Date:   Thu, 16 Feb 2023 14:17:25 +0100
From:   Jan Kara <jack@suse.cz>
To:     Yu Kuai <yukuai1@huaweicloud.com>
Cc:     hch@infradead.org, jack@suse.cz, axboe@kernel.dk,
        linux-block@vger.kernel.org, linux-kernel@vger.kernel.org,
        yukuai3@huawei.com, yi.zhang@huawei.com, yangerkun@huawei.com
Subject: Re: [PATCH -next RFC 2/3] block: factor out the setting of
 GD_NEED_PART_SCAN
Message-ID: <20230216131725.oddv27a7fhz6hx7x@quack3>
References: <20230212092641.2394146-1-yukuai1@huaweicloud.com>
 <20230212092641.2394146-3-yukuai1@huaweicloud.com>
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On Sun 12-02-23 17:26:40, Yu Kuai wrote:
> From: Yu Kuai <yukuai3@huawei.com>
> 
> In order to prevent scan partition for a device that is opened
> exclusively by someone else, new conditions will be added to
> disk_scan_partitions() in the next patch. Hence if device is opened
> exclusively between bdev_add() and disk_scan_partitions(), the first
> partition scan will fail unexpected. This patch factor out the setting
> of GD_NEED_PART_SCAN to prevent the problem.
> 
> Signed-off-by: Yu Kuai <yukuai3@huawei.com>

I'd rather leave the setting of GD_NEED_PART_SCAN in disk_scan_partitions()
to keep it self-contained. On top of that we can set GD_NEED_PART_SCAN in
device_add_disk() to ensure initial partition scan but we should probably
also make sure flags like GD_SUPPRESS_PART_SCAN or GENHD_FL_NO_PART are not
set to avoid unwanted partition scanning.

								Honza

> ---
>  block/genhd.c | 2 +-
>  block/ioctl.c | 1 +
>  2 files changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/block/genhd.c b/block/genhd.c
> index 075d8da284f5..c0d1220bd798 100644
> --- a/block/genhd.c
> +++ b/block/genhd.c
> @@ -367,7 +367,6 @@ int disk_scan_partitions(struct gendisk *disk, fmode_t mode)
>  	if (disk->open_partitions)
>  		return -EBUSY;
>  
> -	set_bit(GD_NEED_PART_SCAN, &disk->state);
>  	bdev = blkdev_get_by_dev(disk_devt(disk), mode, NULL);
>  	if (IS_ERR(bdev))
>  		return PTR_ERR(bdev);
> @@ -493,6 +492,7 @@ int __must_check device_add_disk(struct device *parent, struct gendisk *disk,
>  		if (ret)
>  			goto out_unregister_bdi;
>  
> +		set_bit(GD_NEED_PART_SCAN, &disk->state);
>  		bdev_add(disk->part0, ddev->devt);
>  		if (get_capacity(disk))
>  			disk_scan_partitions(disk, FMODE_READ);
> diff --git a/block/ioctl.c b/block/ioctl.c
> index 6dd49d877584..0eefcdb936a0 100644
> --- a/block/ioctl.c
> +++ b/block/ioctl.c
> @@ -528,6 +528,7 @@ static int blkdev_common_ioctl(struct block_device *bdev, fmode_t mode,
>  			return -EACCES;
>  		if (bdev_is_partition(bdev))
>  			return -EINVAL;
> +		set_bit(GD_NEED_PART_SCAN, &bdev->bd_disk->state);
>  		return disk_scan_partitions(bdev->bd_disk, mode & ~FMODE_EXCL);
>  	case BLKTRACESTART:
>  	case BLKTRACESTOP:
> -- 
> 2.31.1
> 
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR