Re: [PATCH] drm/panthor: Lock the VM resv before calling drm_gpuvm_bo_obtain_prealloc()

[Steven Price <steven.price@arm.com>]

On 13/09/2024 12:27, Boris Brezillon wrote:
> drm_gpuvm_bo_obtain_prealloc() will call drm_gpuvm_bo_put() on our
> pre-allocated BO if the <BO,VM> association exists. Given we
> only have one ref on preallocated_vm_bo, drm_gpuvm_bo_destroy() will
> be called immediately, and we have to hold the VM resv lock when
> calling this function.
> 
> Fixes: 647810ec2476 ("drm/panthor: Add the MMU/VM logical block")
> Signed-off-by: Boris Brezillon <boris.brezillon@collabora.com>

Reviewed-by: Steven Price <steven.price@arm.com>

> ---
>  drivers/gpu/drm/panthor/panthor_mmu.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/drivers/gpu/drm/panthor/panthor_mmu.c b/drivers/gpu/drm/panthor/panthor_mmu.c
> index 37f1885c54c7..aa12ed2acfcf 100644
> --- a/drivers/gpu/drm/panthor/panthor_mmu.c
> +++ b/drivers/gpu/drm/panthor/panthor_mmu.c
> @@ -1251,9 +1251,17 @@ static int panthor_vm_prepare_map_op_ctx(struct panthor_vm_op_ctx *op_ctx,
>  		goto err_cleanup;
>  	}
>  
> +	/* drm_gpuvm_bo_obtain_prealloc() will call drm_gpuvm_bo_put() on our
> +	 * pre-allocated BO if the <BO,VM> association exists. Given we
> +	 * only have one ref on preallocated_vm_bo, drm_gpuvm_bo_destroy() will
> +	 * be called immediately, and we have to hold the VM resv lock when
> +	 * calling this function.
> +	 */
> +	dma_resv_lock(panthor_vm_resv(vm), NULL);
>  	mutex_lock(&bo->gpuva_list_lock);
>  	op_ctx->map.vm_bo = drm_gpuvm_bo_obtain_prealloc(preallocated_vm_bo);
>  	mutex_unlock(&bo->gpuva_list_lock);
> +	dma_resv_unlock(panthor_vm_resv(vm));
>  
>  	/* If the a vm_bo for this <VM,BO> combination exists, it already
>  	 * retains a pin ref, and we can release the one we took earlier.