Re: [PATCH v10 06/11] drm/shmem-helper: Don't use vmap_use_count for dma-bufs

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Hi

Am 08.01.23 um 22:04 schrieb Dmitry Osipenko:
DMA-buf core has its own refcounting of vmaps, use it instead of drm-shmem
counting. This change prepares drm-shmem for addition of memory shrinker
support where drm-shmem will use a single dma-buf reservation lock for
all operations performed over dma-bufs.

Signed-off-by: Dmitry Osipenko <dmitry.osipenko@xxxxxxxxxxxxx>

Reviewed-by: Thomas Zimmermann <tzimmermann@xxxxxxx>

with my comments below considered.

---
  drivers/gpu/drm/drm_gem_shmem_helper.c | 35 +++++++++++++++-----------
  1 file changed, 20 insertions(+), 15 deletions(-)

diff --git a/drivers/gpu/drm/drm_gem_shmem_helper.c b/drivers/gpu/drm/drm_gem_shmem_helper.c
index 5006f7da7f2d..1392cbd3cc02 100644
--- a/drivers/gpu/drm/drm_gem_shmem_helper.c
+++ b/drivers/gpu/drm/drm_gem_shmem_helper.c
@@ -301,24 +301,22 @@ static int drm_gem_shmem_vmap_locked(struct drm_gem_shmem_object *shmem,
  	struct drm_gem_object *obj = &shmem->base;
  	int ret = 0;
- if (shmem->vmap_use_count++ > 0) {
-		iosys_map_set_vaddr(map, shmem->vaddr);
-		return 0;
-	}
-
  	if (obj->import_attach) {
  		ret = dma_buf_vmap(obj->import_attach->dmabuf, map);
  		if (!ret) {
  			if (drm_WARN_ON(obj->dev, map->is_iomem)) {

I'm sure that I added this line at some point. But I'm now wondering why we're testing this flag. Everything that uses the mapped buffer should by agnostic to is_iomem. IIRC the only reason for this test is is that we're setting shmem->vaddr to the returned map->vaddr. Now that the code is gone, we can also remove that whole branch.

  				dma_buf_vunmap(obj->import_attach->dmabuf, map);
-				ret = -EIO;
-				goto err_put_pages;
+				return -EIO;
  			}
-			shmem->vaddr = map->vaddr;
  		}
  	} else {
  		pgprot_t prot = PAGE_KERNEL;
+ if (shmem->vmap_use_count++ > 0) {
+			iosys_map_set_vaddr(map, shmem->vaddr);
+			return 0;
+		}
+
  		ret = drm_gem_shmem_get_pages(shmem);
  		if (ret)
  			goto err_zero_use;
@@ -384,15 +382,15 @@ static void drm_gem_shmem_vunmap_locked(struct drm_gem_shmem_object *shmem,
  {
  	struct drm_gem_object *obj = &shmem->base;
- if (drm_WARN_ON_ONCE(obj->dev, !shmem->vmap_use_count))
-		return;
-
-	if (--shmem->vmap_use_count > 0)
-		return;
-
  	if (obj->import_attach) {
  		dma_buf_vunmap(obj->import_attach->dmabuf, map);
  	} else {
+		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_put_pages(shmem);
  	}
@@ -660,7 +658,14 @@ void drm_gem_shmem_print_info(const struct drm_gem_shmem_object *shmem,
  			      struct drm_printer *p, unsigned int indent)
  {
  	drm_printf_indent(p, indent, "pages_use_count=%u\n", shmem->pages_use_count);
-	drm_printf_indent(p, indent, "vmap_use_count=%u\n", shmem->vmap_use_count);
+
+	if (shmem->base.import_attach)
+		drm_printf_indent(p, indent, "vmap_use_count=%u\n",
+				  shmem->base.dma_buf->vmapping_counter);

This is not vmap_use_count and the best solution is to add a print_info callback to dma_bufs. So Maybe simply ignore imported buffers here.

Best regards
Thomas

+	else
+		drm_printf_indent(p, indent, "vmap_use_count=%u\n",
+				  shmem->vmap_use_count);
+
  	drm_printf_indent(p, indent, "vaddr=%p\n", shmem->vaddr);
  }
  EXPORT_SYMBOL(drm_gem_shmem_print_info);

--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Maxfeldstr. 5, 90409 Nürnberg, Germany
(HRB 36809, AG Nürnberg)
Geschäftsführer: Ivo Totev

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