On 4/11/22 10:04, Ming Lei wrote: > On Mon, Apr 11, 2022 at 09:50:57AM +0900, Damien Le Moal wrote: >> On 4/11/22 09:36, Ming Lei wrote: >>> On Mon, Apr 11, 2022 at 09:18:56AM +0900, Damien Le Moal wrote: >>>> On 4/9/22 02:12, Ming Lei wrote: >>>>> dm_zone_map_bio() is only called from __map_bio in which the io's >>>>> reference is grabbed already, and the reference won't be released >>>>> until the bio is submitted, so no necessary to do it dm_zone_map_bio >>>>> any more. >>>> >>>> I do not think that this patch is correct. Removing the extra reference on >>>> the io can lead to problems if the io is completed in the target >>>> ->map(ti, clone) call or before dm_zone_map_bio_end() is called for the >>>> DM_MAPIO_SUBMITTED or DM_MAPIO_REMAPPED cases. dm_zone_map_bio_end() needs >>> >>> __map_bio(): >>> ... >>> dm_io_inc_pending(io); >>> ... >>> dm_zone_map_bio(tio); >>> ... >> >> dm-crypt (for instance) may terminate the clone bio immediately in its >> ->map() function context, resulting in the bio_endio()clone) -> >> clone_endio() -> dm_io_dec_pending() call chain. >> >> With that, the io is gone and dm_zone_map_bio_end() will not have a valid >> reference on the orig bio. > > Any target can complete io during ->map. Here looks nothing is special with > dm-crypt or dm-zone, why does only dm zone need extra reference? > > The reference counter is initialized as 1 in init_clone_info(), dm_io_inc_pending() > in __map_bio() increases it to 2, so after the above call chain you mentioned is done, > the counter becomes 1. The original bio can't be completed until dm_io_dec_pending() > in dm_split_and_process_bio() is called. > > Or maybe I miss any extra requirement from dm-zone? I added that extra reference as I discovered it was needed when testing zone append emulation with dm-crypt, back when it was implemented (the emulation, not dm-crypt :)). Let me revisit this. > > > thanks, > Ming > -- > dm-devel mailing list > dm-devel@xxxxxxxxxx > https://listman.redhat.com/mailman/listinfo/dm-devel > -- Damien Le Moal Western Digital Research -- dm-devel mailing list dm-devel@xxxxxxxxxx https://listman.redhat.com/mailman/listinfo/dm-devel
