Re: [PATCH -next 3/7] md: don't rely on 'mddev->pers' to be set in mddev_suspend()

[Yu Kuai]

Hi,

在 2023/08/22 8:13, Song Liu 写道:
> On Thu, Aug 3, 2023 at 6:30 AM Yu Kuai <yukuai1@xxxxxxxxxxxxxxx> wrote:
> > From: Yu Kuai <yukuai3@xxxxxxxxxx>
> >
> > Now that active io is initialized when mddev is allocated, it's safe to
> > call mddev_suspend() before 'mddev->pers' is set.
> >
> > This also prevent null-ptr-def in some cases that caller doesn't
> > guarantee 'mddev->pers' to be set.
>
> This description is a little confusing (to me at least). Please revise it.

Sorry about this, how about this:

'active_io' used to be initialized while the array is running, and
'mddev->pers' is set while the array is running as well. Hence caller
must hold 'reconfig_mutex' and guarantee 'mddev->pers' is set before
calling mddev_suspend().

Now that 'active_io' is initialized when mddev is allocated, such
restriction doesn't exist anymore. In the meantime, follow up patches
will refactor mddev_suspend(), hence add checking for 'mddev->pers' to
prevent null-ptr-deref.

Thanks,
Kuai

> Other than that, the set looks good to me.
>
> Thanks,
> Song
>
> > Signed-off-by: Yu Kuai <yukuai3@xxxxxxxxxx>
> > ---
> >   drivers/md/md.c | 2 +-
> >   1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/md/md.c b/drivers/md/md.c
> > index 897e94a9e47d..f14f2f0a9484 100644
> > --- a/drivers/md/md.c
> > +++ b/drivers/md/md.c
> > @@ -448,7 +448,7 @@ void mddev_suspend(struct mddev *mddev)
> >          set_bit(MD_ALLOW_SB_UPDATE, &mddev->flags);
> >          percpu_ref_kill(&mddev->active_io);
> >
> > -       if (mddev->pers->prepare_suspend)
> > +       if (mddev->pers && mddev->pers->prepare_suspend)
> >                  mddev->pers->prepare_suspend(mddev);
> >
> >          wait_event(mddev->sb_wait, percpu_ref_is_zero(&mddev->active_io));
> > --
> > 2.39.2
> .