Re: [PATCH 3/9] block: unhash the whole device inode earlier

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

On Thu, Jul 22, 2021 at 09:53:56AM +0200, Christoph Hellwig wrote:
> Unhash the whole device inode early in del_gendisk.  This allows to
> remove the first GENHD_FL_UP check in the open path as we simply
> won't find a just removed inode.  The second non-racy check after
> taking open_mutex is still kept.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
>  block/genhd.c  | 7 +------
>  fs/block_dev.c | 2 +-
>  2 files changed, 2 insertions(+), 7 deletions(-)
> 
> diff --git a/block/genhd.c b/block/genhd.c
> index 298ee78c1bda..716f5ca479ad 100644
> --- a/block/genhd.c
> +++ b/block/genhd.c
> @@ -585,6 +585,7 @@ void del_gendisk(struct gendisk *disk)
>  	disk_del_events(disk);
>  
>  	mutex_lock(&disk->open_mutex);
> +	remove_inode_hash(disk->part0->bd_inode);
>  	disk->flags &= ~GENHD_FL_UP;
>  	blk_drop_partitions(disk);
>  	mutex_unlock(&disk->open_mutex);
> @@ -592,12 +593,6 @@ void del_gendisk(struct gendisk *disk)
>  	fsync_bdev(disk->part0);
>  	__invalidate_device(disk->part0, true);
>  
> -	/*
> -	 * Unhash the bdev inode for this device so that it can't be looked
> -	 * up any more even if openers still hold references to it.
> -	 */
> -	remove_inode_hash(disk->part0->bd_inode);
> -
>  	set_capacity(disk, 0);
>  
>  	if (!(disk->flags & GENHD_FL_HIDDEN)) {
> diff --git a/fs/block_dev.c b/fs/block_dev.c
> index 9ef4f1fc2cb0..932f4034ad66 100644
> --- a/fs/block_dev.c
> +++ b/fs/block_dev.c
> @@ -1340,7 +1340,7 @@ struct block_device *blkdev_get_no_open(dev_t dev)
>  	disk = bdev->bd_disk;
>  	if (!kobject_get_unless_zero(&disk_to_dev(disk)->kobj))
>  		goto bdput;
> -	if ((disk->flags & (GENHD_FL_UP | GENHD_FL_HIDDEN)) != GENHD_FL_UP)
> +	if (disk->flags & GENHD_FL_HIDDEN)

But del_gendisk() can be called just between bdget() and checking GENHD_FL_UP.

And not see difference by moving remove_inode_hash() with disk open_mutex held.


Thanks,
Ming