> Il giorno 07 feb 2018, alle ore 11:15, Mike Galbraith <efault@xxxxxx> ha scritto: > > On Wed, 2018-02-07 at 10:45 +0100, Paolo Valente wrote: >> >>> Il giorno 07 feb 2018, alle ore 10:23, Mike Galbraith <efault@xxxxxx> ha scritto: >>> >>> On Wed, 2018-02-07 at 10:08 +0100, Paolo Valente wrote: >>>> >>>> The first piece of information I need is whether this failure happens >>>> even without "BFQ hierarchical scheduling support". >>> >>> I presume you mean BFQ_GROUP_IOSCHED, which I do not have enabled. >>> >> >> Great (so to speak), this saves us one step. >> >> So, here's my next request for help: please apply the attached patch >> (compressed to preserve it from my email client) and retry. It adds >> several anomaly checks. I hope I have not added any false-positive >> check. > > kernel BUG at block/bfq-iosched.c:4742! > > 4742 BUG_ON(!(rq->rq_flags & RQF_ELVPRIV)); Oh my, this is as crazy as, fortunately, easy to fix. The problem is that this is easy to fix in bfq, but increases the doubts I have expressed in my cover letter: is it ok that, in blk-mq, the functions of an elevator may get invoked, without control, on requests that do not belong to that elevator? Anyway, two requests, Mike, if you haven't had enough already: 1. Could you paste a stack trace for this OOPS, just to understand how we get there? 2. Could you please turn that BUG_ON into: if (!(rq->rq_flags & RQF_ELVPRIV)) return; and see what happens? Thanks a lot, Paolo
