Comment 7 for bug 1662673

This bug is hitting for me on 16.04 LTS running kernel 4.13.0-16. udev is stuck in the following stack:

[<ffffffff906309eb>] blk_mq_freeze_queue_wait+0x4b/0xb0
[<ffffffff90631f4a>] blk_mq_freeze_queue+0x1a/0x20
[<ffffffffc03d676a>] __nvme_revalidate_disk+0x7a/0x3f0 [nvme_core]
[<ffffffffc03d7bc3>] nvme_revalidate_disk+0x53/0x90 [nvme_core]
[<ffffffff9063b72d>] rescan_partitions+0x8d/0x330
[<ffffffff906374f5>] __blkdev_reread_part+0x65/0x70
[<ffffffff90637523>] blkdev_reread_part+0x23/0x40
[<ffffffff90637ef7>] blkdev_ioctl+0x387/0x910
[<ffffffff9049253d>] block_ioctl+0x3d/0x50
[<ffffffff90467521>] do_vfs_ioctl+0xa1/0x5f0
[<ffffffff90467ae9>] SyS_ioctl+0x79/0x90
[<ffffffff90b0edfb>] entry_SYSCALL_64_fastpath+0x1e/0xa9
[<ffffffffffffffff>] 0xffffffffffffffff

And the process info:

4 D root 797 1 0 80 0 - 11661 blk_mq 03:04 ? 00:00:02 /lib/systemd/systemd-udevd

We have a bunch of read-only parted jobs backing up behind the kernel hang (and possibly causing it in the first place):
root 17317 1 0 03:17 ? 00:00:00 /sbin/parted.rw -m -s -- /dev/nvme0n1 unit B print
root 36839 36832 0 05:39 ? 00:00:00 /sbin/parted.rw -m -s -- /dev/nvme0n1 unit B print
root 37181 37143 0 05:50 ? 00:00:00 /sbin/blockdev --getsize64 /dev/nvme0n1
root 37340 37333 0 06:00 ? 00:00:00 /sbin/parted.rw -m -s -- /dev/nvme0n1 unit B print
root 38585 38549 0 08:29 ? 00:00:00 /sbin/blockdev --getsize64 /dev/nvme0n1
root 38742 38735 0 08:39 ? 00:00:00 /sbin/parted.rw -m -s -- /dev/nvme0n1 unit B print
root 40022 39986 0 11:14 ? 00:00:00 /sbin/blockdev --getsize64 /dev/nvme0n1
root 40184 40177 0 11:24 ? 00:00:00 /sbin/parted.rw -m -s -- /dev/nvme0n1 unit B print
root 41456 41419 0 13:59 ? 00:00:00 /sbin/blockdev --getsize64 /dev/nvme0n1
root 41615 41608 0 14:09 ? 00:00:00 /sbin/parted.rw -m -s -- /dev/nvme0n1 unit B print
root 42905 42869 0 16:44 ? 00:00:00 /sbin/blockdev --getsize64 /dev/nvme0n1
root 43062 43054 0 16:54 ? 00:00:00 /sbin/parted.rw -m -s -- /dev/nvme0n1 unit B print

These are NVME drives with a GPT and two partitions. Let me know if you need more info.