A few callers need to serialise the destruction of their drm_mm_node and ensure it is removed from the drm_mm before freeing. However, to be completely sure that any access from another thread is complete before we free the struct, we require the RELEASE semantics of clear_bit_unlock().
This allows the conditional locking such as
Thread A Thread B mutex_lock(mm_lock); if (drm_mm_node_allocated(node)) { drm_mm_node_remove(node); mutex_lock(mm_lock); mutex_unlock(mm_lock); drm_mm_node_remove(node); mutex_unlock(mm_lock); } kfree(node);
to serialise correctly without any lingering accesses from A to the freed node. Allocation / insertion of the node is assumed never to race with removal or eviction scanning.
Signed-off-by: Chris Wilson chris@chris-wilson.co.uk --- drivers/gpu/drm/drm_mm.c | 11 ++++++----- 1 file changed, 6 insertions(+), 5 deletions(-)
diff --git a/drivers/gpu/drm/drm_mm.c b/drivers/gpu/drm/drm_mm.c index a9cab5e53731..2a6e34663146 100644 --- a/drivers/gpu/drm/drm_mm.c +++ b/drivers/gpu/drm/drm_mm.c @@ -424,9 +424,9 @@ int drm_mm_reserve_node(struct drm_mm *mm, struct drm_mm_node *node)
node->mm = mm;
+ __set_bit(DRM_MM_NODE_ALLOCATED_BIT, &node->flags); list_add(&node->node_list, &hole->node_list); drm_mm_interval_tree_add_node(hole, node); - __set_bit(DRM_MM_NODE_ALLOCATED_BIT, &node->flags); node->hole_size = 0;
rm_hole(hole); @@ -543,9 +543,9 @@ int drm_mm_insert_node_in_range(struct drm_mm * const mm, node->color = color; node->hole_size = 0;
+ __set_bit(DRM_MM_NODE_ALLOCATED_BIT, &node->flags); list_add(&node->node_list, &hole->node_list); drm_mm_interval_tree_add_node(hole, node); - __set_bit(DRM_MM_NODE_ALLOCATED_BIT, &node->flags);
rm_hole(hole); if (adj_start > hole_start) @@ -589,11 +589,12 @@ void drm_mm_remove_node(struct drm_mm_node *node)
drm_mm_interval_tree_remove(node, &mm->interval_tree); list_del(&node->node_list); - __clear_bit(DRM_MM_NODE_ALLOCATED_BIT, &node->flags);
if (drm_mm_hole_follows(prev_node)) rm_hole(prev_node); add_hole(prev_node); + + clear_bit_unlock(DRM_MM_NODE_ALLOCATED_BIT, &node->flags); } EXPORT_SYMBOL(drm_mm_remove_node);
@@ -614,6 +615,7 @@ void drm_mm_replace_node(struct drm_mm_node *old, struct drm_mm_node *new)
*new = *old;
+ __set_bit(DRM_MM_NODE_ALLOCATED_BIT, &new->flags); list_replace(&old->node_list, &new->node_list); rb_replace_node_cached(&old->rb, &new->rb, &mm->interval_tree);
@@ -627,8 +629,7 @@ void drm_mm_replace_node(struct drm_mm_node *old, struct drm_mm_node *new) &mm->holes_addr); }
- __clear_bit(DRM_MM_NODE_ALLOCATED_BIT, &old->flags); - __set_bit(DRM_MM_NODE_ALLOCATED_BIT, &new->flags); + clear_bit_unlock(DRM_MM_NODE_ALLOCATED_BIT, &old->flags); } EXPORT_SYMBOL(drm_mm_replace_node);