linux-kernel - [PATCH v15 02/23] drm/shmem-helper: Use flag for tracking page count bumped by get_pages

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Message-ID: <20230827175449.1766701-3-dmitry.osipenko@collabora.com>
Date:   Sun, 27 Aug 2023 20:54:28 +0300
From:   Dmitry Osipenko <dmitry.osipenko@...labora.com>
To:     David Airlie <airlied@...il.com>,
        Gerd Hoffmann <kraxel@...hat.com>,
        Gurchetan Singh <gurchetansingh@...omium.org>,
        Chia-I Wu <olvaffe@...il.com>, Daniel Vetter <daniel@...ll.ch>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        Christian König <christian.koenig@....com>,
        Qiang Yu <yuq825@...il.com>,
        Steven Price <steven.price@....com>,
        Boris Brezillon <boris.brezillon@...labora.com>,
        Emma Anholt <emma@...olt.net>, Melissa Wen <mwen@...lia.com>,
        Will Deacon <will@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Boqun Feng <boqun.feng@...il.com>,
        Mark Rutland <mark.rutland@....com>
Cc:     dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        kernel@...labora.com, virtualization@...ts.linux-foundation.org,
        intel-gfx@...ts.freedesktop.org
Subject: [PATCH v15 02/23] drm/shmem-helper: Use flag for tracking page count bumped by get_pages_sgt()

Use separate flag for tracking page count bumped by shmem->sgt to avoid
imbalanced page counter during of drm_gem_shmem_free() time. It's fragile
to assume that populated shmem->pages at a freeing time means that the
count was bumped by drm_gem_shmem_get_pages_sgt(), using a flag removes
the ambiguity.

Signed-off-by: Dmitry Osipenko <dmitry.osipenko@...labora.com>
---
 drivers/gpu/drm/drm_gem_shmem_helper.c | 3 ++-
 drivers/gpu/drm/lima/lima_gem.c        | 1 +
 include/drm/drm_gem_shmem_helper.h     | 7 +++++++
 3 files changed, 10 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/drm_gem_shmem_helper.c b/drivers/gpu/drm/drm_gem_shmem_helper.c
index 78d9cf2355a5..db20b9123891 100644
--- a/drivers/gpu/drm/drm_gem_shmem_helper.c
+++ b/drivers/gpu/drm/drm_gem_shmem_helper.c
@@ -152,7 +152,7 @@ void drm_gem_shmem_free(struct drm_gem_shmem_object *shmem)
 			sg_free_table(shmem->sgt);
 			kfree(shmem->sgt);
 		}
-		if (shmem->pages)
+		if (shmem->got_sgt)
 			drm_gem_shmem_put_pages(shmem);
 
 		drm_WARN_ON(obj->dev, shmem->pages_use_count);
@@ -687,6 +687,7 @@ static struct sg_table *drm_gem_shmem_get_pages_sgt_locked(struct drm_gem_shmem_
 	if (ret)
 		goto err_free_sgt;
 
+	shmem->got_sgt = true;
 	shmem->sgt = sgt;
 
 	return sgt;
diff --git a/drivers/gpu/drm/lima/lima_gem.c b/drivers/gpu/drm/lima/lima_gem.c
index 4f9736e5f929..28602302c281 100644
--- a/drivers/gpu/drm/lima/lima_gem.c
+++ b/drivers/gpu/drm/lima/lima_gem.c
@@ -89,6 +89,7 @@ int lima_heap_alloc(struct lima_bo *bo, struct lima_vm *vm)
 	}
 
 	*bo->base.sgt = sgt;
+	bo->base.got_sgt = true;
 
 	if (vm) {
 		ret = lima_vm_map_bo(vm, bo, old_size >> PAGE_SHIFT);
diff --git a/include/drm/drm_gem_shmem_helper.h b/include/drm/drm_gem_shmem_helper.h
index ec70a98a8fe1..f87124629bb5 100644
--- a/include/drm/drm_gem_shmem_helper.h
+++ b/include/drm/drm_gem_shmem_helper.h
@@ -73,6 +73,13 @@ struct drm_gem_shmem_object {
 	 */
 	unsigned int vmap_use_count;
 
+	/**
+	 * @got_sgt:
+	 *
+	 * True if SG table was retrieved using drm_gem_shmem_get_pages_sgt()
+	 */
+	bool got_sgt : 1;
+
 	/**
 	 * @imported_sgt:
 	 *
-- 
2.41.0