linux-kernel - Re: [PATCH 3/5] mm/vmalloc: Initialize VA's list node after unlink

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Date:   Thu, 9 Jun 2022 21:30:30 +0800
From:   Baoquan He <bhe@...hat.com>
To:     Uladzislau Rezki <urezki@...il.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Linux Memory Management List <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Christoph Hellwig <hch@...radead.org>,
        Matthew Wilcox <willy@...radead.org>,
        Nicholas Piggin <npiggin@...il.com>,
        Oleksiy Avramchenko <oleksiy.avramchenko@...y.com>
Subject: Re: [PATCH 3/5] mm/vmalloc: Initialize VA's list node after unlink

On 06/09/22 at 02:36pm, Uladzislau Rezki wrote:
> >
> > On 06/07/22 at 11:34am, Uladzislau Rezki (Sony) wrote:
> > > A vmap_area can travel between different places. For example
> > > attached/detached to/from different rb-trees. In order to
> > > prevent fancy bugs, initialize a VA's list node after it is
> > > removed from the list, so it pairs with VA's rb_node which
> > > is also initialized.
> > >
> > > There is no functional change as a result of this patch.
> > >
> > > Signed-off-by: Uladzislau Rezki (Sony) <urezki@...il.com>
> > > ---
> > >  mm/vmalloc.c | 2 +-
> > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > >
> > > diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> > > index 745e89eb6ca1..82771e555273 100644
> > > --- a/mm/vmalloc.c
> > > +++ b/mm/vmalloc.c
> > > @@ -978,7 +978,7 @@ __unlink_va(struct vmap_area *va, struct rb_root *root, bool augment)
> > >       else
> > >               rb_erase(&va->rb_node, root);
> > >
> > > -     list_del(&va->list);
> > > +     list_del_init(&va->list);
> >
> > Don't object this change, while list_del poison members, which is also
> > not bad?
> >
> It is not bad for sure. The main aim was to be align with what the
> RB_CLEAR_NODE() does, i.e. initialize VA when it is detached
> and be safe with list manipulation when it is detached. For example
> whether it is empty or not: list_empty(), etc.

Agree. list_del() can't make list_empty() work, and RB_CLEAR_NODE() has
done the clearing already.

Then this change looks reasonable to me, thanks.

Reviewed-by: Baoquan He <bhe@...hat.com>