当我 cp 或者 dd 一个 ISO (>1GB) 文件到 U 盘时，内核告诉我这个。我 google 了一下，发现这个问题在 Launchpad bug reports 上已经存在好几年了，为什么这么多年了，还是解决不了？我以前用 Fedora，没有这个问题。
操作系统版本：Ubuntu 16.04.3 LTS 内核：4.10.0-28-generic 和 4.10.0-40-generic（均存在相同问题）
Nov 30 23:33:38 UbuntuPC kernel: [ 2417.913106] INFO: task systemd-udevd:295 blocked for more than 120 seconds.
Nov 30 23:33:38 UbuntuPC kernel: [ 2417.913117] Not tainted 4.10.0-28-generic #32~16.04.2-Ubuntu
Nov 30 23:33:38 UbuntuPC kernel: [ 2417.913121] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
Nov 30 23:33:38 UbuntuPC kernel: [ 2417.913127] systemd-udevd D 0 295 1 0x00000004
Nov 30 23:33:38 UbuntuPC kernel: [ 2417.913133] Call Trace:
Nov 30 23:33:38 UbuntuPC kernel: [ 2417.913146] __schedule+0x232/0x700
Nov 30 23:33:38 UbuntuPC kernel: [ 2417.913151] schedule+0x36/0x80
Nov 30 23:33:38 UbuntuPC kernel: [ 2417.913156] schedule_preempt_disabled+0xe/0x10
Nov 30 23:33:38 UbuntuPC kernel: [ 2417.913160] __mutex_lock_slowpath+0x193/0x290
Nov 30 23:33:38 UbuntuPC kernel: [ 2417.913164] mutex_lock+0x2f/0x40
Nov 30 23:33:38 UbuntuPC kernel: [ 2417.913169] __blkdev_get+0x6f/0x400
Nov 30 23:33:38 UbuntuPC kernel: [ 2417.913173] blkdev_get+0x129/0x330
Nov 30 23:33:38 UbuntuPC kernel: [ 2417.913177] blkdev_open+0x82/0xd0
Nov 30 23:33:38 UbuntuPC kernel: [ 2417.913183] do_dentry_open+0x208/0x310
Nov 30 23:33:38 UbuntuPC kernel: [ 2417.913187] ? blkdev_get_by_dev+0x50/0x50
Nov 30 23:33:38 UbuntuPC kernel: [ 2417.913192] vfs_open+0x4c/0x70
Nov 30 23:33:38 UbuntuPC kernel: [ 2417.913196] ? may_open+0x9b/0x100
Nov 30 23:33:38 UbuntuPC kernel: [ 2417.913200] path_openat+0x2ac/0x1430
Nov 30 23:33:38 UbuntuPC kernel: [ 2417.913205] do_filp_open+0x91/0x100
Nov 30 23:33:38 UbuntuPC kernel: [ 2417.913211] ? __alloc_fd+0x46/0x170
Nov 30 23:33:38 UbuntuPC kernel: [ 2417.913216] do_sys_open+0x12d/0x280
Nov 30 23:33:38 UbuntuPC kernel: [ 2417.913222] SyS_open+0x1e/0x20
Nov 30 23:33:38 UbuntuPC kernel: [ 2417.913227] entry_SYSCALL_64_fastpath+0x1e/0xad
Nov 30 23:33:38 UbuntuPC kernel: [ 2417.913231] RIP: 0033:0x7ff789a25c60
Nov 30 23:33:38 UbuntuPC kernel: [ 2417.913234] RSP: 002b:00007fff8a6c70b8 EFLAGS: 00000246 ORIG_RAX: 0000000000000002
Nov 30 23:33:38 UbuntuPC kernel: [ 2417.913239] RAX: ffffffffffffffda RBX: 0000560368fd3cf0 RCX: 00007ff789a25c60
Nov 30 23:33:38 UbuntuPC kernel: [ 2417.913241] RDX: 00005603677f6592 RSI: 00000000000a0800 RDI: 0000560368fd5b90
Nov 30 23:33:38 UbuntuPC kernel: [ 2417.913244] RBP: 0000000000000000 R08: 0000000000000073 R09: 0000000000000003
Nov 30 23:33:38 UbuntuPC kernel: [ 2417.913246] R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
Nov 30 23:33:38 UbuntuPC kernel: [ 2417.913248] R13: 0000560368fd3cf0 R14: 00007fff8a6c7030 R15: 0000000000000000