drm/vmwgfx: Fix a destoy-while-held mutex problem.

When validating legacy surfaces, the backup bo might be destroyed at
surface validate time. However, the kms resource validation code may have
the bo reserved, so we will destroy a locked mutex. While there shouldn't
be any other users of that mutex when it is destroyed, it causes a lock
leak and thus throws a lockdep error.

Fix this by having the kms resource validation code hold a reference to
the bo while we have it reserved. We do this by introducing a validation
context which might come in handy when the kms code is extended to validate
multiple resources or buffers.

Cc: <stable@vger.kernel.org>
Signed-off-by: Thomas Hellstrom <thellstrom@vmware.com>
Reviewed-by: Brian Paul <brianp@vmware.com>
Reviewed-by: Sinclair Yeh <syeh@vmware.com>

1 files changed, 19 insertions, 9 deletions

diff --git a/drivers/gpu/drm/vmwgfx/vmwgfx_kms.c b/drivers/gpu/drm/vmwgfx/vmwgfx_kms.c
index b3d62aa01a9b..3c824fd7cbf3 100644
--- a/drivers/gpu/drm/vmwgfx/vmwgfx_kms.c
+++ b/drivers/gpu/drm/vmwgfx/vmwgfx_kms.c
@@ -31,7 +31,6 @@
 #include <drm/drm_atomic_helper.h>
 #include <drm/drm_rect.h>
 
-
 /* Might need a hrtimer here? */
 #define VMWGFX_PRESENT_RATE ((HZ / 60 > 0) ? HZ / 60 : 1)
 
@@ -2517,9 +2516,12 @@ void vmw_kms_helper_buffer_finish(struct vmw_private *dev_priv,
  * Helper to be used if an error forces the caller to undo the actions of
  * vmw_kms_helper_resource_prepare.
  */
-void vmw_kms_helper_resource_revert(struct vmw_resource *res)
+void vmw_kms_helper_resource_revert(struct vmw_validation_ctx *ctx)
 {
-	vmw_kms_helper_buffer_revert(res->backup);
+	struct vmw_resource *res = ctx->res;
+
+	vmw_kms_helper_buffer_revert(ctx->buf);
+	vmw_dmabuf_unreference(&ctx->buf);
 	vmw_resource_unreserve(res, false, NULL, 0);
 	mutex_unlock(&res->dev_priv->cmdbuf_mutex);
 }
@@ -2536,10 +2538,14 @@ void vmw_kms_helper_resource_revert(struct vmw_resource *res)
  * interrupted by a signal.
  */
 int vmw_kms_helper_resource_prepare(struct vmw_resource *res,
-				    bool interruptible)
+				    bool interruptible,
+				    struct vmw_validation_ctx *ctx)
 {
 	int ret = 0;
 
+	ctx->buf = NULL;
+	ctx->res = res;
+
 	if (interruptible)
 		ret = mutex_lock_interruptible(&res->dev_priv->cmdbuf_mutex);
 	else
@@ -2558,6 +2564,8 @@ int vmw_kms_helper_resource_prepare(struct vmw_resource *res,
 						    res->dev_priv->has_mob);
 		if (ret)
 			goto out_unreserve;
+
+		ctx->buf = vmw_dmabuf_reference(res->backup);
 	}
 	ret = vmw_resource_validate(res);
 	if (ret)
@@ -2565,7 +2573,7 @@ int vmw_kms_helper_resource_prepare(struct vmw_resource *res,
 	return 0;
 
 out_revert:
-	vmw_kms_helper_buffer_revert(res->backup);
+	vmw_kms_helper_buffer_revert(ctx->buf);
 out_unreserve:
 	vmw_resource_unreserve(res, false, NULL, 0);
 out_unlock:
@@ -2581,11 +2589,13 @@ out_unlock:
  * @out_fence: Optional pointer to a fence pointer. If non-NULL, a
  * ref-counted fence pointer is returned here.
  */
-void vmw_kms_helper_resource_finish(struct vmw_resource *res,
-			     struct vmw_fence_obj **out_fence)
+void vmw_kms_helper_resource_finish(struct vmw_validation_ctx *ctx,
+				    struct vmw_fence_obj **out_fence)
 {
-	if (res->backup || out_fence)
-		vmw_kms_helper_buffer_finish(res->dev_priv, NULL, res->backup,
+	struct vmw_resource *res = ctx->res;
+
+	if (ctx->buf || out_fence)
+		vmw_kms_helper_buffer_finish(res->dev_priv, NULL, ctx->buf,
 					     out_fence, NULL);
 
 	vmw_resource_unreserve(res, false, NULL, 0);