On 12/7/18 9:19 AM, Bart Van Assche wrote: > On Thu, 2018-12-06 at 22:17 -0700, Jens Axboe wrote: >> Instead of making special cases for what we can direct issue, and now >> having to deal with DM solving the livelock while still retaining a BUSY >> condition feedback loop, always just add a request that has been through >> ->queue_rq() to the hardware queue dispatch list. These are safe to use >> as no merging can take place there. Additionally, if requests do have >> prepped data from drivers, we aren't dependent on them not sharing space >> in the request structure to safely add them to the IO scheduler lists. > > How about making blk_mq_sched_insert_request() complain if a request is passed > to it in which the RQF_DONTPREP flag has been set to avoid that this problem is > reintroduced in the future? Otherwise this patch looks fine to me. I agree, but I think we should do that as a follow up patch. I don't want to touch this one if we can avoid it. The thought did cross my mind, too. It should be impossible now that everything goes to the dispatch list. -- Jens Axboe
