From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id E7A2BC32793 for ; Wed, 24 Aug 2022 15:49:38 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237876AbiHXPth (ORCPT ); Wed, 24 Aug 2022 11:49:37 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:43328 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S236868AbiHXPtg (ORCPT ); Wed, 24 Aug 2022 11:49:36 -0400 Received: from madras.collabora.co.uk (madras.collabora.co.uk [46.235.227.172]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 247D061717; Wed, 24 Aug 2022 08:49:35 -0700 (PDT) Received: from [192.168.2.145] (109-252-119-13.nat.spd-mgts.ru [109.252.119.13]) (using TLSv1.3 with cipher TLS_AES_128_GCM_SHA256 (128/128 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits)) (No client certificate requested) (Authenticated sender: dmitry.osipenko) by madras.collabora.co.uk (Postfix) with ESMTPSA id 003536601DAD; Wed, 24 Aug 2022 16:49:30 +0100 (BST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=collabora.com; s=mail; t=1661356173; bh=vOJMhTQ7HzZBp0ZZo9K4hrXQVabXIso7oNLwG6hsKLo=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=c6s4L7HIzhqXHIRjPO78mUx2njs0FTSDwh/if1G8GrYUXKIesr5TSuVpzCCXzCFaC RQwFs9mzKIF/SoKOeW/iFsEtF2HNDrH0QYgFH8Bjb0EODV2gEnzbMJNa3D7Euz+aq1 ttSiIgN9lBknJRw6hrDsumfPw8z1mfE/u3dAN4OYGFY1SnY5ytLPSVBmnTh6lKyQde YOUN/UNH4qT1TRrXxpbCLStfVkyl6+y4obXi9sfi44ZsbJWXBmSFG438Hbbw7Cm9FD zamHCbpRiEHeEJEqGHwgMIgiFMUhzX7OjakAgX0Hfj9WgvOsPDRnfMMAi2GCcW6bPu eS/kqb6U0BR1g== Message-ID: <25d6b7e7-bbcc-7613-42d1-13c2b9ab2937@collabora.com> Date: Wed, 24 Aug 2022 18:49:28 +0300 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.12.0 Subject: Re: [Linaro-mm-sig] [PATCH v3 6/9] dma-buf: Move dma-buf attachment to dynamic locking specification Content-Language: en-US To: =?UTF-8?Q?Christian_K=c3=b6nig?= , David Airlie , Gerd Hoffmann , Gurchetan Singh , Chia-I Wu , Daniel Vetter , Daniel Almeida , Gert Wollny , Gustavo Padovan , Daniel Stone , Tomeu Vizoso , Maarten Lankhorst , Maxime Ripard , Thomas Zimmermann , Rob Clark , Sumit Semwal , =?UTF-8?Q?Christian_K=c3=b6nig?= , "Pan, Xinhui" , Thierry Reding , Tomasz Figa , Marek Szyprowski , Mauro Carvalho Chehab , Alex Deucher , Jani Nikula , Joonas Lahtinen , Rodrigo Vivi , Tvrtko Ursulin , =?UTF-8?Q?Thomas_Hellstr=c3=b6m?= , Qiang Yu Cc: dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org, Dmitry Osipenko , linux-media@vger.kernel.org, linaro-mm-sig@lists.linaro.org, amd-gfx@lists.freedesktop.org, intel-gfx@lists.freedesktop.org, kernel@collabora.com, virtualization@lists.linux-foundation.org, linux-rdma@vger.kernel.org, linux-arm-msm@vger.kernel.org, lima@lists.freedesktop.org References: <20220824102248.91964-1-dmitry.osipenko@collabora.com> <20220824102248.91964-7-dmitry.osipenko@collabora.com> <055c3c05-ac4c-430e-f2b9-08f000acf435@gmail.com> From: Dmitry Osipenko In-Reply-To: <055c3c05-ac4c-430e-f2b9-08f000acf435@gmail.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-rdma@vger.kernel.org On 8/24/22 18:24, Christian König wrote: > Am 24.08.22 um 12:22 schrieb Dmitry Osipenko: >> Move dma-buf attachment API functions to the dynamic locking >> specification. >> The strict locking convention prevents deadlock situations for dma-buf >> importers and exporters. >> >> Previously, the "unlocked" versions of the attachment API functions >> weren't taking the reservation lock and this patch makes them to take >> the lock. >> >> Intel and AMD GPU drivers already were mapping the attached dma-bufs >> under >> the held lock during attachment, hence these drivers are updated to use >> the locked functions. >> >> Signed-off-by: Dmitry Osipenko >> --- >>   drivers/dma-buf/dma-buf.c                  | 115 ++++++++++++++------- >>   drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c    |   4 +- >>   drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c |   8 +- >>   drivers/gpu/drm/i915/gem/i915_gem_object.c |  12 +++ >>   include/linux/dma-buf.h                    |  20 ++-- >>   5 files changed, 110 insertions(+), 49 deletions(-) >> >> diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c >> index 4556a12bd741..f2a5a122da4a 100644 >> --- a/drivers/dma-buf/dma-buf.c >> +++ b/drivers/dma-buf/dma-buf.c >> @@ -559,7 +559,7 @@ static struct file *dma_buf_getfile(struct dma_buf >> *dmabuf, int flags) >>    * 2. Userspace passes this file-descriptors to all drivers it wants >> this buffer >>    *    to share with: First the file descriptor is converted to a >> &dma_buf using >>    *    dma_buf_get(). Then the buffer is attached to the device using >> - *    dma_buf_attach(). >> + *    dma_buf_attach_unlocked(). > > Now I get why this is confusing me so much. > > The _unlocked postfix implies that there is another function which > should be called with the locks already held, but this is not the case > for attach/detach (because they always need to grab the lock themselves). That's correct. The attach/detach ops of exporter can take the lock (like i915 exporter does it), hence importer must not grab the lock around dma_buf_attach() invocation. > So I suggest to drop the _unlocked postfix for the attach/detach > functions. Another step would then be to unify attach/detach with > dynamic_attach/dynamic_detach when both have the same locking convention > anyway. It's not a problem to change the name, but it's unclear to me why we should do it. The _unlocked postfix tells importer that reservation must be unlocked and it must be unlocked in case of dma_buf_attach(). Dropping the postfix will make dma_buf_attach() inconsistent with the rest of the _unlocked functions(?). Are you sure we need to rename it? > Sorry that this is going so much back and forth, it's really complicated > to keep all the stuff in my head at the moment :) Not a problem at all, I expected that it will take some time for this patchset to settle down. -- Best regards, Dmitry