The gendisk of raid can't be released

The gendisk of raid can't be released

[Xiao Ni]

Hi Christoph

There is a regression problem which is introduced by 84d7d462b16d
(blk-cgroup: pin the gendisk in struct blkcg_gq).

The test commands below can reproduce this:
mdadm -CR /dev/md0 -l10 -n4 /dev/nvme[0-3]n1 --assume-clean
mdadm --stop /dev/md0
mdadm -CR /dev/md0 -l10 -n4 /dev/nvme[0-3]n1 --assume-clean
mdadm: Fail to create md0 when using
/sys/module/md_mod/parameters/new_array, fallback to creation via node
mdadm: unexpected failure opening /dev/md0

The reason is that the gendisk kobj can't be released, so md_free_disk
can't be called. It looks like the patch mentioned above doesn't have
problem. Before this patch, it didn't add the reference to the kobj of
the gendisk. So all things work well. Now it adds the reference to
the kobj of the gendisk in blkg_alloc, but it can't be decremented in
blkg_release. After adding some debug logs, it only adds the reference
of blkg->refcnt, but it doesn't call blkcg_rstat_flush which calls
percpu_ref_put.

So the patch 84d7d462b16d only exposes the reference problem in
block cgroup.

Best Regards
Xiao

Re: The gendisk of raid can't be released

[Ming Lei]

On Thu, Mar 02, 2023 at 11:51:59PM +0800, Xiao Ni wrote:
> Hi Christoph
> 
> There is a regression problem which is introduced by 84d7d462b16d
> (blk-cgroup: pin the gendisk in struct blkcg_gq).

The above commit has been reverted, can you test the latest linus tree?


Thanks,
Ming

Re: The gendisk of raid can't be released

[Xiao Ni]

On Fri, Mar 3, 2023 at 10:54 AM Ming Lei <ming.lei@redhat.com> wrote:
>
> On Thu, Mar 02, 2023 at 11:51:59PM +0800, Xiao Ni wrote:
> > Hi Christoph
> >
> > There is a regression problem which is introduced by 84d7d462b16d
> > (blk-cgroup: pin the gendisk in struct blkcg_gq).
>
> The above commit has been reverted, can you test the latest linus tree?
>
>
> Thanks,
> Ming
>

Thanks for the information. I have tried with the latest linux-next version. The
problem doesn't appear anymore.

Best regards
Xiao