linux-kernel - Re: [PATCH -v6 12/13] futex: futex_unlock

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Date:   Fri, 7 Apr 2017 18:27:07 -0700
From:   Darren Hart <dvhart@...radead.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     tglx@...utronix.de, mingo@...nel.org, juri.lelli@....com,
        rostedt@...dmis.org, xlpang@...hat.com, bigeasy@...utronix.de,
        linux-kernel@...r.kernel.org, mathieu.desnoyers@...icios.com,
        jdesfossez@...icios.com, bristot@...hat.com
Subject: Re: [PATCH -v6 12/13] futex: futex_unlock_pi() determinism

On Wed, Mar 22, 2017 at 11:35:59AM +0100, Peter Zijlstra wrote:
> The problem with returning -EAGAIN when the waiter state mismatches is
> that it becomes very hard to proof a bounded execution time on the

prove

> operation. And seeing that this is a RT operation, this is somewhat

an RT

> important.
> 
> While in practise; given the previous patch; it will be very unlikely

Heh, that's not what semicolons are for ;-) Commas here, or a parenthetical.

> to ever really take more than one or two rounds, proving so becomes
> rather hard.
> 
> However, now that modifying wait_list is done while holding both
> hb->lock and wait_lock, we can avoid the scenario entirely if we
> acquire wait_lock while still holding hb-lock. Doing a hand-over,
> without leaving a hole.

Nice :)

-- 
Darren Hart
VMware Open Source Technology Center