On Mon, May 18 2015 at 11:36am -0400, Jan Kara <[email protected]> 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! -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
