Re: [PATCH] drm/amdkfd: fix kgd_mem memory leak when importing dmabuf

[Lang Yu <Lang.Yu@amd.com>]

On 07/26/ , Felix Kuehling wrote:
> Am 2022-07-26 um 07:15 schrieb Lang Yu:
> > The kgd_mem memory allocated in amdgpu_amdkfd_gpuvm_import_dmabuf()
> > is not freed properly.
> > 
> > Explicitly free it in amdgpu_amdkfd_gpuvm_free_memory_of_gpu()
> > under condition "mem->bo->kfd_bo != mem".
> > 
> > Suggested-by: Felix Kuehling <Felix.Kuehling@amd.com>
> > Signed-off-by: Lang Yu <Lang.Yu@amd.com>
> 
> Some suggestions inline to make the code more readable. Other than that, the
> patch is
> 
> Reviewed-by: Felix Kuehling <Felix.Kuehling@amd.com>
> 
> 
> > ---
> >   drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_gpuvm.c | 8 ++++++++
> >   1 file changed, 8 insertions(+)
> > 
> > diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_gpuvm.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_gpuvm.c
> > index 6bba6961eee7..086bed40cf34 100644
> > --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_gpuvm.c
> > +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_gpuvm.c
> > @@ -1803,6 +1803,7 @@ int amdgpu_amdkfd_gpuvm_free_memory_of_gpu(
> >   		uint64_t *size)
> >   {
> >   	struct amdkfd_process_info *process_info = mem->process_info;
> > +	struct kgd_mem *tmp_mem = mem->bo->kfd_bo;
> 
> Right, you need this because using mem after drm_gem_object_put would be a
> potential use-after-free. Instead of saving this pointer with some obscure
> variable name, you could just save a bool with a more meaningful name. E.g.:
> 
> 	bool use_release_notifier = (mem->bo->kfd_bo == mem);
> 
> This way you have the entire condition in one place, and the variable name
> explains the meaning.

Got it. Thanks!

Regards,
Lang

> 
> >   	unsigned long bo_size = mem->bo->tbo.base.size;
> >   	struct kfd_mem_attachment *entry, *tmp;
> >   	struct bo_vm_reservation_context ctx;
> > @@ -1895,6 +1896,13 @@ int amdgpu_amdkfd_gpuvm_free_memory_of_gpu(
> >   	 */
> >   	drm_gem_object_put(&mem->bo->tbo.base);
> > +	/*
> > +	 * For kgd_mem allocated in amdgpu_amdkfd_gpuvm_import_dmabuf(),
> > +	 * explicitly free it here.
> > +	 */
> > +	if (mem != tmp_mem)
> 
> 	if (!use_release_notifier)
> 		kfree(mem);
> 
> Regards,
>   Felix
> 
> 
> > +		kfree(mem);
> > +
> >   	return ret;
> >   }