Re: [PATCH 1/2] md: fix WARN_ON if create symlink fail in bind_rdev_to_array()

[Yu Kuai]

Hi,

在 2023/12/25 9:11, Song Liu 写道:
> On Thu, Dec 21, 2023 at 5:17 PM Li Nan <linan666@xxxxxxxxxxxxxxx> wrote:
> > 在 2023/12/22 2:58, Song Liu 写道:
> [...]
> > > In general, I would like to avoid adding flags if possible.
> >
> > This flag is mainly used to fix deadlock in next patch. Or should we
> > export bd_find_holder_disk()? Link hodler if it return NULL.
> > just like:
> >
> >     rdev_for_each_rcu
> >       if (!bd_find_holder_disk)
> >         bd_link_disk_holder
>
> I was thinking we will not need the flag if we fail bind_rdev_to_array()
> on error (below).
>
> > > >    };
> > > >
> > > >    static inline int is_badblock(struct md_rdev *rdev, sector_t s, int sectors,
> > > > diff --git a/drivers/md/md.c b/drivers/md/md.c
> > > > index e05858653a41..d6612b922c76 100644
> > > > --- a/drivers/md/md.c
> > > > +++ b/drivers/md/md.c
> > > > @@ -2526,7 +2526,8 @@ static int bind_rdev_to_array(struct md_rdev *rdev, struct mddev *mddev)
> > > >                   sysfs_get_dirent_safe(rdev->kobj.sd, "bad_blocks");
> > > >
> > > >           list_add_rcu(&rdev->same_set, &mddev->disks);
> > > > -       bd_link_disk_holder(rdev->bdev, mddev->gendisk);
> > > > +       if (!bd_link_disk_holder(rdev->bdev, mddev->gendisk))
> > > > +               set_bit(SymlinkCreated, &rdev->flags);
> > >
> > > Shall we just fail bind_rdev_to_array() if bd_link_disk_holder()
> > > returns non-zero?
> >
> > I keep this action because of commit 00bcb4ac7ee7 ("md: reduce
> > dependence on sysfs."). Fail bind_rdev_to_array is good to me.
>
> I wonder whether the assumption in 00bcb4ac7ee7 is still true. If
> bd_link_disk_holder() fails for valid reasons, we need to handle it
> properly (set a flag, check the flag on unlink, etc.). If we only fail
> bd_link_disk_holder() on extreme cases (ENOMEM, etc.), we can
> just fail bind_rdev_to_array().

I totally agree! Currently, bd_link_disk_holder() from md won't return
-EINVAL, it will return -ENOMEM or -ENODEV if underlying disk is
deleted, which means bind_rdev_to_array() should fail as well.

The only problem is that this will make next patch more complicated, but
I think this can be solved.

Thanks,
Kuai
> Thanks,
> Song
> .