Re: [PATCH] drm/amdgpu: Remove hidden double memset from amdgpu_vm_pt_clear()

[Tvrtko Ursulin]

On 13/08/2024 15:08, Tvrtko Ursulin wrote:
From: Tvrtko Ursulin <tvrtko.ursu...@igalia.com>

When CONFIG_INIT_STACK_ALL_ZERO is set and so -ftrivial-auto-var-init=zero
compiler option active, compiler fails to notice that later in
amdgpu_vm_pt_clear() there  is a second memset to clear the same on stack
struct amdgpu_vm_update_params.

If we replace this memset with an explicit automatic variable initializer,
compiler can then see it and avoid clearing this struct twice.

Signed-off-by: Tvrtko Ursulin <tvrtko.ursu...@igalia.com>
---
This is perhaps a bit questionable, regardless of how annoying it is to
know there is this double memset.
---
  drivers/gpu/drm/amd/amdgpu/amdgpu_vm_pt.c | 3 +--
  1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm_pt.c 
b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm_pt.c
index e39d6e7643bf..ecdc8fffe941 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm_pt.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm_pt.c
@@ -361,7 +361,7 @@ int amdgpu_vm_pt_clear(struct amdgpu_device *adev, struct 
amdgpu_vm *vm,
  {
        unsigned int level = adev->vm_manager.root_level;
        struct ttm_operation_ctx ctx = { true, false };
-       struct amdgpu_vm_update_params params;
+       struct amdgpu_vm_update_params params = { };
        struct amdgpu_bo *ancestor = &vmbo->bo;
        unsigned int entries;
        struct amdgpu_bo *bo = &vmbo->bo;
@@ -398,7 +398,6 @@ int amdgpu_vm_pt_clear(struct amdgpu_device *adev, struct 
amdgpu_vm *vm,
        if (r)
                goto exit;
  
-	memset(&params, 0, sizeof(params));
        params.adev = adev;
        params.vm = vm;
        params.immediate = immediate;

Or even move all above three into the automatic initializer since all 
are the function input arguments.

Regards,

Tvrtko