Date: Sat, 26 May 2018 14:44:31 -0500 From: Eric van Gyzen <eric@vangyzen.net> To: Gleb Smirnoff <glebius@FreeBSD.org>, Mateusz Guzik <mjguzik@gmail.com> Cc: "Jonathan T. Looney" <jtl@freebsd.org>, Matthew Macy <mmacy@freebsd.org>, John Baldwin <jhb@freebsd.org>, src-committers <src-committers@freebsd.org>, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: Re: svn commit: r334104 - in head/sys: netinet sys Message-ID: <954ca6de-43dd-af9a-2ab1-2786473de611@vangyzen.net> In-Reply-To: <20180524044746.GX71675@FreeBSD.org> References: <201805231700.w4NH05hs047395@repo.freebsd.org> <2281830.zrSQodBeDb@ralph.baldwin.cx> <CAPrugNo8_h5jnn2Yt250ZH1crwxHhK46QK1vfdyWssYjuuSAqQ@mail.gmail.com> <CADrOrmtmSYtMt4vrqdFHrLqAArBaws8bAeynPa8X_sz7ui86uw@mail.gmail.com> <CAGudoHFi6T3tNCy8NUq=oF6h_4=i0cc3peiD%2BE5-NRYKQZX9Tg@mail.gmail.com> <20180524044746.GX71675@FreeBSD.org>
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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
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