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. > > PS: With an USB3 Lexar (USB Version: 3.00) I get more severe an issue > (not bisected) where I find no way out of reboot. My report to bugzilla > has logs when I was swapping between the these keys. The logs attached > there mixes what looks like two different behaviors. Hi Paolo, >From both Alban's trace and my trace, looks this issue is in BFQ, since request can't be retrieved via e->type->ops.mq.dispatch_request() in blk_mq_do_dispatch_sched() after it is inserted into BFQ's queue. https://bugzilla.kernel.org/show_bug.cgi?id=198023#c4 https://marc.info/?l=linux-block&m=151214241518562&w=2 BTW, I have tried to reproduce the issue with scsi_debug, but not succeed, and it can't be reproduced with other schedulers(mq-deadline, none) too. So could you take a look? Thanks, Ming
