Re: [PATCH 2/5] block: WARN_ON_ONCE() when we remove active partitions

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

On Tue, Oct 17, 2023 at 08:48:20PM +0200, Christoph Hellwig wrote:
> From: Christian Brauner <brauner@kernel.org>
> 
> The logic for disk->open_partitions is:
> 
> blkdev_get_by_*()
> -> bdev_is_partition()
>    -> blkdev_get_part()
>       -> blkdev_get_whole() // bdev_whole->bd_openers++
>       -> if (part->bd_openers == 0)
>                  disk->open_partitions++
>          part->bd_openers
> 
> In other words, when we first claim/open a partition we increment
> disk->open_partitions and only when all part->bd_openers are closed will
> disk->open_partitions be zero. That should mean that
> disk->open_partitions is always > 0 as long as there's anyone that
> has an open partition.
> 
> So the check for disk->open_partitions should meand that we can never
> remove an active partition that has a holder and holder ops set. Assert
> that in the code. The main disk isn't removed so that check doesn't work
> for disk->part0 which is what we want. After all we only care about
> partition not about the main disk.
> 
> Signed-off-by: Christian Brauner <brauner@kernel.org>

inc/dec(part->bd_openers) is always done with ->open_mutex held, so this
change is correct.

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


Thanks,
Ming