linux-kernel - Re: [PATCH V2] mm: fix potential pte_unmap

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Message-ID: <ed500ac7-0b67-cde1-57dc-ca7347fd8560@huawei.com>
Date:   Mon, 19 Oct 2020 15:25:13 +0800
From:   Shijie Luo <luoshijie1@...wei.com>
To:     Michal Hocko <mhocko@...e.com>
CC:     <akpm@...ux-foundation.org>, <linux-mm@...ck.org>,
        <linux-kernel@...r.kernel.org>, <osalvador@...e.de>,
        <linmiaohe@...wei.com>, <linfeilong@...wei.com>
Subject: Re: [PATCH V2] mm: fix potential pte_unmap_unlock pte error

On 2020/10/19 14:59, Michal Hocko wrote:
> On Fri 16-10-20 22:11:51, 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.
> This would really benefit from some improvements. It is preferable to
> provide a user visibile effect of the patch. I would propose this, feel
> free to reuse parts as you find fit.
> "
> queue_pages_pte_range can run in MPOL_MF_MOVE_ALL mode which doesn't
> migrate misplaced pages but returns with EIO when encountering such a
> page. Since a7f40cfe3b7a ("mm: mempolicy: make mbind() return -EIO when
> MPOL_MF_STRICT is specified") and early break on the first pte in the
> range results in pte_unmap_unlock on an underflow pte. This can lead to
> lockups later on when somebody tries to lock the pte resp.
> page_table_lock again..
>
> Fixes: a7f40cfe3b7a ("mm: mempolicy: make mbind() return -EIO when
> MPOL_MF_STRICT is specified")
> "
I will take these in my patch description and send version 3, Thanks.