Re: [PATCH] block: return EBUSY from drop_partitions on mounted whole disk device

[Eric Sandeen <sandeen@redhat.com>]

On 8/5/15 2:13 PM, Eric Sandeen wrote:
> The BLKRRPART ioctl already fails today if any partition under
> the device is mounted.  However, if we mkfs a whole disk and mount
> it, BLKRRPART happily proceeds down the invalidation path, which
> seems like a bad idea.
> 
> Check whether the whole device is mounted by checking bd_super,
> and return -EBUSY if so.
> 
> Signed-off-by: Eric Sandeen <sandeen@redhat.com>
> ---
> 
> I don't know for sure if this is the right approach, but figure
> I'll ask in the form of a patch.  ;)

I'm now thinking that this is not the right approach.  :(  I got a
bug report stating that during some md raid1 testing with replacing
failed disks, filesystems were losing data.  I haven't reproduced
that part yet, but...

It's hitting the "bd_super" case added in the patch below, and returning
-EBUSY to md when mdadm tries to to remove a disk:

# mdadm /dev/md0 -r /dev/loop0
mdadm: hot remove failed for /dev/loop0: Device or resource busy

[ 1309.894718] md: cannot remove active disk loop0 from md0 ...
[ 1309.906270] drop_partitions: bd_part_count 0 bd_super ffff880111364000
[ 1309.919295] drop_partitions: s_id md0 uuid 6bb155fe-3ea1-4a84-b66a-d44d44829c36
[ 1309.933878] CPU: 2 PID: 531 Comm: systemd-udevd Not tainted 3.10.0+ #4

I had not thought about "bd_super" existing in this case; I just had my
filesystem hat on.  I'm still digging through the somewhat messy bug
report, I don't know how he's getting to data loss, but that patch
might be half-baked if nothing else because of this behavior...

Note that there are no partitions on md0...

This patch should probably be reverted for now, unless there is some obvious
better fix.

-Eric


> diff --git a/block/partition-generic.c b/block/partition-generic.c
> index 0d9e5f9..04f304c 100644
> --- a/block/partition-generic.c
> +++ b/block/partition-generic.c
> @@ -397,7 +397,7 @@ static int drop_partitions(struct gendisk *disk, struct block_device *bdev)
>  	struct hd_struct *part;
>  	int res;
>  
> -	if (bdev->bd_part_count)
> +	if (bdev->bd_super || bdev->bd_part_count)
>  		return -EBUSY;
>  	res = invalidate_partition(disk, 0);
>  	if (res)
>