linux-kernel - Re: [PATCH v1 1/1] mm: buddy page accessed before initialized

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Message-ID: <20171103085958.pewhlyvkr5oa2fgf@dhcp22.suse.cz>
Date:   Fri, 3 Nov 2017 09:59:58 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Pavel Tatashin <pasha.tatashin@...cle.com>
Cc:     steven.sistare@...cle.com, daniel.m.jordan@...cle.com,
        akpm@...ux-foundation.org, mgorman@...hsingularity.net,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1 1/1] mm: buddy page accessed before initialized

On Thu 02-11-17 12:10:39, Pavel Tatashin wrote:
> > > 
> > > Yes, but as I said, unfortunately memset(1) with CONFIG_VM_DEBUG does not
> > > catch this case. So, when CONFIG_VM_DEBUG is enabled kexec reboots without
> > > issues.
> > 
> > Can we make the init pattern to catch this?
> 
> Unfortunately, that is not easy: memset() gives us only one byte to play
> with, and if we use something else that will make CONFIG_VM_DEBUG
> unacceptably slow.

Why cannot we do something similar to the optimized struct page
initialization and write 8B at the time and fill up the size unaligned
chunk in 1B?
-- 
Michal Hocko
SUSE Labs