Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Date:   Wed, 17 Jun 2020 12:29:40 -0300
From:   Jason Gunthorpe <jgg@ziepe.ca>
To:     Daniel Vetter <daniel@ffwll.ch>
Cc:     Thomas =?utf-8?B?SGVsbHN0csO2bSAoSW50ZWwp?= 
        <thomas_os@shipmail.org>,
        DRI Development <dri-devel@lists.freedesktop.org>,
        linux-rdma <linux-rdma@vger.kernel.org>,
        Intel Graphics Development <intel-gfx@lists.freedesktop.org>,
        Maarten Lankhorst <maarten.lankhorst@linux.intel.com>,
        LKML <linux-kernel@vger.kernel.org>,
        amd-gfx list <amd-gfx@lists.freedesktop.org>,
        "moderated list:DMA BUFFER SHARING FRAMEWORK" 
        <linaro-mm-sig@lists.linaro.org>,
        Thomas Hellstrom <thomas.hellstrom@intel.com>,
        Daniel Vetter <daniel.vetter@intel.com>,
        "open list:DMA BUFFER SHARING FRAMEWORK" 
        <linux-media@vger.kernel.org>,
        Christian =?utf-8?B?S8O2bmln?= <christian.koenig@amd.com>,
        Mika Kuoppala <mika.kuoppala@intel.com>
Subject: Re: [Linaro-mm-sig] [PATCH 04/18] dma-fence: prime lockdep
 annotations
Message-ID: <20200617152940.GG6578@ziepe.ca>
References: <20200604081224.863494-1-daniel.vetter@ffwll.ch>
 <20200604081224.863494-5-daniel.vetter@ffwll.ch>
 <b11c2140-1b9c-9013-d9bb-9eb2c1906710@shipmail.org>
 <20200611083430.GD20149@phenom.ffwll.local>
 <20200611141515.GW6578@ziepe.ca>
 <20200616120719.GL20149@phenom.ffwll.local>
 <20200616145312.GC6578@ziepe.ca>
 <CAKMK7uER6ax1zr14xYLKqDfDZp+ycBsY9Yx7JaVkKQ849VfSPg@mail.gmail.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <CAKMK7uER6ax1zr14xYLKqDfDZp+ycBsY9Yx7JaVkKQ849VfSPg@mail.gmail.com>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Wed, Jun 17, 2020 at 09:57:54AM +0200, Daniel Vetter wrote:

> > At the very least I think there should be some big warning that
> > dma_fence in notifiers should be avoided.
> 
> Yeah I'm working on documentation, and also the notifiers here
> hopefully make it clear it's massive pain. I think we could even make
> a hard rule that dma_fence in mmu notifier outside of drivers/gpu is a
> bug/misfeature.

Yep!
 
> Might be a good idea to add a MAINTAINERS entry with a K: regex
> pattern, so that you can catch such modifiers. We do already have such
> a pattern for dma-fence, to catch abuse. So if you want I could type
> up a documentation patch for this, get your and others acks and the
> dri-devel folks would enforce that the dma_fence_wait madness doesn't
> leak beyond drivers/gpu

It seems like the best thing
 
> Oded has agreed to remove the dma-fence usage, since they really don't
> need it (and all the baggage that comes with it), plain old completion
> is enough for their use. This use is also why I added the regex to
> MAINTAINERS, so that in the future we can catch people who try to use
> dma_fence because it looks cute and useful, and are completely
> oblivious to all the pain and headaches involved.

This is good!

Thanks,
Jason