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

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Message-ID: <CA+KHdyWDSUgFQnCPr_i=NwoDNFiqP2Q6Z6pik3djK=TQ=hoSZQ@mail.gmail.com>
Date:   Thu, 9 Jun 2022 14:36:22 +0200
From:   Uladzislau Rezki <urezki@...il.com>
To:     Baoquan He <bhe@...hat.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 06/07/22 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.

-- 
Uladzislau Rezki