From mboxrd@z Thu Jan  1 00:00:00 1970
Return-path: <linux-media-owner@vger.kernel.org>
Received: from mga04.intel.com ([192.55.52.120]:56177 "EHLO mga04.intel.com"
        rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP
        id S1750715AbdI2MeY (ORCPT <rfc822;linux-media@vger.kernel.org>);
        Fri, 29 Sep 2017 08:34:24 -0400
Message-ID: <1506688459.4729.88.camel@linux.intel.com>
Subject: Re: [PATCH] dma-fence: fix dma_fence_get_rcu_safe
From: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
To: Daniel Vetter <daniel@ffwll.ch>,
        Christian =?ISO-8859-1?Q?K=F6nig?= <christian.koenig@amd.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>,
        Daniel Vetter <daniel.vetter@ffwll.ch>,
        Sumit Semwal <sumit.semwal@linaro.org>,
        "linux-media@vger.kernel.org" <linux-media@vger.kernel.org>,
        dri-devel <dri-devel@lists.freedesktop.org>,
        "linaro-mm-sig@lists.linaro.org" <linaro-mm-sig@lists.linaro.org>,
        Maarten Lankhorst <maarten.lankhorst@linux.intel.com>,
        Gustavo Padovan <gustavo@padovan.org>,
        Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>,
        Chris Wilson <chris@chris-wilson.co.uk>
Date: Fri, 29 Sep 2017 15:34:19 +0300
In-Reply-To: <CAKMK7uGkEFzbrhAS1qWs-g3dC20jubXitR5ALkTg4PhMwoQ-Rg@mail.gmail.com>
References: <1504531653-13779-1-git-send-email-deathsimple@vodafone.de>
         <150453243791.23157.6907537389223890207@mail.alporthouse.com>
         <67fe7e05-7743-40c8-558b-41b08eb986e9@amd.com>
         <150512037119.16759.472484663447331384@mail.alporthouse.com>
         <3c412ee3-854a-292a-e036-7c5fd7888979@amd.com>
         <150512178199.16759.73667469529688@mail.alporthouse.com>
         <5ff4b100-b580-a93d-aa5e-c66173ac091d@amd.com>
         <150512410278.16759.10537429613477592631@mail.alporthouse.com>
         <79e447f8-f2e3-57e3-b5fe-503e5feb2f82@amd.com>
         <CAKMK7uGkEFzbrhAS1qWs-g3dC20jubXitR5ALkTg4PhMwoQ-Rg@mail.gmail.com>
Content-Type: text/plain; charset="UTF-8"
Mime-Version: 1.0
Content-Transfer-Encoding: 8bit
Sender: linux-media-owner@vger.kernel.org
List-ID: <linux-media.vger.kernel.org>

On Wed, 2017-09-20 at 20:20 +0200, Daniel Vetter wrote:
> On Mon, Sep 11, 2017 at 01:06:32PM +0200, Christian König wrote:
> > Am 11.09.2017 um 12:01 schrieb Chris Wilson:
> > > [SNIP]
> > > > Yeah, but that is illegal with a fence objects.
> > > > 
> > > > When anybody allocates fences this way it breaks at least
> > > > reservation_object_get_fences_rcu(),
> > > > reservation_object_wait_timeout_rcu() and
> > > > reservation_object_test_signaled_single().
> > > 
> > > Many, many months ago I sent patches to fix them all.
> > 
> > Found those after a bit a searching. Yeah, those patches where proposed more
> > than a year ago, but never pushed upstream.
> > 
> > Not sure if we really should go this way. dma_fence objects are shared
> > between drivers and since we can't judge if it's the correct fence based on
> > a criteria in the object (only the read counter which is outside) all
> > drivers need to be correct for this.
> > 
> > I would rather go the way and change dma_fence_release() to wrap
> > fence->ops->release into call_rcu() to keep the whole RCU handling outside
> > of the individual drivers.
> 
> Hm, I entirely dropped the ball on this, I kinda assumed that we managed
> to get some agreement on this between i915 and dma_fence. Adding a pile
> more people.
> 
> Joonas, Tvrtko, I guess we need to fix this one way or the other.

I definitely didn't get the memo or notice this before. Tvrtko/Chris?

Regars, Joonas
-- 
Joonas Lahtinen
Open Source Technology Center
Intel Corporation