Hello, under kernel when i am using the mq-bfq i/o scheduler i cannot mount any usb drives and some apps are hanging.This issue is limited only to using mq-bfq scheduler under the 4.15 kernel series,mq-bfq worked fine with 4.14.x and all the other schedulers work properly on 4.15.x.
bisected between 4.14 and 4.15 first bad commit was a6a252e6491443c1c18eab7e254daee63d4a7a04
running blkid the command will hang in the D state on this commit but not its parent if a USB thumb drive is present and the bfq scheduler is used for that device.
Appears to be this issue http://lkml.org/lkml/2018/2/7/529
Resolved in kernel 4.15.3
Reopend only two of my flash drives work with the current state of bfq a data traveller 4.0gb usb2 and a no name 1gb usb2 drive which is weird.
Problem persists with kernel 4.15.8 ,but has been resolved in linux 4.16 mainline since rc1, last time i checked.
Issue resolved under kernel 4.15.10