Description of problem:
I was working with a flash drive at the time.

Additional info:
reporter:       libreport-2.2.2
BUG: soft lockup - CPU#2 stuck for 22s! [systemd-udevd:29833]
Modules linked in: isofs des_generic md4 nls_utf8 cifs rpcsec_gss_krb5 auth_rpcgss nfsv4 dns_resolver nfs lockd fscache bnep bluetooth fuse xt_CHECKSUM ipt_MASQUERADE ip6t_rpfilter ip6t_REJECT xt_conntrack cfg80211 ebtable_nat ebtable_broute bridge stp llc ebtable_filter ebtables ip6table_nat nf_conntrack_ipv6 nf_defrag_ipv6 nf_nat_ipv6 ip6table_mangle ip6table_security ip6table_raw ip6table_filter ip6_tables iptable_nat nf_conntrack_ipv4 nf_defrag_ipv4 nf_nat_ipv4 nf_nat nf_conntrack iptable_mangle iptable_security iptable_raw s5h1411 cx25840 cx23885 btcx_risc altera_ci videobuf_dvb tda18271 altera_stapl tveeprom cx2341x videobuf_dma_sg videobuf_core dvb_core ums_realtek uas snd_hda_codec_hdmi joydev snd_hda_codec_realtek snd_hda_codec_generic snd_usb_audio snd_hda_intel snd_hda_controller snd_usbmidi_lib rc_core usb_storage ftdi_sio snd_hda_codec usblp eeepc_wmi v4l2_common snd_virtuoso asus_wmi snd_oxygen_lib videodev snd_hwdep sparse_keymap iTCO_wdt iTCO_vendor_support media snd_seq rfkill snd_mpu401_uart snd_rawmidi snd_seq_device snd_pcm snd_timer r8169 snd mei_me soundcore x86_pkg_temp_thermal mei mii shpchp lpc_ich mfd_core coretemp serio_raw i2c_i801 kvm_intel kvm crct10dif_pclmul crc32_pclmul crc32c_intel ghash_clmulni_intel microcode sunrpc binfmt_misc nouveau i2c_algo_bit drm_kms_helper ttm mxm_wmi drm i2c_core video wmi
CPU: 2 PID: 29833 Comm: systemd-udevd Not tainted 3.15.0-0.rc6.git0.1.fc21.x86_64 #1
Hardware name: System manufacturer System Product Name/P8Z77-V LE PLUS, BIOS 0908 12/10/2013
task: ffff8807c61bf5c0 ti: ffff8807c94a2000 task.ti: ffff8807c94a2000
RIP: 0010:[<ffffffff81205d3b>]  [<ffffffff81205d3b>] d_shrink_add+0xb/0x70
RSP: 0018:ffff8807c94a3bc0  EFLAGS: 00000246
RAX: ffff88077bb89600 RBX: 000000001f8b1f8a RCX: 0000000028032802
RDX: 000000006032602e RSI: ffff8807c94a3c10 RDI: ffff88077bb89600
RBP: ffff8807c94a3bc8 R08: ffff88077bb89680 R09: 0000000180240020
R10: ffff88081ec98150 R11: ffff88075a4a2ee0 R12: ffff880748e80b00
R13: 0000000180240020 R14: ffff88081ec98150 R15: ffff88075a4a2ee0
FS:  00007f278bae1880(0000) GS:ffff88081ec80000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f841c8ae000 CR3: 000000075bd9c000 CR4: 00000000001407e0
Stack:
 ffff88077bb89600 ffff8807c94a3bf8 ffffffff81206f53 ffff8807c94a3c10
 ffff88077bb89240 0000000000000025 ffff8807c94a3e50 ffff8807c94a3c48
 ffffffff812071ec ffff88077bb89240 ffff88077bb89d40 ffff8807e9403800
Call Trace:
 [<ffffffff81206f53>] shrink_dentry_list+0x113/0x120
 [<ffffffff812071ec>] check_submounts_and_drop+0x7c/0xb0
 [<ffffffff8126a45d>] kernfs_dop_revalidate+0x5d/0xd0
 [<ffffffff811f9a76>] lookup_fast+0x276/0x2f0
 [<ffffffff812efe5c>] ? security_inode_permission+0x1c/0x30
 [<ffffffff811fabc7>] link_path_walk+0x1d7/0xec0
 [<ffffffff8120f784>] ? mntput+0x24/0x40
 [<ffffffff811fb9be>] ? path_lookupat+0x10e/0xd70
 [<ffffffff811fa286>] ? getname_flags+0x56/0x1b0
 [<ffffffff811fb917>] path_lookupat+0x67/0xd70
 [<ffffffff811fa202>] ? final_putname+0x22/0x50
 [<ffffffff81200aa2>] ? user_path_at_empty+0x72/0xd0
 [<ffffffff811d1e85>] ? kmem_cache_alloc+0x35/0x1f0
 [<ffffffff811fa286>] ? getname_flags+0x56/0x1b0
 [<ffffffff811fc64a>] filename_lookup+0x2a/0xd0
 [<ffffffff81200a97>] user_path_at_empty+0x67/0xd0
 [<ffffffff811f447b>] SyS_readlink+0x5b/0x130
 [<ffffffff81710ea9>] system_call_fastpath+0x16/0x1b
Code: 48 8d 7b 80 4c 89 e6 e8 64 fe ff ff 66 83 43 d8 01 31 c9 5b 89 c8 41 5c 5d c3 66 0f 1f 44 00 00 0f 1f 44 00 00 55 48 89 e5 41 54 <53> f7 07 00 04 08 00 48 89 fb 49 89 f4 75 2e 49 8b 14 24 48 8d