Re: [PATCH] drm/amdgpu: Add explicit NULL check for bo in amdgpu_vm_bo_update()

[Dan Carpenter <dan.carpenter@linaro.org>]

On Thu, Mar 12, 2026 at 02:39:34PM +0000, Tvrtko Ursulin wrote:
> 
> On 12/03/2026 14:13, Srinivasan Shanmugam wrote:
> > amdgpu_vm_bo_update() allows bo_va->base.bo to be NULL in some paths,
> > such as PRT-only updates.
> > 
> > Although amdgpu_vm_is_bo_always_valid() already returns false for a NULL
> > BO, Smatch still warns that bo may be NULL before it is dereferenced
> > later in the block.
> > 
> > Add an explicit `bo &&` check before calling
> > amdgpu_vm_is_bo_always_valid() to make the non-NULL condition clear and
> > fixes the below smatch error
> > 
> > drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c:1353 amdgpu_vm_bo_update() error: we previously assumed 'bo' could be null (see line 1292)
> > 
> > Fixes: 26e20235ce00 ("drm/amdgpu: Add amdgpu_bo_is_vm_bo helper")
> > Cc: Dan Carpenter <dan.carpenter@linaro.org>
> > Cc: Tvrtko Ursulin <tvrtko.ursulin@igalia.com>
> > Cc: Christian König <christian.koenig@amd.com>
> > Cc: Alex Deucher <alexander.deucher@amd.com>
> > Signed-off-by: Srinivasan Shanmugam <srinivasan.shanmugam@amd.com>
> > ---
> >   drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c | 2 +-
> >   1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c
> > index b89013a6aa0b..0d26346178d4 100644
> > --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c
> > +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c
> > @@ -1349,7 +1349,7 @@ int amdgpu_vm_bo_update(struct amdgpu_device *adev, struct amdgpu_bo_va *bo_va,
> >   	 * the evicted list so that it gets validated again on the
> >   	 * next command submission.
> >   	 */
> > -	if (amdgpu_vm_is_bo_always_valid(vm, bo)) {
> > +	if (bo && amdgpu_vm_is_bo_always_valid(vm, bo)) {
> 
> That would be unfortunate:
> 
> bool amdgpu_vm_is_bo_always_valid(struct amdgpu_vm *vm, struct amdgpu_bo
> *bo)
> {
> 	return bo && bo->tbo.base.resv == vm->root.bo->tbo.base.resv;
> }
> 
> Maybe Dan can make smatch smarter? :) Because I don't think papering
> randomly at a single call site is great. It is even in the same compilation
> unit. Hmm does the order matter to smatch? Should we maybe move
> amdgpu_vm_is_bo_always_valid() to be earlier in the file?

I'm glad moving the function earlier fixed it.  :)  The function ends
up getting inlined.  This warning should only show up if you don't have
the cross function database built.

https://staticthinking.wordpress.com/2023/05/02/the-cross-function-db/

regards,
dan carpenter