Re: [PATCH v3] drm/amdkfd: Fix error handling in criu_checkpoint

["Bhardwaj, Rajneesh" <rajneesh.bhardwaj@amd.com>]

This one is more elegant. Looks good to me!

Reviewed-and-tested-by: Rajneesh Bhardwaj <rajneesh.bhardwaj@amd.com>

On 11/3/2022 7:12 PM, Felix Kuehling wrote:
> Checkpoint BOs last. That way we don't need to close dmabuf FDs if
> something else fails later. This avoids problematic access to user mode
> memory in the error handling code path.
>
> criu_checkpoint_bos has its own error handling and cleanup that does not
> depend on access to user memory.
>
> In the private data, keep BOs before the remaining objects. This is
> necessary to restore things in the correct order as restoring events
> depends on the events-page BO being restored first.
>
> Fixes: be072b06c739 ("drm/amdkfd: CRIU export BOs as prime dmabuf objects")
> Reported-by: Jann Horn <jannh@google.com>
> CC: Rajneesh Bhardwaj <Rajneesh.Bhardwaj@amd.com>
> Signed-off-by: Felix Kuehling <Felix.Kuehling@amd.com>
>
> ---
>
> v3: Keep order of private data and restore order the same.
> ---
>   drivers/gpu/drm/amd/amdkfd/kfd_chardev.c | 34 +++++++++++-------------
>   1 file changed, 15 insertions(+), 19 deletions(-)
>
> diff --git a/drivers/gpu/drm/amd/amdkfd/kfd_chardev.c b/drivers/gpu/drm/amd/amdkfd/kfd_chardev.c
> index 5feaba6a77de..6d291aa6386b 100644
> --- a/drivers/gpu/drm/amd/amdkfd/kfd_chardev.c
> +++ b/drivers/gpu/drm/amd/amdkfd/kfd_chardev.c
> @@ -1950,7 +1950,7 @@ static int criu_checkpoint(struct file *filep,
>   {
>   	int ret;
>   	uint32_t num_devices, num_bos, num_objects;
> -	uint64_t priv_size, priv_offset = 0;
> +	uint64_t priv_size, priv_offset = 0, bo_priv_offset;
>   
>   	if (!args->devices || !args->bos || !args->priv_data)
>   		return -EINVAL;
> @@ -1994,38 +1994,34 @@ static int criu_checkpoint(struct file *filep,
>   	if (ret)
>   		goto exit_unlock;
>   
> -	ret = criu_checkpoint_bos(p, num_bos, (uint8_t __user *)args->bos,
> -			    (uint8_t __user *)args->priv_data, &priv_offset);
> -	if (ret)
> -		goto exit_unlock;
> +	/* Leave room for BOs in the private data. They need to be restored
> +	 * before events, but we checkpoint them last to simplify the error
> +	 * handling.
> +	 */
> +	bo_priv_offset = priv_offset;
> +	priv_offset += num_bos * sizeof(struct kfd_criu_bo_priv_data);
>   
>   	if (num_objects) {
>   		ret = kfd_criu_checkpoint_queues(p, (uint8_t __user *)args->priv_data,
>   						 &priv_offset);
>   		if (ret)
> -			goto close_bo_fds;
> +			goto exit_unlock;
>   
>   		ret = kfd_criu_checkpoint_events(p, (uint8_t __user *)args->priv_data,
>   						 &priv_offset);
>   		if (ret)
> -			goto close_bo_fds;
> +			goto exit_unlock;
>   
>   		ret = kfd_criu_checkpoint_svm(p, (uint8_t __user *)args->priv_data, &priv_offset);
>   		if (ret)
> -			goto close_bo_fds;
> +			goto exit_unlock;
>   	}
>   
> -close_bo_fds:
> -	if (ret) {
> -		/* If IOCTL returns err, user assumes all FDs opened in criu_dump_bos are closed */
> -		uint32_t i;
> -		struct kfd_criu_bo_bucket *bo_buckets = (struct kfd_criu_bo_bucket *) args->bos;
> -
> -		for (i = 0; i < num_bos; i++) {
> -			if (bo_buckets[i].alloc_flags & KFD_IOC_ALLOC_MEM_FLAGS_VRAM)
> -				close_fd(bo_buckets[i].dmabuf_fd);
> -		}
> -	}
> +	/* This must be the last thing in this function that can fail.
> +	 * Otherwise we leak dmabuf file descriptors.
> +	 */
> +	ret = criu_checkpoint_bos(p, num_bos, (uint8_t __user *)args->bos,
> +			   (uint8_t __user *)args->priv_data, &bo_priv_offset);
>   
>   exit_unlock:
>   	mutex_unlock(&p->mutex);