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block: refactor blkdev_get
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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@lst.de>
Acked-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Jan Kara <jack@suse.cz>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
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@axboe
Christoph Hellwig authored and axboe committed Dec 1, 2020
1 parent ec5d451 commit 5b56b6e
Showing 1 changed file with 86 additions and 99 deletions.
185 changes: 86 additions & 99 deletions fs/block_dev.c
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Original file line number Diff line number Diff line change
Expand Up @@ -1407,46 +1407,12 @@ 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;
Expand All @@ -1458,15 +1424,8 @@ 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));
Expand All @@ -1486,14 +1445,23 @@ 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;
}
Expand All @@ -1513,58 +1481,17 @@ 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;
}

Expand All @@ -1589,7 +1516,12 @@ 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;
Expand All @@ -1599,13 +1531,67 @@ 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;
}

Expand Down Expand Up @@ -1753,8 +1739,6 @@ 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);
Expand All @@ -1767,6 +1751,8 @@ 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) {
Expand Down Expand Up @@ -1795,7 +1781,7 @@ 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;
}
}
Expand All @@ -1805,11 +1791,12 @@ 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);

Expand Down

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