Re: [PATCH 1/5] block: simplify bdev_del_partition()

[Ming Lei <ming.lei@redhat.com>]

On Tue, Oct 17, 2023 at 08:48:19PM +0200, Christoph Hellwig wrote:
> From: Christian Brauner <brauner@kernel.org>
> 
> 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: Christian Brauner <brauner@kernel.org>
> Signed-off-by: Christoph Hellwig <hch@lst.de>

inc/dec(part->bd_openers) is always done with ->open_mutex held, so this
change is correct.

Reviewed-by: Ming Lei <ming.lei@redhat.com>

Thanks,
Ming