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Subject[058/127] drm/ttm: Clear the ghost cpu_writers flag on ttm_buffer_object_transfer.
2.6.32-stable review patch.  If anyone has any objections, please let us know.


From: Francisco Jerez <>

commit 0fbecd400dd0a82d465b3086f209681e8c54cb0f upstream.

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 <>
Signed-off-by: Greg Kroah-Hartman <>

drivers/gpu/drm/ttm/ttm_bo_util.c | 1 +
1 file changed, 1 insertion(+)

--- a/drivers/gpu/drm/ttm/ttm_bo_util.c
+++ b/drivers/gpu/drm/ttm/ttm_bo_util.c
@@ -330,6 +330,7 @@ static int ttm_buffer_object_transfer(st
fbo->vm_node = NULL;
+ atomic_set(&fbo->cpu_writers, 0);

fbo->sync_obj = driver->sync_obj_ref(bo->sync_obj);
if (fbo->mem.mm_node)

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