[PATCH 1/8] block: set the disk capacity to 0 in blk_mark_disk_dead

[Ming Lei]

On Thu, Oct 20, 2022 at 12:56:01PM +0200, Christoph Hellwig wrote:
> nvme and xen-blkfront are already doing this to stop buffered writes from
> creating dirty pages that can't be written out later.  Move it to the
> common code.  Note that this follows the xen-blkfront version that does
> not send and uevent as the uevent is a bit confusing when the device is
> about to go away a little later, and the the size change is just to stop
> buffered writes faster.
> 
> This also removes the comment about the ordering from nvme, as bd_mutex
> not only is gone entirely, but also hasn't been used for locking updates
> to the disk size long before that, and thus the ordering requirement
> documented there doesn't apply any more.
> 
> Signed-off-by: Christoph Hellwig <hch at lst.de>
> ---
>  block/genhd.c                | 3 +++
>  drivers/block/xen-blkfront.c | 1 -
>  drivers/nvme/host/core.c     | 7 +------
>  3 files changed, 4 insertions(+), 7 deletions(-)
> 
> diff --git a/block/genhd.c b/block/genhd.c
> index 17b33c62423df..2877b5f905579 100644
> --- a/block/genhd.c
> +++ b/block/genhd.c
> @@ -555,6 +555,9 @@ void blk_mark_disk_dead(struct gendisk *disk)
>  {
>  	set_bit(GD_DEAD, &disk->state);
>  	blk_queue_start_drain(disk->queue);
> +
> +	/* stop buffered writers from dirtying pages that can't written out */
> +	set_capacity(disk, 0);

The idea makes sense:

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

Just one small issue on mtip32xx, which may call blk_mark_disk_dead() in
irq context, and ->bd_size_lock is actually not irq safe.

But mtip32xx is already broken since blk_queue_start_drain() need mutex,
maybe mtip32xx isn't actively used at all.

Thanks,
Ming