path: root/drivers/gpu/drm
diff options
authorDaniel Vetter <>2013-08-15 00:02:32 +0200
committerChanho Park <>2014-11-21 19:12:24 +0900
commit44626077c9f062429b9ca345db1a4ff937d38542 (patch)
treefc0730dff3860617bf78862842a9f5ee57148146 /drivers/gpu/drm
parent409dab234bc53888679581a0df968638f3ff90ba (diff)
drm/prime: remove cargo-cult locking from map_sg helper
I've checked both implementations (radeon/nouveau) and they both grab the page array from ttm simply by dereferencing it and then wrapping it up with drm_prime_pages_to_sg in the callback and map it with dma_map_sg (in the helper). Only the grabbing of the underlying page array is anything we need to be concerned about, and either those pages are pinned independently, or we're screwed no matter what. And indeed, nouveau/radeon pin the backing storage in their attach/detach functions. Since I've created this patch cma prime support for dma_buf was added. drm_gem_cma_prime_get_sg_table only calls kzalloc and the creates&maps the sg table with dma_get_sgtable. It doesn't touch any gem object state otherwise. So the cma helpers also look safe. The only thing we might claim it does is prevent concurrent mapping of dma_buf attachments. But a) that's not allowed and b) the current code is racy already since it checks whether the sg mapping exists _before_ grabbing the lock. So the dev->struct_mutex locking here does absolutely nothing useful, but only distracts. Remove it. This should also help Maarten's work to eventually pin the backing storage more dynamically by preventing locking inversions around dev->struct_mutex. v2: Add analysis for recently added cma helper prime code. Cc: Laurent Pinchart <> Cc: Maarten Lankhorst <> Acked-by: Laurent Pinchart <> Acked-by: Maarten Lankhorst <> Signed-off-by: Daniel Vetter <> Signed-off-by: Dave Airlie <>
Diffstat (limited to 'drivers/gpu/drm')
1 files changed, 0 insertions, 3 deletions
diff --git a/drivers/gpu/drm/drm_prime.c b/drivers/gpu/drm/drm_prime.c
index 068a8f2b1da..d39fe52560d 100644
--- a/drivers/gpu/drm/drm_prime.c
+++ b/drivers/gpu/drm/drm_prime.c
@@ -167,8 +167,6 @@ static struct sg_table *drm_gem_map_dma_buf(struct dma_buf_attachment *attach,
if (WARN_ON(prime_attach->dir != DMA_NONE))
return ERR_PTR(-EBUSY);
- mutex_lock(&obj->dev->struct_mutex);
sgt = obj->dev->driver->gem_prime_get_sg_table(obj);
if (!IS_ERR(sgt)) {
@@ -182,7 +180,6 @@ static struct sg_table *drm_gem_map_dma_buf(struct dma_buf_attachment *attach,
- mutex_unlock(&obj->dev->struct_mutex);
return sgt;