On Tue, Jun 22, 2021 at 10:26:15AM +0800, JeffleXu wrote: > > > On 6/21/21 10:04 PM, Ming Lei wrote: > > On Mon, Jun 21, 2021 at 07:33:34PM +0800, JeffleXu wrote: > >> > >> > >> On 6/18/21 10:39 PM, Ming Lei wrote: > >>> From 47e523b9ee988317369eaadb96826323cd86819e Mon Sep 17 00:00:00 2001 > >>> From: Ming Lei <ming.lei@xxxxxxxxxx> > >>> Date: Wed, 16 Jun 2021 16:13:46 +0800 > >>> Subject: [RFC PATCH V3 3/3] dm: support bio polling > >>> > >>> Support bio(REQ_POLLED) polling in the following approach: > >>> > >>> 1) only support io polling on normal READ/WRITE, and other abnormal IOs > >>> still fallback on IRQ mode, so the target io is exactly inside the dm > >>> io. > >>> > >>> 2) hold one refcnt on io->io_count after submitting this dm bio with > >>> REQ_POLLED > >>> > >>> 3) support dm native bio splitting, any dm io instance associated with > >>> current bio will be added into one list which head is bio->bi_end_io > >>> which will be recovered before ending this bio > >>> > >>> 4) implement .poll_bio() callback, call bio_poll() on the single target > >>> bio inside the dm io which is retrieved via bio->bi_bio_drv_data; call > >>> dec_pending() after the target io is done in .poll_bio() > >>> > >>> 4) enable QUEUE_FLAG_POLL if all underlying queues enable QUEUE_FLAG_POLL, > >>> which is based on Jeffle's previous patch. > >>> > >>> Signed-off-by: Ming Lei <ming.lei@xxxxxxxxxx> > >>> --- > >>> V3: > >>> - covers all comments from Jeffle > >>> - fix corner cases when polling on abnormal ios > >>> > >> ... > >> > >> One bug and one performance issue, though I haven't investigated deep > >> for both. > >> > >> > >> kernel base: based on Jens' for-next, applying Christoph and Leiming's > >> patchset. > >> > >> > >> 1. One bug when there's DM device stack, e.g., dm-linear upon another > >> dm-linear. Can be reproduced by following steps: > >> > >> ``` > >> $ sudo dmsetup create tmpdev --table '0 2097152 linear /dev/nvme0n1 0' > >> > >> $ cat tmp.table > >> 0 2097152 linear /dev/mapper/tmpdev 0 > >> 2097152 2097152 linear /dev/nvme0n1 0 > >> > >> $ cat tmp.table | dmsetup create testdev > >> > >> $ fio -name=test -ioengine=io_uring -iodepth=128 -numjobs=1 -thread > >> -rw=randread -direct=1 -bs=4k -time_based -runtime=10 -cpus_allowed=6 > >> -filename=/dev/mapper/testdev -hipri=1 > >> ``` > >> > >> > >> BUG: unable to handle page fault for address: ffffffffc01a6208 > >> #PF: supervisor write access in kernel mode > >> #PF: error_code(0x0003) - permissions violation > >> PGD 39740c067 P4D 39740c067 PUD 39740e067 PMD 1035db067 PTE 1ddf6f061 > >> Oops: 0003 [#1] SMP PTI > >> CPU: 6 PID: 5899 Comm: fio Tainted: G S > >> 5.13.0-0.1.git.81bcdc3.al7.x86_64 #1 > >> Hardware name: Inventec K900G3-10G/B900G3, BIOS A2.20 06/23/2017 > >> RIP: 0010:dm_submit_bio+0x171/0x3e0 [dm_mod] > > > > It has been fixed in my local repo: > > > > @@ -1608,6 +1649,7 @@ static void init_clone_info(struct clone_info *ci, struct mapped_device *md, > > ci->map = map; > > ci->io = alloc_io(md, bio); > > ci->sector = bio->bi_iter.bi_sector; > > + ci->submit_as_polled = false; > > > > It doesn't work in my test environment. Actually the following fix > should be applied. > > > @@ -1390,6 +1403,8 @@ static int clone_bio(struct dm_target_io *tio, > struct bio *bio, > if (bio_integrity(bio)) > bio_integrity_trim(clone); > > + clone->bi_opf &= ~REQ_SAVED_END_IO; > + This change is good, but it shouldn't fix the panic except for nested device map, I will fold into V3. > return 0; > } > > > The rationale is that, REQ_SAVED_END_IO should be cleared once the bio > *passes through* the device stack layer. Or the cloned bio for next > layer will inherit REQ_SAVED_END_IO flag, in which case > 'cloned_bio->bi_end_io' (actually acts as the hlist head) won't be > initialized in dm_setup_polled_io(), and thus it gets crashed when > trying to insert into this hash list in __split_and_process_bio(). 'cloned_bio' can't reach dm_submit_bio() if it isn't one DM bio. Thanks, Ming
