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loop: remove lo_refcount and avoid lo_mutex in ->open / ->release

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lo_refcount counts how many openers a loop device has, but that count
is already provided by the block layer in the bd_openers field of the
whole-disk block_device.  Remove lo_refcount and allow opens to
succeed even on devices beeing deleted - now that ->free_disk is
implemented we can handle that race gracefull and all I/O on it will
just fail. Similarly there is a small race window now where
loop_control_remove does not synchronize the delete vs the remove
due do bd_openers not being under lo_mutex protection, but we can
handle that just as gracefully.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Jan Kara <jack@suse.cz>
Link: https://lore.kernel.org/r/20220330052917.2566582-15-hch@lst.de
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Christoph Hellwig 2022-03-30 07:29:16 +02:00 committed by Jens Axboe
parent 158eaeba4b
commit a0e286b6a5
2 changed files with 7 additions and 31 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

37
drivers/block/loop.c
View File

@ -1244,7 +1244,7 @@ static int loop_clr_fd(struct loop_device *lo)
* <dev>/do something like mkfs/losetup -d <dev> causing the losetup -d
* command to fail with EBUSY.
*/
if (atomic_read(&lo->lo_refcnt) > 1) {
if (disk_openers(lo->lo_disk) > 1) {
lo->lo_flags |= LO_FLAGS_AUTOCLEAR;
loop_global_unlock(lo, true);
return 0;
@ -1725,33 +1725,15 @@ static int lo_compat_ioctl(struct block_device *bdev, fmode_t mode,
}
#endif
static int lo_open(struct block_device *bdev, fmode_t mode)
{
struct loop_device *lo = bdev->bd_disk->private_data;
int err;
err = mutex_lock_killable(&lo->lo_mutex);
if (err)
return err;
if (lo->lo_state == Lo_deleting)
err = -ENXIO;
else
atomic_inc(&lo->lo_refcnt);
mutex_unlock(&lo->lo_mutex);
return err;
}
static void lo_release(struct gendisk *disk, fmode_t mode)
{
struct loop_device *lo = disk->private_data;
mutex_lock(&lo->lo_mutex);
if (atomic_dec_return(&lo->lo_refcnt))
goto out_unlock;
if (disk_openers(disk) > 0)
return;
if (lo->lo_flags & LO_FLAGS_AUTOCLEAR) {
if (lo->lo_state != Lo_bound)
goto out_unlock;
mutex_lock(&lo->lo_mutex);
if (lo->lo_state == Lo_bound && (lo->lo_flags & LO_FLAGS_AUTOCLEAR)) {
lo->lo_state = Lo_rundown;
mutex_unlock(&lo->lo_mutex);
/*
@ -1761,8 +1743,6 @@ static void lo_release(struct gendisk *disk, fmode_t mode)
__loop_clr_fd(lo, true);
return;
}
out_unlock:
mutex_unlock(&lo->lo_mutex);
}
@ -1776,7 +1756,6 @@ static void lo_free_disk(struct gendisk *disk)
static const struct block_device_operations lo_fops = {
.owner = THIS_MODULE,
.open = lo_open,
.release = lo_release,
.ioctl = lo_ioctl,
#ifdef CONFIG_COMPAT
@ -2030,7 +2009,6 @@ static int loop_add(int i)
*/
if (!part_shift)
disk->flags |= GENHD_FL_NO_PART;
atomic_set(&lo->lo_refcnt, 0);
mutex_init(&lo->lo_mutex);
lo->lo_number = i;
spin_lock_init(&lo->lo_lock);
@ -2120,13 +2098,12 @@ static int loop_control_remove(int idx)
ret = mutex_lock_killable(&lo->lo_mutex);
if (ret)
goto mark_visible;
if (lo->lo_state != Lo_unbound ||
atomic_read(&lo->lo_refcnt) > 0) {
if (lo->lo_state != Lo_unbound || disk_openers(lo->lo_disk) > 0) {
mutex_unlock(&lo->lo_mutex);
ret = -EBUSY;
goto mark_visible;
}
/* Mark this loop device no longer open()-able. */
/* Mark this loop device as no more bound, but not quite unbound yet */
lo->lo_state = Lo_deleting;
mutex_unlock(&lo->lo_mutex);

1
drivers/block/loop.h
View File

@ -28,7 +28,6 @@ struct loop_func_table;
struct loop_device {
int lo_number;
atomic_t lo_refcnt;
loff_t lo_offset;
loff_t lo_sizelimit;
int lo_flags;