On 6/22/21 10:45 AM, Ming Lei wrote: > 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. The panic I posted exactly happen for nested device map. >> >> 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. > 'cloned_bio' actually refers to dm_io.tio.clone, i.e., the cloned bio used to submit to the device of the next level. dm1 /\ dm2 NVMe1 /\ NVMe2 NVMe3 For the above example, 'cloned_bio' refers to dm_io.tio.clone, where this dm_io is to be submitted to dm2. @bi_private split bio ------------------> original bio (for dm1) ^ ^ | @orig_bio | @orig_bio | | dm_io(for dm2) dm_io(for NVME1) struct dm_target_io tio struct bio clone (...following omitted for NVMe2 and NVMe3) I mean, for above 'struct bio clone', REQ_SAVED_END_IO shall be cleared. -- Thanks, Jeffle -- dm-devel mailing list dm-devel@xxxxxxxxxx https://listman.redhat.com/mailman/listinfo/dm-devel