linux-kernel - Re: [PATCH] mm, oom: initiallize all new zap

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Message-ID: <5678A001.4040700@oracle.com>
Date:	Mon, 21 Dec 2015 19:57:37 -0500
From:	Sasha Levin <sasha.levin@...cle.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	"Kirill A. Shutemov" <kirill@...temov.name>, mhocko@...e.com,
	mgorman@...e.de, linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm, oom: initiallize all new zap_details fields before
 use

On 12/21/2015 05:24 PM, Andrew Morton wrote:
>>> Should we use c99 initializer instead to make it future-proof?
>> > 
>> > I didn't do that to make these sort of failures obvious. In this case, if we would have
>> > used an initializer and it would default to the "wrong" values it would be much harder
>> > to find this bug.
>> > 
> If we're to make that approach useful and debuggable we should poison
> the structure at the outset with some well-known and crazy pattern.  Or
> use kasan.

We sort of do. Consider stack garbage as "poison"...

This bug was found using UBSan which complained that a bool suddenly had the
value of '64'.

If we go back to the scenario I've described, and the struct would have been
initialized on declaration, you'd have a much harder time finding it rather
than letting our existing and future tools find it.


Thanks,
Sasha
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