linux-kernel - Re: [PATCH] selftests: proc: Make sure wchan works when it exists

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Message-ID: <202110211310.634B74A@keescook>
Date:   Thu, 21 Oct 2021 13:12:29 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Andy Lutomirski <luto@...nel.org>
Cc:     "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Mark Rutland <mark.rutland@....com>,
        Shuah Khan <shuah@...nel.org>,
        Alexey Dobriyan <adobriyan@...il.com>,
        linux-kselftest@...r.kernel.org,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Alexey Gladkov <gladkov.alexey@...il.com>,
        Jann Horn <jannh@...gle.com>,
        Vito Caputo <vcaputo@...garu.com>,
        Ingo Molnar <mingo@...hat.com>, juri.lelli@...hat.com,
        vincent.guittot@...aro.org, dietmar.eggemann@....com,
        Steven Rostedt <rostedt@...dmis.org>,
        Ben Segall <bsegall@...gle.com>, mgorman@...e.de,
        bristot@...hat.com,
        Christian Brauner <christian.brauner@...ntu.com>,
        amistry@...gle.com, Kenta.Tada@...y.com, legion@...nel.org,
        michael.weiss@...ec.fraunhofer.de, Michal Hocko <mhocko@...e.com>,
        deller@....de, Qi Zheng <zhengqi.arch@...edance.com>, me@...in.cc,
        tycho@...ho.pizza, Thomas Gleixner <tglx@...utronix.de>,
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        vgupta@...nel.org, "Russell King (Oracle)" <linux@...linux.org.uk>,
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        bcain@...eaurora.org, monstr@...str.eu, tsbogend@...ha.franken.de,
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        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-fsdevel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH] selftests: proc: Make sure wchan works when it exists

On Thu, Oct 21, 2021 at 01:03:33PM -0700, Andy Lutomirski wrote:
> 
> 
> On Fri, Oct 8, 2021, at 4:55 PM, Kees Cook wrote:
> > This makes sure that wchan contains a sensible symbol when a process is
> > blocked. Specifically this calls the sleep() syscall, and expects the
> > architecture to have called schedule() from a function that has "sleep"
> > somewhere in its name. For example, on the architectures I tested
> > (x86_64, arm64, arm, mips, and powerpc) this is "hrtimer_nanosleep":
> 
> Is this really better than admitting that the whole mechanism is nonsense and disabling it?
> 
> We could have a fixed string for each task state and call it a day.

I consider this to be "future work". In earlier discussions it came up,
but there wasn't an obvious clean cost-free way to do this, so instead
we're just fixing the broken corner and keeping the mostly working rest
of it while cleaning up the weird edges. :)

-- 
Kees Cook