block: simplify bdev_del_partition()

BLKPG_DEL_PARTITION refuses to delete partitions that still have
openers, i.e., that has an elevated @bdev->bd_openers count. If a device
is claimed by setting @bdev->bd_holder and @bdev->bd_holder_ops
@bdev->bd_openers and @bdev->bd_holders are incremented.
@bdev->bd_openers is effectively guaranteed to be >= @bdev->bd_holders.
So as long as @bdev->bd_openers isn't zero we know that this partition
is still in active use and that there might still be @bdev->bd_holder
and @bdev->bd_holder_ops set.

The only current example is @fs_holder_ops for filesystems. But that
means bdev_mark_dead() which calls into
bdev->bd_holder_ops->mark_dead::fs_bdev_mark_dead() is a nop. As long as
there's an elevated @bdev->bd_openers count we can't delete the
partition and if there isn't an elevated @bdev->bd_openers count then
there's no @bdev->bd_holder or @bdev->bd_holder_ops.

So simply open-code what we need to do. This gets rid of one more
instance where we acquire s_umount under @disk->open_mutex.

Link: https://lore.kernel.org/r/20231016-fototermin-umriss-59f1ea6c1fe6@brauner
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Jan Kara <jack@suse.cz>
Reviewed-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20231017184823.1383356-2-hch@lst.de
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>

diff --git a/block/partitions/core.c b/block/partitions/core.c
index e137a87f4db0d30b6b5e3ab175ba76dc855b5ec1..b0585536b407a576d70bfe4ec4fcff72515a9ef9 100644 (file)
--- a/block/partitions/core.c
+++ b/block/partitions/core.c
@@ -485,7 +485,18 @@ int bdev_del_partition(struct gendisk *disk, int partno)
        if (atomic_read(&part->bd_openers))
                goto out_unlock;
 
-       delete_partition(part);
+       /*
+        * We verified that @part->bd_openers is zero above and so
+        * @part->bd_holder{_ops} can't be set. And since we hold
+        * @disk->open_mutex the device can't be claimed by anyone.
+        *
+        * So no need to call @part->bd_holder_ops->mark_dead() here.
+        * Just delete the partition and invalidate it.
+        */
+
+       remove_inode_hash(part->bd_inode);
+       invalidate_bdev(part);
+       drop_partition(part);
        ret = 0;
 out_unlock:
        mutex_unlock(&disk->open_mutex);