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Subject: Re: svn commit: r334104 - in head/sys: netinet sys
To: Gleb Smirnoff <glebius@FreeBSD.org>, Mateusz Guzik <mjguzik@gmail.com>
Cc: "Jonathan T. Looney" <jtl@freebsd.org>, Matthew Macy <mmacy@freebsd.org>, 
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From: Eric van Gyzen <eric@vangyzen.net>
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Date: Sat, 26 May 2018 14:44:31 -0500
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On 05/23/2018 23:47, Gleb Smirnoff wrote:
> On Thu, May 24, 2018 at 06:44:20AM +0200, Mateusz Guzik wrote:
> M> I fundamentally disagree with this part.
> M>
> M> If a known value of a given field is needed for assertion purposes, you
> M> can add (possibly conditional) code setting this specific value. It
> M> probably should not be zero if it can be helped.
> M>
> M> Conditional zeroing of the *whole* struct depending on invariants will
> M> *hide* uninitialized memory read bugs - production kernel will have
> M> whatever it happens to find, while *debug* kernel will guarantee to
> M> have all the values zeroed. In fact the flag actively combats redzoning.
> M> if the resulting allocation is zeroed, poisoning is actively neutered.
> M> But only if debug is enabled.
> M>
> M> That said, I find the change harmful.
> 
> +1 on fundamentally disagree with M_ZERO_INVARIANTS. It makes the
> INVARIANTS-enabled kernels to crash _later_ than production kernels,
> since instead of uma_junk it places clean zeroes.

Matt,

Mateusz and Gleb raise very good points.  This operates contrary to the 
whole idea of INVARIANTS.  Please revisit this.

Eric