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From 0fbecd400dd0a82d465b3086f209681e8c54cb0f Mon Sep 17 00:00:00 2001
From: Francisco Jerez <>
Date: Tue, 21 Sep 2010 02:15:15 +0200
Subject: [PATCH] drm/ttm: Clear the ghost cpu_writers flag on ttm_buffer_object_transfer.

It makes sense for a BO to move after a process has requested
exclusive RW access on it (e.g. because the BO used to be located in
unmappable VRAM and we intercepted the CPU access from the fault

If we let the ghost object inherit cpu_writers from the original
object, ttm_bo_release_list() will raise a kernel BUG when the ghost
object is destroyed. This can be reproduced with the nouveau driver on

Reported-by: Marcin Slusarz <>
Reviewed-by: Jerome Glisse <>
Tested-by: Marcin Slusarz <>
Signed-off-by: Francisco Jerez <>
Signed-off-by: Dave Airlie <>
 drivers/gpu/drm/ttm/ttm_bo_util.c |    1 +
 1 files changed, 1 insertions(+), 0 deletions(-)

diff --git a/drivers/gpu/drm/ttm/ttm_bo_util.c b/drivers/gpu/drm/ttm/ttm_bo_util.c
index 7cffb3e..3451a82 100644
--- a/drivers/gpu/drm/ttm/ttm_bo_util.c
+++ b/drivers/gpu/drm/ttm/ttm_bo_util.c
@@ -351,6 +351,7 @@ static int ttm_buffer_object_transfer(struct ttm_buffer_object *bo,
 	fbo->vm_node = NULL;
+	atomic_set(&fbo->cpu_writers, 0);
 	fbo->sync_obj = driver->sync_obj_ref(bo->sync_obj);