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Mercier" Date: Wed, 21 Jun 2023 12:24:15 -0700 Message-ID: Subject: Re: [PATCH v4 2/6] dma-buf/heaps: Don't assert held reservation lock for dma-buf mmapping To: Dmitry Osipenko Cc: Sumit Semwal , =?UTF-8?Q?Christian_K=C3=B6nig?= , Benjamin Gaignard , Brian Starkey , John Stultz , Gerd Hoffmann , Daniel Vetter , Jani Nikula , Arnd Bergmann , Thomas Zimmermann , Tomi Valkeinen , Thierry Reding , Tomasz Figa , Marek Szyprowski , Mauro Carvalho Chehab , Emil Velikov , intel-gfx@lists.freedesktop.org, linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org, linux-tegra@vger.kernel.org, kernel@collabora.com, linux-media@vger.kernel.org Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Spam-Status: No, score=-17.6 required=5.0 tests=BAYES_00,DKIMWL_WL_MED, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF, ENV_AND_HDR_SPF_MATCH,RCVD_IN_DNSWL_NONE,SPF_HELO_NONE,SPF_PASS, T_SCC_BODY_TEXT_LINE,USER_IN_DEF_DKIM_WL,USER_IN_DEF_SPF_WL autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Jun 21, 2023 at 11:16=E2=80=AFAM Dmitry Osipenko wrote: > > Hi, > > On 6/21/23 20:21, T.J. Mercier wrote: > > On Mon, May 29, 2023 at 3:46=E2=80=AFPM Dmitry Osipenko > > wrote: > >> > >> Don't assert held dma-buf reservation lock on memory mapping of export= ed > >> buffer. > >> > >> We're going to change dma-buf mmap() locking policy such that exporter= s > >> will have to handle the lock. The previous locking policy caused deadl= ock > >> problem for DRM drivers in a case of self-imported dma-bufs once these > >> drivers are moved to use reservation lock universally. The problem > >> solved by moving the lock down to exporters. This patch prepares dma-b= uf > >> heaps for the locking policy update. > >> > > Hi Dmitry, > > > > I see that in patch 6 of this series calls to > > dma_resv_lock/dma_resv_unlock have been added to the > > drm_gem_shmem_helper functions and some exporters. But I'm curious why > > no dma_resv_lock/dma_resv_unlock calls were added to these two dma-buf > > heap exporters for mmap? > > DMA-buf heaps are exporters, drm_gem_shmem_helper is importer. Locking > rules are different for importers and exporters. > > DMA-heaps use own locking, they can be moved to resv lock in the future. > > DMA-heaps don't protect internal data in theirs mmap() implementations, > nothing to protect there. > Thanks.