[PATCH] drm/ttm: fix two regressions since move_notify changes

[Thomas Hellstrom]

On 01/25/2012 06:34 AM, Ben Skeggs wrote:
> From: Ben Skeggs<bskeggs at redhat.com>
>
> Both changes in dc97b3409a790d2a21aac6e5cdb99558b5944119 cause serious
> regressions in the nouveau driver.
>
> move_notify() was originally able to presume that bo->mem is the old node,
> and new_mem is the new node.  The above commit moves the call to
> move_notify() to after move() has been done, which means that now, sometimes,
> new_mem isn't the new node at all, bo->mem is, and new_mem points at a
> stale, possibly-just-been-killed-by-move node.
>
> This is clearly not a good situation.  This patch reverts this change, and
> replaces it with a cleanup in the move() failure path instead.

While I have nothing against having move_notify() happening before the 
move, but
I still very much dislike  the failure path thing, since it puts a 
requirement on TTM to support
driver moves through move_notify(), which is done by Radeon.
I've kindly asked Jerome to change that, stating a number of reasons, 
but he refuses, and I'm
not prepared to let support for that mode of operation sneak in like this.


The second issue is that the call to move_notify() from cleanup_memtype_use()
causes the TTM ghost objects to get passed into the driver.  This is clearly
bad as the driver knows nothing about these "fake" TTM BOs, and ends up
accessing uninitialised memory.

I worked around this in nouveau's move_notify() hook by ensuring the BO
destructor was nouveau's.  I don't particularly like this solution, and
would rather TTM never pass the driver these objects.  However, I don't
clearly understand the reason why we're calling move_notify() here anyway
and am happy to work around the problem in nouveau instead of breaking the
behaviour expected by other drivers.


move_notify() here gives the driver a chance to unbind any GPU maps 
remaining on the BO
before it changes placement or is destroyed.
We've previously required the driver to support any type of BO in the 
driver hooks, I agree
with you that it would be desirable to make that go away.

Signed-off-by: Ben Skeggs<bskeggs at redhat.com>
Cc: Jerome Glisse<j.glisse at gmail.com>
---
  drivers/gpu/drm/nouveau/nouveau_bo.c |    4 ++++
  drivers/gpu/drm/ttm/ttm_bo.c         |   17 +++++++++++++----
  2 files changed, 17 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/nouveau/nouveau_bo.c b/drivers/gpu/drm/nouveau/nouveau_bo.c
index 724b41a..ec54364 100644
--- a/drivers/gpu/drm/nouveau/nouveau_bo.c
+++ b/drivers/gpu/drm/nouveau/nouveau_bo.c
@@ -812,6 +812,10 @@ nouveau_bo_move_ntfy(struct ttm_buffer_object *bo, struct ttm_mem_reg *new_mem)
  	struct nouveau_bo *nvbo = nouveau_bo(bo);
  	struct nouveau_vma *vma;

+	/* ttm can now (stupidly) pass the driver bos it didn't create... */
+	if (bo->destroy != nouveau_bo_del_ttm)
+		return;
+
  	list_for_each_entry(vma,&nvbo->vma_list, head) {
  		if (new_mem&&  new_mem->mem_type == TTM_PL_VRAM) {
  			nouveau_vm_map(vma, new_mem->mm_node);
diff --git a/drivers/gpu/drm/ttm/ttm_bo.c b/drivers/gpu/drm/ttm/ttm_bo.c
index 2f0eab6..7c3a57d 100644
--- a/drivers/gpu/drm/ttm/ttm_bo.c
+++ b/drivers/gpu/drm/ttm/ttm_bo.c
@@ -404,6 +404,9 @@ static int ttm_bo_handle_move_mem(struct ttm_buffer_object *bo,
  		}
  	}

+	if (bdev->driver->move_notify)
+		bdev->driver->move_notify(bo, mem);
+
  	if (!(old_man->flags&  TTM_MEMTYPE_FLAG_FIXED)&&
  	!(new_man->flags&  TTM_MEMTYPE_FLAG_FIXED))
  		ret = ttm_bo_move_ttm(bo, evict, no_wait_reserve, no_wait_gpu, mem);
@@ -413,11 +416,17 @@ static int ttm_bo_handle_move_mem(struct ttm_buffer_object *bo,
  	else
  		ret = ttm_bo_move_memcpy(bo, evict, no_wait_reserve, no_wait_gpu, mem);

-	if (ret)
-		goto out_err;
+	if (ret) {
+		if (bdev->driver->move_notify) {
+			struct ttm_mem_reg tmp_mem = *mem;
+			*mem = bo->mem;
+			bo->mem = tmp_mem;
+			bdev->driver->move_notify(bo, mem);
+			bo->mem = *mem;
+		}

-	if (bdev->driver->move_notify)
-		bdev->driver->move_notify(bo, mem);
+		goto out_err;
+	}

  moved:
  	if (bo->evicted) {