linux-kernel - Re: [PATCH RFC v2 1/4] mm/mempolicy: Fix get

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Message-ID: <c9b57bde-7834-45c4-2c22-3220e3680c93@huawei.com>
Date:   Wed, 1 Nov 2017 17:37:36 +0800
From:   Yisheng Xie <xieyisheng1@...wei.com>
To:     Vlastimil Babka <vbabka@...e.cz>, <akpm@...ux-foundation.org>,
        <mhocko@...e.com>, <mingo@...nel.org>, <rientjes@...gle.com>,
        <n-horiguchi@...jp.nec.com>, <salls@...ucsb.edu>
CC:     <linux-mm@...ck.org>, <linux-kernel@...r.kernel.org>,
        <tanxiaojun@...wei.com>, <linux-api@...r.kernel.org>,
        Andi Kleen <ak@...ux.intel.com>
Subject: Re: [PATCH RFC v2 1/4] mm/mempolicy: Fix get_nodes() mask
 miscalculation

Hi Vlastimil,

Thanks for comment!
On 2017/10/31 16:34, Vlastimil Babka wrote:
> On 10/27/2017 12:14 PM, Yisheng Xie wrote:
>> It appears there is a nodemask miscalculation in the get_nodes()
>> function in mm/mempolicy.c.  This bug has two effects:
>>
>> 1. It is impossible to specify a length 1 nodemask.
>> 2. It is impossible to specify a nodemask containing the last node.
> 
> This should be more specific, which syscalls are you talking about?
> I assume it's set_mempolicy() and mbind() and it's the same issue that
> was discussed at https://marc.info/?l=linux-mm&m=150732591909576&w=2 ?

I just missed this thread, sorry about that. Not only set_mempolicy() and
mbind(), but migrate_pages() also suffers this problem. Maybe related
manpage should documented this as your mentioned below.

Thanks
Yisheng Xie

> 
>> Brent have submmit a patch before v2.6.12, however, Andi revert his
>> changed for ABI problem. I just resent this patch as RFC, for do not
>> clear about what's the problem Andi have met.
> 
> You should have CC'd Andi. As was discussed in the other thread, this
> would make existing programs potentially unsafe, so we can't change it.
> Instead it should be documented.
> 
>> As manpage of set_mempolicy, If the value of maxnode is zero, the
>> nodemask argument is ignored. but we should not ignore the nodemask
>> when maxnode is 1.
>>