linux-kernel - Re: [PATCH v12 03/12] scs: add support for stack usage debugging

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Message-ID: <20200422235356.GA128062@google.com>
Date:   Wed, 22 Apr 2020 16:53:56 -0700
From:   Sami Tolvanen <samitolvanen@...gle.com>
To:     Will Deacon <will@...nel.org>
Cc:     Catalin Marinas <catalin.marinas@....com>,
        James Morse <james.morse@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Mark Rutland <mark.rutland@....com>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Michal Marek <michal.lkml@...kovi.net>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dave Martin <Dave.Martin@....com>,
        Kees Cook <keescook@...omium.org>,
        Laura Abbott <labbott@...hat.com>,
        Marc Zyngier <maz@...nel.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Jann Horn <jannh@...gle.com>,
        Miguel Ojeda <miguel.ojeda.sandonis@...il.com>,
        clang-built-linux@...glegroups.com,
        kernel-hardening@...ts.openwall.com,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v12 03/12] scs: add support for stack usage debugging

On Wed, Apr 22, 2020 at 06:46:02PM +0100, Will Deacon wrote:
> > +static void scs_check_usage(struct task_struct *tsk)
> > +{
> > +	static unsigned long highest;
> > +	unsigned long used = __scs_used(tsk);
> > +	unsigned long prev;
> > +	unsigned long curr = highest;
> > +
> > +	while (used > curr) {
> > +		prev = cmpxchg(&highest, curr, used);
> 
> I think this can be cmpxchg_relaxed(), since we don't care about ordering
> here afaict.

Sure, I'll change this in v13. Thanks.

Sami