On Mon, May 18 2015 at 11:36am -0400, Jan Kara <jack@xxxxxxx> wrote: > No, I'm not referring to your proposed interface. I'm referring to > current kernel + your patch to remove bio_inc_remaining() from all the dm > targets. Ah, after checking again I see where misunderstanding may have > come from - the device below has to be handled by drivers/md/linear.c which > is MD linear driver, not DM one. I confused those two. Anyway here is the > failure I envision (and frankly, I don't understand dm details much so I may > be just completely wrong but I'd like to understand what prevents the following > from happening): > * We have dm-thin stacked on top of drivers/dm/linear.c > * FS issues bio to dm-thin. remap_and_issue_overwrite() sets bi_end_io to > overwrite_endio. dm-thin eventually calls generic_make_request(bio). > * Now linear_make_request() gets called and it ends up calling > bio_chain(split, bio). This sets BIO_CHAIN on bio. > * IO for all chained bios is completed. So bio->bi_remaining is now zero, > bio still has BIO_CHAIN set and overwrite_endio gets called. > * process_prepared_mapping() will eventually try to call original bi_end_io > callback but that never happens because bi_remaining is 0 and BIO_CHAIN > remained set. Makes sense, you have a valid concern (I knew you and hch must, I just didn't understand). I'll clear the BIO_CHAIN like you suggest and post v2. Thanks! -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
