linux-kernel - Re: [PATCH] mm, memory_hotplug: Fix the wrong usage of N_HIGH

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20190320093740.GH30433@dhcp22.suse.cz>
Date:   Wed, 20 Mar 2019 10:37:40 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Baoquan He <bhe@...hat.com>
Cc:     linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
        osalvador@...e.de, david@...hat.com, richard.weiyang@...il.com,
        rppt@...ux.ibm.com
Subject: Re: [PATCH] mm, memory_hotplug: Fix the wrong usage of N_HIGH_MEMORY

On Wed 20-03-19 17:06:24, Baoquan He wrote:
> On 03/20/19 at 09:46am, Michal Hocko wrote:
> > On Wed 20-03-19 16:07:32, Baoquan He wrote:
> > > In function node_states_check_changes_online(), N_HIGH_MEMORY is used
> > > to substitute ZONE_HIGHMEM directly. This is not right. N_HIGH_MEMORY
> > > always has value '3' if CONFIG_HIGHMEM=y, while ZONE_HIGHMEM's value
> > > is not. It depends on whether CONFIG_ZONE_DMA/CONFIG_ZONE_DMA32 are
> > > enabled. Obviously it's not true for CONFIG_ZONE_DMA32 on 32bit system,
> > > and CONFIG_ZONE_DMA is also optional.
> > > 
> > > Replace it with ZONE_HIGHMEM.
> > 
> > N*MEMORY is confusing as hell but I am really curious whether we have
> > ZONE_DMA32 and ZONE_HIGMEM together?
> 
> Not sure. AFAIK, on x86_32 it can't be.
> 
> > 
> > That being said N.*MEMORY is intended to check for nodes rather than
> > zones so the patch looks good to me but I think the above explanation is
> > misleading and will add even more mud to the picture when somebody tries
> > to understand what the heck is going on here.
> 
> Yes, agree. I also thought this again after I sent out patch, feel log is not
> good. As you said, they are value of enum node_states and enum zone_type
> separately.
> 
> How about this:
> 
> ~~~
> In function node_states_check_changes_online(), N_HIGH_MEMORY is used
> to substitute ZONE_HIGHMEM directly. This is not right. N_HIGH_MEMORY
> is to mark the memory state of node. Here zone index is checked, which
> should be compared with 'ZONE_HIGHMEM' accordingly.
> 
> Replace it with ZONE_HIGHMEM.

OK, this is better. Thanks!

Feel free to stamp the patch with
Acked-by: Michal Hocko <mhocko@...e.com>

-- 
Michal Hocko
SUSE Labs