[PATCH 13/14] loop: remove lo_refcount and avoid lo_mutex in ->open / ->release
From: Christoph Hellwig <hch@lst.de>
Date: 2022-03-25 06:40:36
Subsystem:
block layer, the rest · Maintainers:
Jens Axboe, Linus Torvalds
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> --- drivers/block/loop.c | 37 +++++++------------------------------ drivers/block/loop.h | 1 - 2 files changed, 7 insertions(+), 31 deletions(-)
diff --git a/drivers/block/loop.c b/drivers/block/loop.c
index bfd21af7aa38b..8ad8cfffdcbdc 100644
--- a/drivers/block/loop.c
+++ b/drivers/block/loop.c@@ -1261,7 +1261,7 @@ 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; mutex_unlock(&lo->lo_mutex); return 0;
@@ -1741,33 +1741,15 @@ 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); /*
@@ -1777,8 +1759,6 @@ static void lo_release(struct gendisk *disk, fmode_t mode) __loop_clr_fd(lo, true); return; } - -out_unlock: mutex_unlock(&lo->lo_mutex); }
@@ -1792,7 +1772,6 @@ 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
@@ -2046,7 +2025,6 @@ 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);
@@ -2136,13 +2114,12 @@ 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);
diff --git a/drivers/block/loop.h b/drivers/block/loop.h
index 082d4b6bfc6a6..449d562738c52 100644
--- a/drivers/block/loop.h
+++ b/drivers/block/loop.h@@ -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;
--
2.30.2