> If I understand plugging correctly then when a process is going to wait
> on the I/O to finish (here submit_bio_wait(), the device is unplugged
> and request dispatching to the device driver is started. Does that mean
> we should finish plug before we wait ?
Oh, where should I find to unplug during submit_bio_wait() call? I
cannot find it. But, there is no stuck during the call, it's weird to
me. :( Could you explain to me?
2020년 6월 11일 (목) 오전 10:35, Chaitanya Kulkarni <Chaitanya.Kulkarni@xxxxxxx>님이 작성:
>
> Daeho,
>
> On 6/8/20 8:05 PM, Daeho Jeong wrote:
> > Hi guys,
> >
> > When I looked into blkdev_issue_zeroout(), I found something that I
> > cannot understand there. In my understanding, all the submitted bio
> > will stay in the plug list during plugging. But, I found
> > submit_bio_wait() calling during the plugging. I guess the below
> > submit_bio_wait() might wait forever in the lower kernel version like
> > 4.14, because of plugging. If I am wrong, plz, correct me.
> >
> > >>> blk_start_plug(&plug); <<<
> > if (try_write_zeroes) {
> > ret = __blkdev_issue_write_zeroes(bdev, sector, nr_sects,
> > gfp_mask, &bio, flags);
> > } else if (!(flags & BLKDEV_ZERO_NOFALLBACK)) {
> > ret = __blkdev_issue_zero_pages(bdev, sector, nr_sects,
> > gfp_mask, &bio);
> > } else {
> > /* No zeroing offload support */
> > ret = -EOPNOTSUPP;
> > }
> > if (ret == 0 && bio) {
> > ret = submit_bio_wait(bio);
> > bio_put(bio);
> > }
> > >>> blk_finish_plug(&plug); <<<
> >
>
> If your analysis is correct then this is true for
> blkdev_issue_write_same() and blkdev_issue_discard() also ?
>
> If I understand plugging correctly then when a process is going to wait
> on the I/O to finish (here submit_bio_wait(), the device is unplugged
> and request dispatching to the device driver is started. Does that mean
> we should finish plug before we wait ?
>
> Just for a discussion following untested patch which unplugs before
> submit_bio_wait() in blk-lib.c and maintains the original behaviour :-
>
> From 253ae720f721b2789d8fcde3861aeac6766b4836 Mon Sep 17 00:00:00 2001
> From: Chaitanya Kulkarni <chaitanya.kulkarni@xxxxxxx>
> Date: Wed, 10 Jun 2020 18:23:19 -0700
> Subject: [PATCH] block: finish plug before submit_bio_wait()
>
> Signed-off-by: Chaitanya Kulkarni <chaitanya.kulkarni@xxxxxxx>
> ---
> block/blk-lib.c | 6 +++---
> 1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/block/blk-lib.c b/block/blk-lib.c
> index 5f2c429d4378..992de09b258d 100644
> --- a/block/blk-lib.c
> +++ b/block/blk-lib.c
> @@ -104,13 +104,13 @@ int blkdev_issue_discard(struct block_device
> *bdev, sector_t sector,
> blk_start_plug(&plug);
> ret = __blkdev_issue_discard(bdev, sector, nr_sects, gfp_mask, flags,
> &bio);
> + blk_finish_plug(&plug);
> if (!ret && bio) {
> ret = submit_bio_wait(bio);
> if (ret == -EOPNOTSUPP)
> ret = 0;
> bio_put(bio);
> }
> - blk_finish_plug(&plug);
>
> return ret;
> }
> @@ -200,11 +200,11 @@ int blkdev_issue_write_same(struct block_device
> *bdev, sector_t sector,
> blk_start_plug(&plug);
> ret = __blkdev_issue_write_same(bdev, sector, nr_sects, gfp_mask, page,
> &bio);
> + blk_finish_plug(&plug);
> if (ret == 0 && bio) {
> ret = submit_bio_wait(bio);
> bio_put(bio);
> }
> - blk_finish_plug(&plug);
> return ret;
> }
> EXPORT_SYMBOL(blkdev_issue_write_same);
> @@ -381,11 +381,11 @@ int blkdev_issue_zeroout(struct block_device
> *bdev, sector_t sector,
> /* No zeroing offload support */
> ret = -EOPNOTSUPP;
> }
> + blk_finish_plug(&plug);
> if (ret == 0 && bio) {
> ret = submit_bio_wait(bio);
> bio_put(bio);
> }
> - blk_finish_plug(&plug);
> if (ret && try_write_zeroes) {
> if (!(flags & BLKDEV_ZERO_NOFALLBACK)) {
> try_write_zeroes = false;
> --
> 2.27.0
>
