linux-kernel - Re: [PATCH] block: don't set GD_NEED_PART

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Date:   Wed, 22 Mar 2023 10:52:53 +0100
From:   Jan Kara <jack@...e.cz>
To:     Yu Kuai <yukuai1@...weicloud.com>
Cc:     ming.lei@...hat.com, jack@...e.cz, hch@...radead.org,
        axboe@...nel.dk, yukuai3@...wei.com, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org, yi.zhang@...wei.com,
        yangerkun@...wei.com
Subject: Re: [PATCH] block: don't set GD_NEED_PART_SCAN if scan partition
 failed

On Wed 22-03-23 11:59:26, Yu Kuai wrote:
> From: Yu Kuai <yukuai3@...wei.com>
> 
> Currently if disk_scan_partitions() failed, GD_NEED_PART_SCAN will still
> set, and partition scan will be proceed again when blkdev_get_by_dev()
> is called. However, this will cause a problem that re-assemble partitioned
> raid device will creat partition for underlying disk.
> 
> Test procedure:
> 
> mdadm -CR /dev/md0 -l 1 -n 2 /dev/sda /dev/sdb -e 1.0
> sgdisk -n 0:0:+100MiB /dev/md0
> blockdev --rereadpt /dev/sda
> blockdev --rereadpt /dev/sdb
> mdadm -S /dev/md0
> mdadm -A /dev/md0 /dev/sda /dev/sdb
> 
> Test result: underlying disk partition and raid partition can be
> observed at the same time
> 
> Note that this can still happen in come corner cases that
> GD_NEED_PART_SCAN can be set for underlying disk while re-assemble raid
> device.
> 
> Fixes: e5cfefa97bcc ("block: fix scan partition for exclusively open device again")
> Signed-off-by: Yu Kuai <yukuai3@...wei.com>

This looks good to me. I've actually noticed this problem already when
looking at the patch resulting in commit e5cfefa97bcc but Jens merged it
before I got to checking it and then I've convinced myself it's not serious
enough to redo the patch. Anyway, feel free to add:

Reviewed-by: Jan Kara <jack@...e.cz>

								Honza 

> ---
>  block/genhd.c | 8 +++++++-
>  1 file changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/block/genhd.c b/block/genhd.c
> index 08bb1a9ec22c..a72e27d6779d 100644
> --- a/block/genhd.c
> +++ b/block/genhd.c
> @@ -368,7 +368,6 @@ int disk_scan_partitions(struct gendisk *disk, fmode_t mode)
>  	if (disk->open_partitions)
>  		return -EBUSY;
>  
> -	set_bit(GD_NEED_PART_SCAN, &disk->state);
>  	/*
>  	 * If the device is opened exclusively by current thread already, it's
>  	 * safe to scan partitons, otherwise, use bd_prepare_to_claim() to
> @@ -381,12 +380,19 @@ int disk_scan_partitions(struct gendisk *disk, fmode_t mode)
>  			return ret;
>  	}
>  
> +	set_bit(GD_NEED_PART_SCAN, &disk->state);
>  	bdev = blkdev_get_by_dev(disk_devt(disk), mode & ~FMODE_EXCL, NULL);
>  	if (IS_ERR(bdev))
>  		ret =  PTR_ERR(bdev);
>  	else
>  		blkdev_put(bdev, mode & ~FMODE_EXCL);
>  
> +	/*
> +	 * If blkdev_get_by_dev() failed early, GD_NEED_PART_SCAN is still set,
> +	 * and this will cause that re-assemble partitioned raid device will
> +	 * creat partition for underlying disk.
> +	 */
> +	clear_bit(GD_NEED_PART_SCAN, &disk->state);
>  	if (!(mode & FMODE_EXCL))
>  		bd_abort_claiming(disk->part0, disk_scan_partitions);
>  	return ret;
> -- 
> 2.31.1
> 
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR