linux-kernel - Re: [PATCH v3 07/13] futex: Throughput-optimized (TP) futexes

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Date:   Sat, 1 Oct 2016 08:47:31 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Waiman Long <Waiman.Long@....com>
cc:     Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Jonathan Corbet <corbet@....net>, linux-kernel@...r.kernel.org,
        linux-doc@...r.kernel.org,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Davidlohr Bueso <dave@...olabs.net>,
        Mike Galbraith <umgwanakikbuti@...il.com>,
        Jason Low <jason.low2@....com>,
        Scott J Norton <scott.norton@....com>,
        Douglas Hatch <doug.hatch@....com>
Subject: Re: [PATCH v3 07/13] futex: Throughput-optimized (TP) futexes

On Fri, 30 Sep 2016, Waiman Long wrote:
> +	WRITE_ONCE(state->owner, current);
> +	preempt_disable();
> +	for (;;) {
> +		ret = futex_trylock(uaddr, vpid, &uval, true);

Did you actually read what I said? You CANNOT access userspace in a preempt
disabled region without disabling pagefaults and handle the resulting
wreckage yourself.

End of review.

       tglx