drm/nouveau: try to protect nbo->pin_refcount

... by moving the bo_pin/bo_unpin manipulation of the pin_refcount
under the protection of the ttm reservation lock. pin/unpin seems
to get called from all over the place, so atm this is completely racy.

After this patch there are only a few places in cleanup functions
left which access ->pin_refcount without locking. But I'm hoping that
those are safe and some other code invariant guarantees that this
won't blow up.

In any case, I only need to fix up pin/unpin to make ->pageflip work
safely, so let's keep it at that.

Add a comment to the header to explain the new locking rule.

Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

2 files changed, 13 insertions, 11 deletions

diff --git a/drivers/gpu/drm/nouveau/nouveau_bo.c b/drivers/gpu/drm/nouveau/nouveau_bo.c
index 69d7b1d0b9d6..64d6e3047dee 100644
--- a/drivers/gpu/drm/nouveau/nouveau_bo.c
+++ b/drivers/gpu/drm/nouveau/nouveau_bo.c
@@ -300,17 +300,18 @@ nouveau_bo_pin(struct nouveau_bo *nvbo, uint32_t memtype)
         struct ttm_buffer_object *bo = &nvbo->bo;
         int ret;
 
+        ret = ttm_bo_reserve(bo, false, false, false, 0);
+        if (ret)
+                goto out;
+
         if (nvbo->pin_refcnt && !(memtype & (1 << bo->mem.mem_type))) {
                 NV_ERROR(drm, "bo %p pinned elsewhere: 0x%08x vs 0x%08x\n", bo,
                          1 << bo->mem.mem_type, memtype);
-                return -EINVAL;
+                ret = -EINVAL;
+                goto out;
         }
 
         if (nvbo->pin_refcnt++)
-                return 0;
-
-        ret = ttm_bo_reserve(bo, false, false, false, 0);
-        if (ret)
                 goto out;
 
         nouveau_bo_placement_set(nvbo, memtype, 0);
@@ -328,10 +329,8 @@ nouveau_bo_pin(struct nouveau_bo *nvbo, uint32_t memtype)
                         break;
                 }
         }
-        ttm_bo_unreserve(bo);
 out:
-        if (unlikely(ret))
-                nvbo->pin_refcnt--;
+        ttm_bo_unreserve(bo);
         return ret;
 }
 
@@ -342,13 +341,13 @@ nouveau_bo_unpin(struct nouveau_bo *nvbo)
         struct ttm_buffer_object *bo = &nvbo->bo;
         int ret;
 
-        if (--nvbo->pin_refcnt)
-                return 0;
-
         ret = ttm_bo_reserve(bo, false, false, false, 0);
         if (ret)
                 return ret;
 
+        if (--nvbo->pin_refcnt)
+                goto out;
+
         nouveau_bo_placement_set(nvbo, bo->mem.placement, 0);
 
         ret = nouveau_bo_validate(nvbo, false, false);
@@ -365,6 +364,7 @@ nouveau_bo_unpin(struct nouveau_bo *nvbo)
                 }
         }
 
+out:
         ttm_bo_unreserve(bo);
         return ret;
 }
diff --git a/drivers/gpu/drm/nouveau/nouveau_bo.h b/drivers/gpu/drm/nouveau/nouveau_bo.h
index 25ca37989d2c..81d00fe03b56 100644
--- a/drivers/gpu/drm/nouveau/nouveau_bo.h
+++ b/drivers/gpu/drm/nouveau/nouveau_bo.h
@@ -28,6 +28,8 @@ struct nouveau_bo {
         struct nouveau_drm_tile *tile;
 
         struct drm_gem_object *gem;
+
+        /* protect by the ttm reservation lock */
         int pin_refcnt;
 
         struct ttm_bo_kmap_obj dma_buf_vmap;