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From:   Yang Shi <shy828301@gmail.com>
Date:   Tue, 5 Jan 2021 09:14:11 -0800
Message-ID: <CAHbLzkoN3bdnHa-xOmGWQhN+dw7AQtbwygsH=VS5or=QoBk0Jg@mail.gmail.com>
Subject: Re: [PATCH] mm: migrate: initialize err in do_migrate_pages
To:     Jan Stancek <jstancek@redhat.com>
Cc:     Linux MM <linux-mm@kvack.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Zi Yan <ziy@nvidia.com>, Jan Kara <jack@suse.cz>,
        Matthew Wilcox <willy@infradead.org>,
        Mel Gorman <mgorman@suse.de>, Michal Hocko <mhocko@suse.com>,
        Song Liu <songliubraving@fb.com>,
        Andrew Morton <akpm@linux-foundation.org>
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On Tue, Jan 5, 2021 at 6:14 AM Jan Stancek <jstancek@redhat.com> wrote:
>
> After commit 236c32eb1096 ("mm: migrate: clean up migrate_prep{_local}")',
> do_migrate_pages can return uninitialized variable 'err' (which is
> propagated to user-space as error) when 'from' and 'to' nodesets
> are identical. This can be reproduced with LTP migrate_pages01,
> which calls migrate_pages() with same set for both old/new_nodes.
>
> Add 'err' initialization back.

Thanks for catching this. Acked-by: Yang Shi <shy828301@gmail.com>

>
> Fixes: 236c32eb1096 ("mm: migrate: clean up migrate_prep{_local}")
> Cc: Zi Yan <ziy@nvidia.com>
> Cc: Yang Shi <shy828301@gmail.com>
> Cc: Jan Kara <jack@suse.cz>
> Cc: Matthew Wilcox <willy@infradead.org>
> Cc: Mel Gorman <mgorman@suse.de>
> Cc: Michal Hocko <mhocko@suse.com>
> Cc: Song Liu <songliubraving@fb.com>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Signed-off-by: Jan Stancek <jstancek@redhat.com>
> ---
>  mm/mempolicy.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/mm/mempolicy.c b/mm/mempolicy.c
> index 8cf96bd21341..2c3a86502053 100644
> --- a/mm/mempolicy.c
> +++ b/mm/mempolicy.c
> @@ -1111,7 +1111,7 @@ int do_migrate_pages(struct mm_struct *mm, const nodemask_t *from,
>                      const nodemask_t *to, int flags)
>  {
>         int busy = 0;
> -       int err;
> +       int err = 0;
>         nodemask_t tmp;
>
>         migrate_prep();
> --
> 2.18.1
>