Re: [PATCH] drm/ttm: fix error handling in ttm_bo_handle_move_mem()

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Sending the first message didn't worked, so let's try again.

Am 16.06.21 um 08:30 schrieb Dan Carpenter:
There are three bugs here:
1) We need to call unpopulate() if ttm_tt_populate() succeeds.
2) The "new_man = ttm_manager_type(bdev, bo->mem.mem_type);" assignment
    was wrong and it was really assigning "new_mem = old_mem;".  There
    is no need for this assignment anyway as we already have the value
    for "new_mem".
3) The (!new_man->use_tt) condition is reversed.

Fixes: ba4e7d973dd0 ("drm: Add the TTM GPU memory manager subsystem.")
Signed-off-by: Dan Carpenter <dan.carpenter@xxxxxxxxxx>
---
This is from reading the code and I can't swear that I have understood
it correctly.  My nouveau driver is currently unusable and this patch
has not helped.  But hopefully if I fix enough bugs eventually it will
start to work.

Well NAK, the code previously looked quite well and you are breaking it now.

What's the problem with nouveau?

  drivers/gpu/drm/ttm/ttm_bo.c | 14 ++++++++------
  1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/drivers/gpu/drm/ttm/ttm_bo.c b/drivers/gpu/drm/ttm/ttm_bo.c
index ebcffe794adb..72dde093f754 100644
--- a/drivers/gpu/drm/ttm/ttm_bo.c
+++ b/drivers/gpu/drm/ttm/ttm_bo.c
@@ -180,12 +180,12 @@ static int ttm_bo_handle_move_mem(struct ttm_buffer_object *bo,
  		 */
  		ret = ttm_tt_create(bo, old_man->use_tt);
  		if (ret)
-			goto out_err;
+			return ret;
if (mem->mem_type != TTM_PL_SYSTEM) {
  			ret = ttm_tt_populate(bo->bdev, bo->ttm, ctx);
  			if (ret)
-				goto out_err;
+				goto err_destroy;
  		}
  	}
@@ -193,15 +193,17 @@ static int ttm_bo_handle_move_mem(struct ttm_buffer_object *bo,
  	if (ret) {
  		if (ret == -EMULTIHOP)
  			return ret;
-		goto out_err;
+		goto err_unpopulate;
  	}
ctx->bytes_moved += bo->base.size;
  	return 0;
-out_err:
-	new_man = ttm_manager_type(bdev, bo->mem.mem_type);

This here switches new and old manager. E.g. the new_man is now pointing to the existing resource manager.

-	if (!new_man->use_tt)

So we should destroy the TT object only if the old manager is not using one.

+err_unpopulate:
+	if (new_man->use_tt)
+		ttm_tt_unpopulate(bo->bdev, bo->ttm);

Unpopulate is not necessary, destroying is sufficient.

Christian.

+err_destroy:
+	if (new_man->use_tt)
  		ttm_bo_tt_destroy(bo);
return ret;




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