linux-kernel - Re: [Regression] stress-ng udp-flood causes kernel panic on Ampere Altra

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Message-ID: <20220706124007.GB7996@breakpoint.cc>
Date:   Wed, 6 Jul 2022 14:40:07 +0200
From:   Florian Westphal <fw@...len.de>
To:     Will Deacon <will@...nel.org>
Cc:     Florian Westphal <fw@...len.de>,
        Kajetan Puchalski <kajetan.puchalski@....com>,
        Pablo Neira Ayuso <pablo@...filter.org>,
        Jozsef Kadlecsik <kadlec@...filter.org>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>, Mel Gorman <mgorman@...e.de>,
        lukasz.luba@....com, dietmar.eggemann@....com,
        mark.rutland@....com, broonie@...nel.org,
        netfilter-devel@...r.kernel.org, coreteam@...filter.org,
        netdev@...r.kernel.org, stable@...r.kernel.org,
        regressions@...ts.linux.dev, linux-kernel@...r.kernel.org,
        peterz@...radead.org
Subject: Re: [Regression] stress-ng udp-flood causes kernel panic on Ampere
 Altra

Will Deacon <will@...nel.org> wrote:
> On Wed, Jul 06, 2022 at 02:02:01PM +0200, Florian Westphal wrote:
> > +	/* ->status and ->timeout loads must happen after refcount increase */
> > +	smp_rmb();
> 
> Sorry I didn't suggest this earlier, but if all of these smp_rmb()s are
> for upgrading the ordering from refcount_inc_not_zero() then you should
> use smp_acquire__after_ctrl_dep() instead. It's the same under the hood,
> but it illustrates what's going on a bit better.

Ok, I can replace it and send a v2, no problem.