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From:   Dmitry Osipenko <dmitry.osipenko@collabora.com>
To:     David Airlie <airlied@gmail.com>,
        Gerd Hoffmann <kraxel@redhat.com>,
        Gurchetan Singh <gurchetansingh@chromium.org>,
        Chia-I Wu <olvaffe@gmail.com>, Daniel Vetter <daniel@ffwll.ch>,
        Maarten Lankhorst <maarten.lankhorst@linux.intel.com>,
        Maxime Ripard <mripard@kernel.org>,
        Thomas Zimmermann <tzimmermann@suse.de>,
        =?UTF-8?q?Christian=20K=C3=B6nig?= <christian.koenig@amd.com>,
        Qiang Yu <yuq825@gmail.com>,
        Steven Price <steven.price@arm.com>,
        Boris Brezillon <boris.brezillon@collabora.com>,
        Emma Anholt <emma@anholt.net>, Melissa Wen <mwen@igalia.com>
Cc:     dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org,
        kernel@collabora.com, virtualization@lists.linux-foundation.org
Subject: [PATCH v18 08/26] drm/shmem-helper: Add and use lockless drm_gem_shmem_get_pages()
Date:   Mon, 30 Oct 2023 02:01:47 +0300
Message-ID: <20231029230205.93277-9-dmitry.osipenko@collabora.com>
In-Reply-To: <20231029230205.93277-1-dmitry.osipenko@collabora.com>
References: <20231029230205.93277-1-dmitry.osipenko@collabora.com>
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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.

Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>
Suggested-by: Boris Brezillon <boris.brezillon@collabora.com>
Signed-off-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>
---
 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 6e02643ed87e..41b749bedb11 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;
+
+	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;
 
-- 
2.41.0