abrt version: 2.0.1
architecture:   x86_64
cmdline:        ro root=/dev/mapper/vg_phx6-lv_root rd_LVM_LV=vg_phx6/lv_root rd_LVM_LV=vg_phx6/lv_swap rd_NO_LUKS rd_NO_MD rd_NO_DM LANG=en_US.UTF-8 SYSFONT=latarcyrheb-sun16 KEYTABLE=us rhgb quiet
component:      kernel
kernel:         2.6.38.8-32.fc15.x86_64
kernel_tainted: 128
os_release:     Fedora release 15 (Lovelock)
package:        kernel
reason:         BUG: Dentry ffff880040a5d480{i=2,n=} still in use (1) [unmount of nfs 0:2c]
time:           Wed Jun 22 21:16:18 2011

backtrace:
:BUG: Dentry ffff880040a5d480{i=2,n=} still in use (1) [unmount of nfs 0:2c]
:------------[ cut here ]------------
:kernel BUG at fs/dcache.c:947!
:invalid opcode: 0000 [#1] SMP 
:last sysfs file: /sys/devices/system/cpu/cpu5/cache/index2/shared_cpu_map
:CPU 1 
:Modules linked in: tcp_lp nfs lockd fscache nfs_acl auth_rpcgss fuse vboxnetadp vboxnetflt sunrpc vboxdrv cpufreq_ondemand powernow_k8 freq_table mperf ip6t_REJECT nf_conntrack_ipv6 nf_defrag_ipv6 ip6table_filter ip6_tables wacom joydev snd_hda_codec_hdmi snd_hda_codec_realtek snd_hda_intel snd_hda_codec snd_hwdep snd_seq snd_seq_device snd_pcm microcode edac_core serio_raw snd_timer edac_mce_amd k10temp snd soundcore snd_page_alloc sp5100_tco i2c_piix4 shpchp wmi xhci_hcd r8169 mii ipv6 pata_acpi ata_generic firewire_ohci firewire_core pata_jmicron crc_itu_t pata_atiixp radeon ttm drm_kms_helper drm i2c_algo_bit i2c_core [last unloaded: scsi_wait_scan]
:Pid: 6063, comm: umount.nfs Not tainted 2.6.38.8-32.fc15.x86_64 #1 Gigabyte Technology Co., Ltd. GA-890GPA-UD3H/GA-890GPA-UD3H
:RIP: 0010:[<ffffffff811328ff>]  [<ffffffff811328ff>] shrink_dcache_for_umount_subtree+0x104/0x1c9
:RSP: 0018:ffff8800600f7d98  EFLAGS: 00010296
:RAX: 0000000000000061 RBX: ffff880040a5d480 RCX: 000000000000c1b8
:RDX: 0000000000000000 RSI: 0000000000000046 RDI: 0000000000000246
:RBP: ffff8800600f7dc8 R08: 0000000000000002 R09: 0000ffff00066c0a
:R10: 0000ffff00066c0a R11: 0000000000000003 R12: ffff880040a5d480
:R13: ffff8800895f9a80 R14: ffff880040a5d230 R15: 0000000000000000
:FS:  00007f70a99e2720(0000) GS:ffff8800cfa40000(0000) knlGS:00000000f40678a0
:CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
:CR2: 00007fa647bac000 CR3: 00000000ba4d2000 CR4: 00000000000006e0
:DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
:DR3: 0000000000000000 DR6: 00000000ffff4ff0 DR7: 0000000000000400
:Process umount.nfs (pid: 6063, threadinfo ffff8800600f6000, task ffff880004cc5cc0)
:Stack:
: ffff880007f2c658 0000000000000000 ffff880007f2c400 ffff880040a5db40
: ffff8800600f7f28 ffff880040a5d180 ffff8800600f7de8 ffffffff81133271
: ffff880007f2c400 ffffffffa059a090 ffff8800600f7e18 ffffffff81122e49
:Call Trace:
: [<ffffffff81133271>] shrink_dcache_for_umount+0x4d/0x5f
: [<ffffffff81122e49>] generic_shutdown_super+0x23/0xde
: [<ffffffff81122f81>] kill_anon_super+0x13/0x4c
: [<ffffffffa0574198>] nfs_kill_super+0x1b/0x30 [nfs]
: [<ffffffff811231a5>] deactivate_locked_super+0x26/0x4b
: [<ffffffff81123d0e>] deactivate_super+0x37/0x3b
: [<ffffffff8113863c>] mntput_no_expire+0xcc/0xd1
: [<ffffffff81138667>] mntput+0x26/0x28
: [<ffffffff81138aee>] release_mounts+0x59/0x73
: [<ffffffff81139054>] sys_umount+0x28d/0x2da
: [<ffffffff81009bc2>] system_call_fastpath+0x16/0x1b
:Code: 8b 40 28 4c 8b 08 48 8b 43 30 48 85 c0 74 07 48 8b 90 a8 00 00 00 48 89 34 24 48 c7 c7 2c 2a 7b 81 48 89 de 31 c0 e8 f2 9e 33 00 <0f> 0b 4c 8b 63 18 4c 39 e3 75 11 48 8d bb 90 00 00 00 45 31 e4 
:RIP  [<ffffffff811328ff>] shrink_dcache_for_umount_subtree+0x104/0x1c9
: RSP <ffff8800600f7d98>

comment:
:Nothing releted to nfs. Just browsed the Web. Screen blanked for a few seconds than returned with ABRT messge.
:
:nfs was mounted with autofs. Nautilus was opened on backround but showed local directory.