Re: [PATCH v2] nouveau/dmem: handle kcalloc() allocation failure

[Danilo Krummrich <dakr@redhat.com>]

Hi Duoming,

thanks for sending a V2.

On 3/5/24 15:39, Duoming Zhou wrote:
> The kcalloc() in nouveau_dmem_evict_chunk() will return null if
> the physical memory has run out. As a result, if we dereference
> src_pfns, dst_pfns or dma_addrs, the null pointer dereference bugs
> will happen.
> 
> Moreover, the GPU is going away. If the kcalloc() fails, we could not
> evict all pages mapping a chunk. So this patch adds a __GFP_NOFAIL
> flag in kcalloc().
> 
> Fixes: 249881232e14 ("nouveau/dmem: evict device private memory during release")
> Signed-off-by: Duoming Zhou <duoming@zju.edu.cn>
> ---
> Changes in v2:
>    - Allocate with __GFP_NOFAIL.
> 
>   drivers/gpu/drm/nouveau/nouveau_dmem.c | 6 +++---
>   1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/gpu/drm/nouveau/nouveau_dmem.c b/drivers/gpu/drm/nouveau/nouveau_dmem.c
> index 12feecf71e7..f5ae9724ee2 100644
> --- a/drivers/gpu/drm/nouveau/nouveau_dmem.c
> +++ b/drivers/gpu/drm/nouveau/nouveau_dmem.c
> @@ -378,9 +378,9 @@ nouveau_dmem_evict_chunk(struct nouveau_dmem_chunk *chunk)
>   	dma_addr_t *dma_addrs;
>   	struct nouveau_fence *fence;
>   
> -	src_pfns = kcalloc(npages, sizeof(*src_pfns), GFP_KERNEL);
> -	dst_pfns = kcalloc(npages, sizeof(*dst_pfns), GFP_KERNEL);
> -	dma_addrs = kcalloc(npages, sizeof(*dma_addrs), GFP_KERNEL);
> +	src_pfns = kcalloc(npages, sizeof(*src_pfns), GFP_KERNEL | __GFP_NOFAIL);
> +	dst_pfns = kcalloc(npages, sizeof(*dst_pfns), GFP_KERNEL | __GFP_NOFAIL);
> +	dma_addrs = kcalloc(npages, sizeof(*dma_addrs), GFP_KERNEL | __GFP_NOFAIL);

I think we should also switch to kvcalloc(), AFAICS we don't need 
physically contiguous memory.

Sorry I did not mention that in V1 already.

- Danilo

>   
>   	migrate_device_range(src_pfns, chunk->pagemap.range.start >> PAGE_SHIFT,
>   			npages);