Re: [PATCH -next RFC 2/3] block: factor out the setting of GD_NEED_PART_SCAN

[Yu Kuai]

Hi,

在 2023/02/12 19:36, Hannes Reinecke 写道:
> On 2/12/23 10:26, Yu Kuai wrote:
> > From: Yu Kuai <yukuai3@xxxxxxxxxx>
> >
> > 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@xxxxxxxxxx>
> > ---
> >   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);
> Usual caveat:
> What happens if the flag is already set here?
> Wouldn't that imply that another scan is underway?

I think this is not true, currently set the state just means we're going
to scan, and if some checking failed, the state will be left. I don't
have a good idea how to fix this yet...

Thanks,
Kuai

> And wouldn't it be better to use 'test_and_set()'?
>
>
> > 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:
> Similar here.
>
> Cheers,
>
> Hannes