[dm-devel] [PATCH 20/44] block: refactor blkdev_get
Jan Kara
jack at suse.cz
Thu Nov 26 14:55:21 UTC 2020
On Thu 26-11-20 14:03:58, Christoph Hellwig wrote:
> Move more code that is only run on the outer open but not the open of
> the underlying whole device when opening a partition into blkdev_get,
> which leads to a much easier to follow structure.
>
> This allows to simplify the disk and module refcounting so that one
> reference is held for each open, similar to what we do with normal
> file operations.
>
> Signed-off-by: Christoph Hellwig <hch at lst.de>
> Acked-by: Tejun Heo <tj at kernel.org>
The patch looks good to me. You can add:
Reviewed-by: Jan Kara <jack at suse.cz>
Honza
> ---
> fs/block_dev.c | 185 +++++++++++++++++++++++--------------------------
> 1 file changed, 86 insertions(+), 99 deletions(-)
>
> diff --git a/fs/block_dev.c b/fs/block_dev.c
> index 41c50cfba864e2..86a61a2141f642 100644
> --- a/fs/block_dev.c
> +++ b/fs/block_dev.c
> @@ -1403,46 +1403,12 @@ EXPORT_SYMBOL_GPL(bdev_disk_changed);
> * mutex_lock(part->bd_mutex)
> * mutex_lock_nested(whole->bd_mutex, 1)
> */
> -
> -static int __blkdev_get(struct block_device *bdev, fmode_t mode, void *holder,
> - int for_part)
> +static int __blkdev_get(struct block_device *bdev, struct gendisk *disk,
> + int partno, fmode_t mode)
> {
> - struct block_device *whole = NULL, *claiming = NULL;
> - struct gendisk *disk;
> int ret;
> - int partno;
> - bool first_open = false, unblock_events = true, need_restart;
> -
> - restart:
> - need_restart = false;
> - ret = -ENXIO;
> - disk = bdev_get_gendisk(bdev, &partno);
> - if (!disk)
> - goto out;
> -
> - if (partno) {
> - whole = bdget_disk(disk, 0);
> - if (!whole) {
> - ret = -ENOMEM;
> - goto out_put_disk;
> - }
> - }
>
> - if (!for_part && (mode & FMODE_EXCL)) {
> - WARN_ON_ONCE(!holder);
> - if (whole)
> - claiming = whole;
> - else
> - claiming = bdev;
> - ret = bd_prepare_to_claim(bdev, claiming, holder);
> - if (ret)
> - goto out_put_whole;
> - }
> -
> - disk_block_events(disk);
> - mutex_lock_nested(&bdev->bd_mutex, for_part);
> if (!bdev->bd_openers) {
> - first_open = true;
> bdev->bd_disk = disk;
> bdev->bd_contains = bdev;
> bdev->bd_partno = partno;
> @@ -1454,15 +1420,8 @@ static int __blkdev_get(struct block_device *bdev, fmode_t mode, void *holder,
> goto out_clear;
>
> ret = 0;
> - if (disk->fops->open) {
> + if (disk->fops->open)
> ret = disk->fops->open(bdev, mode);
> - /*
> - * If we lost a race with 'disk' being deleted,
> - * try again. See md.c
> - */
> - if (ret == -ERESTARTSYS)
> - need_restart = true;
> - }
>
> if (!ret) {
> bd_set_nr_sectors(bdev, get_capacity(disk));
> @@ -1482,14 +1441,23 @@ static int __blkdev_get(struct block_device *bdev, fmode_t mode, void *holder,
> if (ret)
> goto out_clear;
> } else {
> - BUG_ON(for_part);
> - ret = __blkdev_get(whole, mode, NULL, 1);
> - if (ret)
> + struct block_device *whole = bdget_disk(disk, 0);
> +
> + mutex_lock_nested(&whole->bd_mutex, 1);
> + ret = __blkdev_get(whole, disk, 0, mode);
> + if (ret) {
> + mutex_unlock(&whole->bd_mutex);
> + bdput(whole);
> goto out_clear;
> - bdev->bd_contains = bdgrab(whole);
> + }
> + whole->bd_part_count++;
> + mutex_unlock(&whole->bd_mutex);
> +
> + bdev->bd_contains = whole;
> bdev->bd_part = disk_get_part(disk, partno);
> if (!(disk->flags & GENHD_FL_UP) ||
> !bdev->bd_part || !bdev->bd_part->nr_sects) {
> + __blkdev_put(whole, mode, 1);
> ret = -ENXIO;
> goto out_clear;
> }
> @@ -1509,58 +1477,17 @@ static int __blkdev_get(struct block_device *bdev, fmode_t mode, void *holder,
> (!ret || ret == -ENOMEDIUM))
> bdev_disk_changed(bdev, ret == -ENOMEDIUM);
> if (ret)
> - goto out_unlock_bdev;
> + return ret;
> }
> }
> bdev->bd_openers++;
> - if (for_part)
> - bdev->bd_part_count++;
> - if (claiming)
> - bd_finish_claiming(bdev, claiming, holder);
> -
> - /*
> - * Block event polling for write claims if requested. Any write holder
> - * makes the write_holder state stick until all are released. This is
> - * good enough and tracking individual writeable reference is too
> - * fragile given the way @mode is used in blkdev_get/put().
