Re: blk-mq + bfq: udevd hang on usb2 storages

On Fri, Dec 01, 2017 at 06:04:29PM +0100, Alban Browaeys wrote:

I initially reported as https://bugzilla.kernel.org/show_bug.cgi?id=198
023 .

I have now bisected this issue to commit a6a252e6491443c1c1 "blk-mq-
sched: decide how to handle flush rq via RQF_FLUSH_SEQ".

This is with an USB stick Sandisk Cruzer (USB Version:  2.10) I
regressed with.
systemctl restart systemd-udevd restores sanity.

From my investigation, looks the issue is in BFQ:

	https://marc.info/?l=linux-block&m=151214241518562&w=2

Could you apply the attached debug patch, run your test and provide us the log?

Thanks,
Ming