linux-kernel - Re: [PATCH 1/1] futex: futex_wake_op, fix sign

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Message-ID: <CA+55aFw9kwnhBK2jeLX=rby+w8mBgn+gtfQw5NMzfsurimQ4Nw@mail.gmail.com>
Date:   Sun, 10 Dec 2017 12:50:18 -0800
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Jiri Slaby <jslaby@...e.cz>
Cc:     Ingo Molnar <mingo@...hat.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Darren Hart <dvhart@...radead.org>
Subject: Re: [PATCH 1/1] futex: futex_wake_op, fix sign_extend32 sign bits

On Thu, Nov 30, 2017 at 6:35 AM, Jiri Slaby <jslaby@...e.cz> wrote:
> sign_extend32 counts the sign bit parameter from 0, not from 1. So we
> have to use "11" for 12th bit, not "12".

This interface is crap. It really doesn't make much sense. I wonder
how many people have gotten this wrong, but it's hard to tell.

I'm applying this directly to my tree since I didn't see anybody else
react to it, but the whole pattern worries me.

Also, clearly nobody actually uses the odder corners of futex ops
anyway. Maybe we should deprecate them entirely?

Jiri, did you notice by testing, or what?

      Linus