> - */
> - if (claiming && (mode & FMODE_WRITE) && !bdev->bd_write_holder &&
> - (disk->flags & GENHD_FL_BLOCK_EVENTS_ON_EXCL_WRITE)) {
> - bdev->bd_write_holder = true;
> - unblock_events = false;
> - }
> - mutex_unlock(&bdev->bd_mutex);
> -
> - if (unblock_events)
> - disk_unblock_events(disk);
> -
> - /* only one opener holds refs to the module and disk */
> - if (!first_open)
> - put_disk_and_module(disk);
> - if (whole)
> - bdput(whole);
> return 0;
>
> out_clear:
> disk_put_part(bdev->bd_part);
> bdev->bd_disk = NULL;
> bdev->bd_part = NULL;
> - if (bdev != bdev->bd_contains)
> - __blkdev_put(bdev->bd_contains, mode, 1);
> bdev->bd_contains = NULL;
> - out_unlock_bdev:
> - if (claiming)
> - bd_abort_claiming(bdev, claiming, holder);
> - mutex_unlock(&bdev->bd_mutex);
> - disk_unblock_events(disk);
> - out_put_whole:
> - if (whole)
> - bdput(whole);
> - out_put_disk:
> - put_disk_and_module(disk);
> - if (need_restart)
> - goto restart;
> - out:
> return ret;
> }
>
> @@ -1585,7 +1512,12 @@ static int __blkdev_get(struct block_device *bdev, fmode_t mode, void *holder,
> */
> static int blkdev_get(struct block_device *bdev, fmode_t mode, void *holder)
> {
> - int ret, perm = 0;
> + struct block_device *claiming;
> + bool unblock_events = true;
> + struct gendisk *disk;
> + int perm = 0;
> + int partno;
> + int ret;
>
> if (mode & FMODE_READ)
> perm |= MAY_READ;
> @@ -1595,13 +1527,67 @@ static int blkdev_get(struct block_device *bdev, fmode_t mode, void *holder)
> if (ret)
> goto bdput;
>
> - ret =__blkdev_get(bdev, mode, holder, 0);
> - if (ret)
> + /*
> + * If we lost a race with 'disk' being deleted, try again. See md.c.
> + */
> +retry:
> + ret = -ENXIO;
> + disk = bdev_get_gendisk(bdev, &partno);
> + if (!disk)
> goto bdput;
> - return 0;
>
> + if (mode & FMODE_EXCL) {
> + WARN_ON_ONCE(!holder);
> +
> + ret = -ENOMEM;
> + claiming = bdget_disk(disk, 0);
> + if (!claiming)
> + goto put_disk;
> + ret = bd_prepare_to_claim(bdev, claiming, holder);
> + if (ret)
> + goto put_claiming;
> + }
> +
> + disk_block_events(disk);
> +
> + mutex_lock(&bdev->bd_mutex);
> + ret =__blkdev_get(bdev, disk, partno, mode);
> + if (!(mode & FMODE_EXCL)) {
> + ; /* nothing to do here */
> + } else if (ret) {
> + bd_abort_claiming(bdev, claiming, holder);
> + } else {
> + bd_finish_claiming(bdev, claiming, holder);
> +
> + /*
> + * Block event polling for write claims if requested. Any write
> + * holder makes the write_holder state stick until all are
> + * released. This is good enough and tracking individual
> + * writeable reference is too fragile given the way @mode is
> + * used in blkdev_get/put().
> + */
> + if ((mode & FMODE_WRITE) && !bdev->bd_write_holder &&
> + (disk->flags & GENHD_FL_BLOCK_EVENTS_ON_EXCL_WRITE)) {
> + bdev->bd_write_holder = true;
> + unblock_events = false;
> + }
> + }
> + mutex_unlock(&bdev->bd_mutex);
> +
> + if (unblock_events)
> + disk_unblock_events(disk);
> +
> +put_claiming:
> + if (mode & FMODE_EXCL)
> + bdput(claiming);
> +put_disk:
> + if (ret)
> + put_disk_and_module(disk);
> + if (ret == -ERESTARTSYS)
> + goto retry;
> bdput:
> - bdput(bdev);
> + if (ret)
> + bdput(bdev);
> return ret;
> }
>
> @@ -1749,8 +1735,6 @@ static void __blkdev_put(struct block_device *bdev, fmode_t mode, int for_part)
> if (bdev_is_partition(bdev))
> victim = bdev->bd_contains;
> bdev->bd_contains = NULL;
> -
> - put_disk_and_module(disk);
> } else {
> if (!bdev_is_partition(bdev) && disk->fops->release)
> disk->fops->release(disk, mode);
> @@ -1763,6 +1747,8 @@ static void __blkdev_put(struct block_device *bdev, fmode_t mode, int for_part)
>
> void blkdev_put(struct block_device *bdev, fmode_t mode)
> {
> + struct gendisk *disk = bdev->bd_disk;
> +
> mutex_lock(&bdev->bd_mutex);
>
> if (mode & FMODE_EXCL) {
> @@ -1791,7 +1777,7 @@ void blkdev_put(struct block_device *bdev, fmode_t mode)
> * unblock evpoll if it was a write holder.
> */
> if (bdev_free && bdev->bd_write_holder) {
> - disk_unblock_events(bdev->bd_disk);
> + disk_unblock_events(disk);
> bdev->bd_write_holder = false;
> }
> }
> @@ -1801,11 +1787,12 @@ void blkdev_put(struct block_device *bdev, fmode_t mode)
> * event. This is to ensure detection of media removal commanded
> * from userland - e.g. eject(1).
> */
> - disk_flush_events(bdev->bd_disk, DISK_EVENT_MEDIA_CHANGE);
> + disk_flush_events(disk, DISK_EVENT_MEDIA_CHANGE);
>
> mutex_unlock(&bdev->bd_mutex);
>
> __blkdev_put(bdev, mode, 0);
> + put_disk_and_module(disk);
> }
> EXPORT_SYMBOL(blkdev_put);
>
> --
> 2.29.2
>
--
Jan Kara <jack at suse.com>
SUSE Labs, CR
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