On Mon 16-10-23 17:27:18, Christian Brauner wrote:
> BLKPG_DEL_PARTITION refuses to delete partitions that still have
> openers, i.e., that has an elevated @bdev->bd_openers count. If a device
> is claimed by setting @bdev->bd_holder and @bdev->bd_holder_ops
> @bdev->bd_openers and @bdev->bd_holders are incremented.
> @bdev->bd_openers is effectively guaranteed to be >= @bdev->bd_holders.
> So as long as @bdev->bd_openers isn't zero we know that this partition
> is still in active use and that there might still be @bdev->bd_holder
> and @bdev->bd_holder_ops set.
>
> The only current example is @fs_holder_ops for filesystems. But that
> means bdev_mark_dead() which calls into
> bdev->bd_holder_ops->mark_dead::fs_bdev_mark_dead() is a nop. As long as
> there's an elevated @bdev->bd_openers count we can't delete the
> partition and if there isn't an elevated @bdev->bd_openers count then
> there's no @bdev->bd_holder or @bdev->bd_holder_ops.
>
> So simply open-code what we need to do. This gets rid of one more
> instance where we acquire s_umount under @disk->open_mutex.
>
> Signed-off-by: Christian Brauner <brauner@xxxxxxxxxx>
Looks good to me. Feel free to add:
Reviewed-by: Jan Kara <jack@xxxxxxx>
BTW, now when there's only one delete_partition() caller, we could just
opencode it in its callsite...
Honza
> ---
> Hey Jens,
>
> This came out of an ongoing locking design discussion and is related
> to what we currently have in vfs.super. So if everyone still agrees my
> reasoning is right and you don't have big objections I'd take it through
> there.
>
> As usual, thanks to Jan and Christoph for good discussions here.
>
> Thanks!
> Christian
> ---
> block/partitions/core.c | 13 ++++++++++++-
> 1 file changed, 12 insertions(+), 1 deletion(-)
>
> diff --git a/block/partitions/core.c b/block/partitions/core.c
> index e137a87f4db0..b0585536b407 100644
> --- a/block/partitions/core.c
> +++ b/block/partitions/core.c
> @@ -485,7 +485,18 @@ int bdev_del_partition(struct gendisk *disk, int partno)
> if (atomic_read(&part->bd_openers))
> goto out_unlock;
>
> - delete_partition(part);
> + /*
> + * We verified that @part->bd_openers is zero above and so
> + * @part->bd_holder{_ops} can't be set. And since we hold
> + * @disk->open_mutex the device can't be claimed by anyone.
> + *
> + * So no need to call @part->bd_holder_ops->mark_dead() here.
> + * Just delete the partition and invalidate it.
> + */
> +
> + remove_inode_hash(part->bd_inode);
> + invalidate_bdev(part);
> + drop_partition(part);
> ret = 0;
> out_unlock:
> mutex_unlock(&disk->open_mutex);
> --
> 2.34.1
>
--
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR
