On 5/3/19 10:47 AM, Evan Green wrote:
> Hey blockies,
  ^^^^^^^^^^^^

That's the weirdest greeting I have encountered so far on the
linux-block mailing list.

> I'm seeing a hung task in the kernel, and I wanted to share it in case
> it's a known issue. I'm still trying to wrap my head around the stacks
> myself. This is our Chrome OS 4.19 kernel, which is admittedly not
> 100% vanilla mainline master, but we try to keep it pretty close.
> 
> I can reproduce this reliably within our chrome OS installer, where
> it's trying to dd from my system disk (NVMe) to a loop device backed
> by a removable UFS card (4kb sectors) in a USB dongle.

Although this is not the only possible cause such hangs are often caused
by a block driver or SCSI LLD not completing a request. A list of
pending requests can be obtained e.g. by running the attached script.

Bart.