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[156.34.48.30]) by smtp.gmail.com with ESMTPSA id y13sm204954qto.23.2020.06.17.08.29.41 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 17 Jun 2020 08:29:41 -0700 (PDT) Received: from jgg by mlx with local (Exim 4.93) (envelope-from ) id 1jla0S-009d9h-Uc; Wed, 17 Jun 2020 12:29:40 -0300 Date: Wed, 17 Jun 2020 12:29:40 -0300 From: Jason Gunthorpe To: Daniel Vetter Cc: Thomas =?utf-8?B?SGVsbHN0csO2bSAoSW50ZWwp?= , DRI Development , linux-rdma , Intel Graphics Development , Maarten Lankhorst , LKML , amd-gfx list , "moderated list:DMA BUFFER SHARING FRAMEWORK" , Thomas Hellstrom , Daniel Vetter , "open list:DMA BUFFER SHARING FRAMEWORK" , Christian =?utf-8?B?S8O2bmln?= , Mika Kuoppala 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> <20200611083430.GD20149@phenom.ffwll.local> <20200611141515.GW6578@ziepe.ca> <20200616120719.GL20149@phenom.ffwll.local> <20200616145312.GC6578@ziepe.ca> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: linux-rdma-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-rdma@vger.kernel.org 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