part of 3.9 kernel.
Also, they are requested to be included into stable kernels.
Once they will be accepted by Greg, I (or Bruce) will inform you about stable kernel version you can use.

They're in Linus' tree as of this morning.  Fedora can carry them as patches until they work into 3.8.y.

Applied to both F17 and F18.

kernel-3.8.2-105.fc17 has been submitted as an update for Fedora 17.
https://admin.fedoraproject.org/updates/kernel-3.8.2-105.fc17

Package kernel-3.8.2-105.fc17:
* should fix your issue,
* was pushed to the Fedora 17 testing repository,
* should be available at your local mirror within two days.
Update it with:
# su -c 'yum update --enablerepo=updates-testing kernel-3.8.2-105.fc17'
as soon as you are able to, then reboot.
Please go to the following url:
https://admin.fedoraproject.org/updates/FEDORA-2013-3638/kernel-3.8.2-105.fc17
then log in and leave karma (feedback).

*** Bug 921062 has been marked as a duplicate of this bug. ***

kernel-3.8.2-105.fc17 has been submitted as an update for Fedora 17.
https://admin.fedoraproject.org/updates/FEDORA-2013-3638/kernel-3.8.2-105.fc17

kernel-3.8.3-101.fc17 has been submitted as an update for Fedora 17.
https://admin.fedoraproject.org/updates/kernel-3.8.3-101.fc17

Package kernel-3.8.3-101.fc17:
* should fix your issue,
* was pushed to the Fedora 17 testing repository,
* should be available at your local mirror within two days.
Update it with:
# su -c 'yum update --enablerepo=updates-testing kernel-3.8.3-101.fc17'
as soon as you are able to, then reboot.
Please go to the following url:
https://admin.fedoraproject.org/updates/FEDORA-2013-3909/kernel-3.8.3-101.fc17
then log in and leave karma (feedback).

kernel-3.8.3-103.fc17 has been pushed to the Fedora 17 stable repository.  If problems still persist, please make note of it in this bug report.