linux-kernel - [PATCH v16 14/20] drm/shmem-helper: Use refcount_t for vmap_use

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Message-ID: <20230903170736.513347-15-dmitry.osipenko@collabora.com>
Date:   Sun,  3 Sep 2023 20:07:30 +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>
Cc:     dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        kernel@...labora.com, virtualization@...ts.linux-foundation.org
Subject: [PATCH v16 14/20] drm/shmem-helper: Use refcount_t for vmap_use_count

Use refcount_t helper for vmap_use_count to make refcounting consistent
with pages_use_count and pages_pin_count that use refcount_t. This will
allow to optimize unlocked vmappings by skipping reservation locking if
refcnt > 1 and also makes vmapping to benefit from the refcount_t's
overflow checks.

Suggested-by: Boris Brezillon <boris.brezillon@...labora.com>
Signed-off-by: Dmitry Osipenko <dmitry.osipenko@...labora.com>
---
 drivers/gpu/drm/drm_gem_shmem_helper.c | 28 +++++++++++---------------
 include/drm/drm_gem_shmem_helper.h     |  2 +-
 2 files changed, 13 insertions(+), 17 deletions(-)

diff --git a/drivers/gpu/drm/drm_gem_shmem_helper.c b/drivers/gpu/drm/drm_gem_shmem_helper.c
index 899f655a65bb..4633a418faba 100644
--- a/drivers/gpu/drm/drm_gem_shmem_helper.c
+++ b/drivers/gpu/drm/drm_gem_shmem_helper.c
@@ -144,7 +144,7 @@ void drm_gem_shmem_free(struct drm_gem_shmem_object *shmem)
 	} else if (!shmem->imported_sgt) {
 		dma_resv_lock(shmem->base.resv, NULL);
 
-		drm_WARN_ON(obj->dev, shmem->vmap_use_count);
+		drm_WARN_ON(obj->dev, refcount_read(&shmem->vmap_use_count));
 
 		if (shmem->sgt) {
 			dma_unmap_sgtable(obj->dev->dev, shmem->sgt,
@@ -345,23 +345,25 @@ int drm_gem_shmem_vmap_locked(struct drm_gem_shmem_object *shmem,
 
 		dma_resv_assert_held(shmem->base.resv);
 
-		if (shmem->vmap_use_count++ > 0) {
+		if (refcount_inc_not_zero(&shmem->vmap_use_count)) {
 			iosys_map_set_vaddr(map, shmem->vaddr);
 			return 0;
 		}
 
 		ret = drm_gem_shmem_pin_locked(shmem);
 		if (ret)
-			goto err_zero_use;
+			return ret;
 
 		if (shmem->map_wc)
 			prot = pgprot_writecombine(prot);
 		shmem->vaddr = vmap(shmem->pages, obj->size >> PAGE_SHIFT,
 				    VM_MAP, prot);
-		if (!shmem->vaddr)
+		if (!shmem->vaddr) {
 			ret = -ENOMEM;
-		else
+		} else {
 			iosys_map_set_vaddr(map, shmem->vaddr);
+			refcount_set(&shmem->vmap_use_count, 1);
+		}
 	}
 
 	if (ret) {
@@ -374,8 +376,6 @@ int drm_gem_shmem_vmap_locked(struct drm_gem_shmem_object *shmem,
 err_put_pages:
 	if (!obj->import_attach)
 		drm_gem_shmem_unpin_locked(shmem);
-err_zero_use:
-	shmem->vmap_use_count = 0;
 
 	return ret;
 }
@@ -403,14 +403,10 @@ void drm_gem_shmem_vunmap_locked(struct drm_gem_shmem_object *shmem,
 	} else {
 		dma_resv_assert_held(shmem->base.resv);
 
-		if (drm_WARN_ON_ONCE(obj->dev, !shmem->vmap_use_count))
-			return;
-
-		if (--shmem->vmap_use_count > 0)
-			return;
-
-		vunmap(shmem->vaddr);
-		drm_gem_shmem_unpin_locked(shmem);
+		if (refcount_dec_and_test(&shmem->vmap_use_count)) {
+			vunmap(shmem->vaddr);
+			drm_gem_shmem_unpin_locked(shmem);
+		}
 	}
 
 	shmem->vaddr = NULL;
@@ -656,7 +652,7 @@ void drm_gem_shmem_print_info(const struct drm_gem_shmem_object *shmem,
 
 	drm_printf_indent(p, indent, "pages_pin_count=%u\n", refcount_read(&shmem->pages_pin_count));
 	drm_printf_indent(p, indent, "pages_use_count=%u\n", refcount_read(&shmem->pages_use_count));
-	drm_printf_indent(p, indent, "vmap_use_count=%u\n", shmem->vmap_use_count);
+	drm_printf_indent(p, indent, "vmap_use_count=%u\n", refcount_read(&shmem->vmap_use_count));
 	drm_printf_indent(p, indent, "vaddr=%p\n", shmem->vaddr);
 }
 EXPORT_SYMBOL_GPL(drm_gem_shmem_print_info);
diff --git a/include/drm/drm_gem_shmem_helper.h b/include/drm/drm_gem_shmem_helper.h
index 396958a98c34..63e91e8f2d5c 100644
--- a/include/drm/drm_gem_shmem_helper.h
+++ b/include/drm/drm_gem_shmem_helper.h
@@ -81,7 +81,7 @@ struct drm_gem_shmem_object {
 	 * Reference count on the virtual address.
 	 * The address are un-mapped when the count reaches zero.
 	 */
-	unsigned int vmap_use_count;
+	refcount_t vmap_use_count;
 
 	/**
 	 * @got_pages_sgt:
-- 
2.41.0