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From: Andy Lutomirski <luto@amacapital.net>
Date: Sun, 3 Apr 2016 06:18:36 -0700
Message-ID: <CALCETrU-SMcGuAGkJGYh-Vu9r3dcDU5hxNVO7GqWrVu1XE6oCQ@mail.gmail.com>
Subject: Re: [RFC patch 4/7] futex: Add support for attached futexes
To: Thomas Gleixner <tglx@linutronix.de>
Cc: Andy Lutomirski <luto@kernel.org>, LKML <linux-kernel@vger.kernel.org>,
        Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
        Darren Hart <darren@dvhart.com>, Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@kernel.org>,
        Michael Kerrisk <mtk.manpages@googlemail.com>,
        Davidlohr Bueso <dave@stgolabs.net>, Chris Mason <clm@fb.com>,
        "Carlos O'Donell" <carlos@redhat.com>,
        Torvald Riegel <triegel@redhat.com>,
        Eric Dumazet <edumazet@google.com>
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On Sun, Apr 3, 2016 at 2:57 AM, Thomas Gleixner <tglx@linutronix.de> wrote:
> On Sat, 2 Apr 2016, Andy Lutomirski wrote:
>
>> On 04/02/2016 04:09 AM, Thomas Gleixner wrote:
>> [omitted due to some Thunderbird bug, sigh]
>>
>> What happens if you mix attached an non-attached ops on the same futex?
>
> Not much. You might get an error code, sleep forever or the call will just
> result in a NOP wasting cpu cycles. That's the same when you mix
> shared/private operations on the same futex.

What's the workflow?

Can the creation of an attached futex fail due to memory allocation
problems or any other reason?  If so, how does a library make sure it
falls back to a normal futex safely?

Why can't private futexes be attached by default?

--Andy