drm: mm always protect change to unused_nodes with unused_lock spinlock

unused_nodes modification needs to be protected by unused_lock spinlock.
Here is an example of an usage where there is no such protection without
this patch.

  Process 1: 1-drm_mm_pre_get(this function modify unused_nodes list)
             2-spin_lock(spinlock protecting mm struct)
             3-drm_mm_put_block(this function might modify unused_nodes
               list but doesn't protect modification with unused_lock)
             4-spin_unlock(spinlock protecting mm struct)
  Process2:  1-drm_mm_pre_get(this function modify unused_nodes list)
At this point Process1 & Process2 might both be doing modification to
unused_nodes list. This patch add unused_lock protection into
drm_mm_put_block to avoid such issue.

Signed-off-by: Jerome Glisse <jglisse@redhat.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>

1 files changed, 9 insertions, 0 deletions

diff --git a/drivers/gpu/drm/drm_mm.c b/drivers/gpu/drm/drm_mm.c
index c861d80fd779..97dc5a4f0de4 100644
--- a/drivers/gpu/drm/drm_mm.c
+++ b/drivers/gpu/drm/drm_mm.c
@@ -103,6 +103,11 @@ static struct drm_mm_node *drm_mm_kmalloc(struct drm_mm *mm, int atomic)
         return child;
 }
 
+/* drm_mm_pre_get() - pre allocate drm_mm_node structure
+ * drm_mm:      memory manager struct we are pre-allocating for
+ *
+ * Returns 0 on success or -ENOMEM if allocation fails.
+ */
 int drm_mm_pre_get(struct drm_mm *mm)
 {
         struct drm_mm_node *node;
@@ -253,12 +258,14 @@ void drm_mm_put_block(struct drm_mm_node *cur)
                                 prev_node->size += next_node->size;
                                 list_del(&next_node->ml_entry);
                                 list_del(&next_node->fl_entry);
+                                spin_lock(&mm->unused_lock);
                                 if (mm->num_unused < MM_UNUSED_TARGET) {
                                         list_add(&next_node->fl_entry,
                                                  &mm->unused_nodes);
                                         ++mm->num_unused;
                                 } else
                                         kfree(next_node);
+                                spin_unlock(&mm->unused_lock);
                         } else {
                                 next_node->size += cur->size;
                                 next_node->start = cur->start;
@@ -271,11 +278,13 @@ void drm_mm_put_block(struct drm_mm_node *cur)
                 list_add(&cur->fl_entry, &mm->fl_entry);
         } else {
                 list_del(&cur->ml_entry);
+                spin_lock(&mm->unused_lock);
                 if (mm->num_unused < MM_UNUSED_TARGET) {
                         list_add(&cur->fl_entry, &mm->unused_nodes);
                         ++mm->num_unused;
                 } else
                         kfree(cur);
+                spin_unlock(&mm->unused_lock);
         }
 }