linux-kernel - Re: [RFC] nodemask: Consider MAX_NUMNODES inside node

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Message-Id: <6c7ecb18-2ad0-f38a-1dc8-3c6c405b87ce@linux.vnet.ibm.com>
Date:   Tue, 3 Jan 2017 14:37:09 +0530
From:   Anshuman Khandual <khandual@...ux.vnet.ibm.com>
To:     Michal Hocko <mhocko@...nel.org>,
        Anshuman Khandual <khandual@...ux.vnet.ibm.com>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org, vbabka@...e.cz,
        akpm@...ux-foundation.org
Subject: Re: [RFC] nodemask: Consider MAX_NUMNODES inside node_isset

On 01/03/2017 02:14 PM, Michal Hocko wrote:
> On Tue 03-01-17 13:57:53, Anshuman Khandual wrote:
>> node_isset can give incorrect result if the node number is beyond the
>> bitmask size (MAX_NUMNODES in this case) which is not checked inside
>> test_bit. Hence check for the bit limits (MAX_NUMNODES) inside the
>> node_isset function before calling test_bit.
> Could you be more specific when such a thing might happen? Have you seen
> any in-kernel user who would give such a bogus node?

Have not seen this through any in-kernel use case. While rebasing the CDM
zonelist rebuilding series, I came across this through an error path when
a bogus node value of 256 (MAX_NUMNODES on POWER) is received when we call
first_node() on an empty nodemask (which itself seems weird as well).