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(unknown [109.252.125.248]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) (Authenticated sender: dmitry.osipenko) by madras.collabora.co.uk (Postfix) with ESMTPSA id EAFB666022C7; Wed, 28 Sep 2022 20:18:21 +0100 (BST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=collabora.com; s=mail; t=1664392705; bh=fZnTUTQr3QLzm0jtSttVhNcnfmXvbA4RmJRVMLoWphc=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=IkR+QrnUT3c5KaLxBLm0AqA2EcE7+Jt+7LjK9vj1hVcTk2com126ETRais472fahl VKhiayGfuFsb27rqSLCaPH+84Qw0yo3MgA3+8xE6sIlcjd/C7+V15lOp6CbDoxxxhD Xg4bR/B5aMaAHznlSfEWbV7UO079mico9ojj3GIfG1FBiC5fTbMaCgkOwVyjabbr58 ED1IBiL39HeivVtumy5sbNgRqV6sVNMCX2TiLUhxysjgvyhGqOb+Nqwxo7p45kFPJs m3zQfKgGNAc2/9Z51l2/22tF6uyhaZPPEq8fwjZu/zQ9urABN15JDPXrRLrXlqZHYa bFg30Vpzg2+rQ== From: Dmitry Osipenko To: 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?= =?utf-8?q?=C3=B6m?= , Qiang Yu , Srinivas Kandagatla , Amol Maheshwari , Jason Gunthorpe , Leon Romanovsky , Juergen Gross , Stefano Stabellini , Oleksandr Tyshchenko , Tomi Valkeinen , Russell King , Lucas Stach , Christian Gmeiner , Ruhl Michael J 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 Subject: [PATCH v6 19/21] dma-buf: Document dynamic locking convention Date: Wed, 28 Sep 2022 22:15:58 +0300 Message-Id: <20220928191600.5874-20-dmitry.osipenko@collabora.com> X-Mailer: git-send-email 2.37.3 In-Reply-To: <20220928191600.5874-1-dmitry.osipenko@collabora.com> References: <20220928191600.5874-1-dmitry.osipenko@collabora.com> MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-media@vger.kernel.org Add documentation for the dynamic locking convention. The documentation tells dma-buf API users when they should take the reservation lock and when not. Acked-by: Sumit Semwal Reviewed-by: Christian König Signed-off-by: Dmitry Osipenko --- Documentation/driver-api/dma-buf.rst | 6 +++ drivers/dma-buf/dma-buf.c | 64 ++++++++++++++++++++++++++++ 2 files changed, 70 insertions(+) diff --git a/Documentation/driver-api/dma-buf.rst b/Documentation/driver-api/dma-buf.rst index 36a76cbe9095..622b8156d212 100644 --- a/Documentation/driver-api/dma-buf.rst +++ b/Documentation/driver-api/dma-buf.rst @@ -119,6 +119,12 @@ DMA Buffer ioctls .. kernel-doc:: include/uapi/linux/dma-buf.h +DMA-BUF locking convention +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +.. kernel-doc:: drivers/dma-buf/dma-buf.c + :doc: locking convention + Kernel Functions and Structures Reference ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c index 2452b4c82584..e04d504441a5 100644 --- a/drivers/dma-buf/dma-buf.c +++ b/drivers/dma-buf/dma-buf.c @@ -795,6 +795,70 @@ static struct sg_table * __map_dma_buf(struct dma_buf_attachment *attach, return sg_table; } +/** + * DOC: locking convention + * + * In order to avoid deadlock situations between dma-buf exports and importers, + * all dma-buf API users must follow the common dma-buf locking convention. + * + * Convention for importers + * + * 1. Importers must hold the dma-buf reservation lock when calling these + * functions: + * + * - dma_buf_pin() + * - dma_buf_unpin() + * - dma_buf_map_attachment() + * - dma_buf_unmap_attachment() + * - dma_buf_vmap() + * - dma_buf_vunmap() + * + * 2. Importers must not hold the dma-buf reservation lock when calling these + * functions: + * + * - dma_buf_attach() + * - dma_buf_dynamic_attach() + * - dma_buf_detach() + * - dma_buf_export( + * - dma_buf_fd() + * - dma_buf_get() + * - dma_buf_put() + * - dma_buf_mmap() + * - dma_buf_begin_cpu_access() + * - dma_buf_end_cpu_access() + * - dma_buf_map_attachment_unlocked() + * - dma_buf_unmap_attachment_unlocked() + * - dma_buf_vmap_unlocked() + * - dma_buf_vunmap_unlocked() + * + * Convention for exporters + * + * 1. These &dma_buf_ops callbacks are invoked with unlocked dma-buf + * reservation and exporter can take the lock: + * + * - &dma_buf_ops.attach() + * - &dma_buf_ops.detach() + * - &dma_buf_ops.release() + * - &dma_buf_ops.begin_cpu_access() + * - &dma_buf_ops.end_cpu_access() + * + * 2. These &dma_buf_ops callbacks are invoked with locked dma-buf + * reservation and exporter can't take the lock: + * + * - &dma_buf_ops.pin() + * - &dma_buf_ops.unpin() + * - &dma_buf_ops.map_dma_buf() + * - &dma_buf_ops.unmap_dma_buf() + * - &dma_buf_ops.mmap() + * - &dma_buf_ops.vmap() + * - &dma_buf_ops.vunmap() + * + * 3. Exporters must hold the dma-buf reservation lock when calling these + * functions: + * + * - dma_buf_move_notify() + */ + /** * dma_buf_dynamic_attach - Add the device to dma_buf's attachments list * @dmabuf: [in] buffer to attach device to.