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Message-ID: <YFBnypYemiR08A/c@T590>
Date: Tue, 16 Mar 2021 16:09:46 +0800
From: Ming Lei <ming.lei@...hat.com>
To: Sergei Shtepa <sergei.shtepa@...am.com>
Cc: Christoph Hellwig <hch@...radead.org>,
Mike Snitzer <snitzer@...hat.com>,
Alasdair Kergon <agk@...hat.com>,
Hannes Reinecke <hare@...e.de>, Jens Axboe <axboe@...nel.dk>,
dm-devel@...hat.com, linux-block@...r.kernel.org,
linux-kernel@...r.kernel.org, linux-api@...r.kernel.org,
pavel.tide@...am.com
Subject: Re: [PATCH v7 2/3] block: add bdev_interposer
On Fri, Mar 12, 2021 at 06:44:54PM +0300, Sergei Shtepa wrote:
> bdev_interposer allows to redirect bio requests to another devices.
>
> Signed-off-by: Sergei Shtepa <sergei.shtepa@...am.com>
> ---
> block/bio.c | 2 ++
> block/blk-core.c | 57 +++++++++++++++++++++++++++++++++++++++
> block/genhd.c | 54 +++++++++++++++++++++++++++++++++++++
> include/linux/blk_types.h | 3 +++
> include/linux/blkdev.h | 9 +++++++
> 5 files changed, 125 insertions(+)
>
> diff --git a/block/bio.c b/block/bio.c
> index a1c4d2900c7a..0bfbf06475ee 100644
> --- a/block/bio.c
> +++ b/block/bio.c
> @@ -640,6 +640,8 @@ void __bio_clone_fast(struct bio *bio, struct bio *bio_src)
> bio_set_flag(bio, BIO_THROTTLED);
> if (bio_flagged(bio_src, BIO_REMAPPED))
> bio_set_flag(bio, BIO_REMAPPED);
> + if (bio_flagged(bio_src, BIO_INTERPOSED))
> + bio_set_flag(bio, BIO_INTERPOSED);
> bio->bi_opf = bio_src->bi_opf;
> bio->bi_ioprio = bio_src->bi_ioprio;
> bio->bi_write_hint = bio_src->bi_write_hint;
> diff --git a/block/blk-core.c b/block/blk-core.c
> index fc60ff208497..da1abc4c27a9 100644
> --- a/block/blk-core.c
> +++ b/block/blk-core.c
> @@ -1018,6 +1018,55 @@ static blk_qc_t __submit_bio_noacct_mq(struct bio *bio)
> return ret;
> }
>
> +static noinline blk_qc_t submit_bio_interposed(struct bio *bio)
> +{
> + blk_qc_t ret = BLK_QC_T_NONE;
> + struct bio_list bio_list[2] = { };
> + struct gendisk *orig_disk;
> +
> + if (current->bio_list) {
> + bio_list_add(¤t->bio_list[0], bio);
> + return BLK_QC_T_NONE;
> + }
> +
> + orig_disk = bio->bi_bdev->bd_disk;
> + if (unlikely(bio_queue_enter(bio)))
> + return BLK_QC_T_NONE;
> +
> + current->bio_list = bio_list;
> +
> + do {
> + struct block_device *interposer = bio->bi_bdev->bd_interposer;
> +
> + if (unlikely(!interposer)) {
> + /* interposer was removed */
> + bio_list_add(¤t->bio_list[0], bio);
> + break;
> + }
> + /* assign bio to interposer device */
> + bio_set_dev(bio, interposer);
> + bio_set_flag(bio, BIO_INTERPOSED);
> +
> + if (!submit_bio_checks(bio))
> + break;
> + /*
> + * Because the current->bio_list is initialized,
> + * the submit_bio callback will always return BLK_QC_T_NONE.
> + */
> + interposer->bd_disk->fops->submit_bio(bio);
Given original request queue may become live when calling attach() and
detach(), see below comment. bdev_interposer_detach() may be run
when running ->submit_bio(), meantime the interposer device is
gone during the period, then kernel oops.
> + } while (false);
> +
> + current->bio_list = NULL;
> +
> + blk_queue_exit(orig_disk->queue);
> +
> + /* Resubmit remaining bios */
> + while ((bio = bio_list_pop(&bio_list[0])))
> + ret = submit_bio_noacct(bio);
> +
> + return ret;
> +}
> +
> /**
> * submit_bio_noacct - re-submit a bio to the block device layer for I/O
> * @bio: The bio describing the location in memory and on the device.
> @@ -1029,6 +1078,14 @@ static blk_qc_t __submit_bio_noacct_mq(struct bio *bio)
> */
> blk_qc_t submit_bio_noacct(struct bio *bio)
> {
> + /*
> + * Checking the BIO_INTERPOSED flag is necessary so that the bio
> + * created by the bdev_interposer do not get to it for processing.
> + */
> + if (bdev_has_interposer(bio->bi_bdev) &&
> + !bio_flagged(bio, BIO_INTERPOSED))
> + return submit_bio_interposed(bio);
> +
> if (!submit_bio_checks(bio))
> return BLK_QC_T_NONE;
>
> diff --git a/block/genhd.c b/block/genhd.c
> index c55e8f0fced1..c840ecffea68 100644
> --- a/block/genhd.c
> +++ b/block/genhd.c
> @@ -30,6 +30,11 @@
> static struct kobject *block_depr;
>
> DECLARE_RWSEM(bdev_lookup_sem);
> +/*
> + * Prevents different block-layer interposers from attaching or detaching
> + * to the block device at the same time.
> + */
> +static DEFINE_MUTEX(bdev_interposer_attach_lock);
>
> /* for extended dynamic devt allocation, currently only one major is used */
> #define NR_EXT_DEVT (1 << MINORBITS)
> @@ -1940,3 +1945,52 @@ static void disk_release_events(struct gendisk *disk)
> WARN_ON_ONCE(disk->ev && disk->ev->block != 1);
> kfree(disk->ev);
> }
> +
> +int bdev_interposer_attach(struct block_device *original,
> + struct block_device *interposer)
> +{
> + int ret = 0;
> +
> + if (WARN_ON(((!original) || (!interposer))))
> + return -EINVAL;
> + /*
> + * interposer should be simple, no a multi-queue device
> + */
> + if (!interposer->bd_disk->fops->submit_bio)
> + return -EINVAL;
> +
> + if (WARN_ON(!blk_mq_is_queue_frozen(original->bd_disk->queue)))
> + return -EPERM;
The original request queue may become live now...
> +
> + mutex_lock(&bdev_interposer_attach_lock);
> +
> + if (bdev_has_interposer(original))
> + ret = -EBUSY;
> + else {
> + original->bd_interposer = bdgrab(interposer);
> + if (!original->bd_interposer)
> + ret = -ENODEV;
> + }
> +
> + mutex_unlock(&bdev_interposer_attach_lock);
> +
> + return ret;
> +}
> +EXPORT_SYMBOL_GPL(bdev_interposer_attach);
> +
> +void bdev_interposer_detach(struct block_device *original)
> +{
> + if (WARN_ON(!original))
> + return;
> +
> + if (WARN_ON(!blk_mq_is_queue_frozen(original->bd_disk->queue)))
> + return;
The original request queue may become live now...
--
Ming
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