linux-kernel - Re: [PATCH v2 1/2] locking: Implement an algorithm choice for Wound-Wait mutexes

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Message-ID: <20180614144659.GC12198@hirez.programming.kicks-ass.net>
Date:   Thu, 14 Jun 2018 16:46:59 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Thomas Hellstrom <thellstrom@...are.com>
Cc:     Matthew Wilcox <willy@...radead.org>,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        Ingo Molnar <mingo@...hat.com>,
        Jonathan Corbet <corbet@....net>,
        Gustavo Padovan <gustavo@...ovan.org>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Sean Paul <seanpaul@...omium.org>,
        David Airlie <airlied@...ux.ie>,
        Davidlohr Bueso <dave@...olabs.net>,
        "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
        Josh Triplett <josh@...htriplett.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Kate Stewart <kstewart@...uxfoundation.org>,
        Philippe Ombredanne <pombredanne@...b.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-doc@...r.kernel.org, linux-media@...r.kernel.org,
        linaro-mm-sig@...ts.linaro.org
Subject: Re: [PATCH v2 1/2] locking: Implement an algorithm choice for
 Wound-Wait mutexes

On Thu, Jun 14, 2018 at 03:43:04PM +0200, Thomas Hellstrom wrote:
> It's intended to be enforced by storing the algorithm choice in the
> WW_MUTEX_CLASS which must be common for an acquire context and the
> ww_mutexes it acquires. However, I don't think there is a check that that
> holds. I guess we could add it as a DEBUG_MUTEX test in ww_mutex_lock().

There is ww_mutex_lock_acquired():

	DEBUG_LOCKS_WARN_ON(ww_ctx->ww_class != ww->ww_class)

which should trigger if you try and be clever.