From: osalvador@suse.de
To: Shijie Luo <luoshijie1@huawei.com>
Cc: akpm@linux-foundation.org, linux-mm@kvack.org,
linux-kernel@vger.kernel.org, linmiaohe@huawei.com,
linfeilong@huawei.com
Subject: Re: [PATCH] mm: fix potential pte_unmap_unlock pte error
Date: Thu, 15 Oct 2020 14:58:53 +0200 [thread overview]
Message-ID: <a220bf939f0c9aece318197881d6f092@suse.de> (raw)
In-Reply-To: <20201015121534.50910-1-luoshijie1@huawei.com>
On 2020-10-15 14:15, Shijie Luo wrote:
> When flags don't have MPOL_MF_MOVE or MPOL_MF_MOVE_ALL bits, code
> breaks
> and passing origin pte - 1 to pte_unmap_unlock seems like not a good
> idea.
>
> Signed-off-by: Shijie Luo <luoshijie1@huawei.com>
> Signed-off-by: linmiaohe <linmiaohe@huawei.com>
> ---
> mm/mempolicy.c | 6 +++++-
> 1 file changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/mm/mempolicy.c b/mm/mempolicy.c
> index 3fde772ef5ef..01f088630d1d 100644
> --- a/mm/mempolicy.c
> +++ b/mm/mempolicy.c
> @@ -571,7 +571,11 @@ static int queue_pages_pte_range(pmd_t *pmd,
> unsigned long addr,
> } else
> break;
> }
> - pte_unmap_unlock(pte - 1, ptl);
> +
> + if (addr >= end)
> + pte = pte - 1;
> +
> + pte_unmap_unlock(pte, ptl);
But this is still wrong, isn't it?
Unless I am missing something, this is "only" important under
CONFIG_HIGHPTE.
We have:
pte = pte_offset_map_lock(walk->mm, pmd, addr, &ptl);
which under CONFIG_HIGHPTE does a kmap_atomoc.
Now, we either break the loop in the first pass because of
!(MPOL_MF_MOVE | MPOL_MF_MOVE_ALL),
or we keep incrementing pte by every pass.
Either way is wrong, because the pointer kunmap_atomic gets will not be
the same (since we incremented pte).
Or is the loop meant to be running only once, so pte - 1 will bring us
back to the original pte?
next prev parent reply other threads:[~2020-10-15 12:58 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-10-15 12:15 [PATCH] mm: fix potential pte_unmap_unlock pte error Shijie Luo
2020-10-15 12:58 ` osalvador [this message]
2020-10-15 13:19 ` Shijie Luo
2020-10-16 12:31 ` Michal Hocko
2020-10-16 12:37 ` osalvador
2020-10-16 13:11 ` Michal Hocko
2020-10-16 13:15 ` Michal Hocko
2020-10-16 13:42 ` Michal Hocko
2020-10-16 14:05 ` osalvador
2020-10-17 1:55 ` Shijie Luo
2021-01-09 8:01 [PATCH] mm: Fix " Miaohe Lin
2021-01-10 17:14 ` Andi Kleen
2021-01-14 2:51 ` Miaohe Lin
2021-01-22 8:27 ` Miaohe Lin
2021-01-24 2:01 ` Andrew Morton
2021-01-25 2:04 ` Miaohe Lin
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