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Thu, 25 Jan 2024 09:24:06 -0800 (PST) Date: Thu, 25 Jan 2024 18:24:04 +0100 From: Daniel Vetter To: Dmitry Osipenko Cc: David Airlie , Gerd Hoffmann , Gurchetan Singh , Chia-I Wu , Daniel Vetter , Maarten Lankhorst , Maxime Ripard , Thomas Zimmermann , Christian =?iso-8859-1?Q?K=F6nig?= , Qiang Yu , Steven Price , Boris Brezillon , Emma Anholt , Melissa Wen , dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org, kernel@collabora.com, virtualization@lists.linux-foundation.org Subject: Re: [PATCH v19 09/30] drm/shmem-helper: Add and use lockless drm_gem_shmem_get_pages() Message-ID: Mail-Followup-To: Dmitry Osipenko , David Airlie , Gerd Hoffmann , Gurchetan Singh , Chia-I Wu , Maarten Lankhorst , Maxime Ripard , Thomas Zimmermann , Christian =?iso-8859-1?Q?K=F6nig?= , Qiang Yu , Steven Price , Boris Brezillon , Emma Anholt , Melissa Wen , dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org, kernel@collabora.com, virtualization@lists.linux-foundation.org References: <20240105184624.508603-1-dmitry.osipenko@collabora.com> <20240105184624.508603-10-dmitry.osipenko@collabora.com> Precedence: bulk X-Mailing-List: virtualization@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20240105184624.508603-10-dmitry.osipenko@collabora.com> X-Operating-System: Linux phenom 6.6.11-amd64 On Fri, Jan 05, 2024 at 09:46:03PM +0300, Dmitry Osipenko wrote: > Add lockless drm_gem_shmem_get_pages() helper that skips taking reservation > lock if pages_use_count is non-zero, leveraging from atomicity of the > refcount_t. Make drm_gem_shmem_mmap() to utilize the new helper. > > Acked-by: Maxime Ripard > Reviewed-by: Boris Brezillon > Suggested-by: Boris Brezillon > Signed-off-by: Dmitry Osipenko > --- > drivers/gpu/drm/drm_gem_shmem_helper.c | 19 +++++++++++++++---- > 1 file changed, 15 insertions(+), 4 deletions(-) > > diff --git a/drivers/gpu/drm/drm_gem_shmem_helper.c b/drivers/gpu/drm/drm_gem_shmem_helper.c > index cacf0f8c42e2..1c032513abf1 100644 > --- a/drivers/gpu/drm/drm_gem_shmem_helper.c > +++ b/drivers/gpu/drm/drm_gem_shmem_helper.c > @@ -226,6 +226,20 @@ void drm_gem_shmem_put_pages_locked(struct drm_gem_shmem_object *shmem) > } > EXPORT_SYMBOL_GPL(drm_gem_shmem_put_pages_locked); > > +static int drm_gem_shmem_get_pages(struct drm_gem_shmem_object *shmem) > +{ > + int ret; Just random drive-by comment: a might_lock annotation here might be good, or people could hit some really interesting bugs that are rather hard to reproduce ... -Sima > + > + if (refcount_inc_not_zero(&shmem->pages_use_count)) > + return 0; > + > + dma_resv_lock(shmem->base.resv, NULL); > + ret = drm_gem_shmem_get_pages_locked(shmem); > + dma_resv_unlock(shmem->base.resv); > + > + return ret; > +} > + > static int drm_gem_shmem_pin_locked(struct drm_gem_shmem_object *shmem) > { > int ret; > @@ -609,10 +623,7 @@ int drm_gem_shmem_mmap(struct drm_gem_shmem_object *shmem, struct vm_area_struct > return ret; > } > > - dma_resv_lock(shmem->base.resv, NULL); > - ret = drm_gem_shmem_get_pages_locked(shmem); > - dma_resv_unlock(shmem->base.resv); > - > + ret = drm_gem_shmem_get_pages(shmem); > if (ret) > return ret; > > -- > 2.43.0 > -- Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch