[CRIU] [PATCH] restore: Defer new net-namespace creation until forked

[Andrew Vagin]

On Mon, Oct 27, 2014 at 07:19:03PM +0300, Cyrill Gorcunov wrote:
> Some kernel modules such as pktgen runs kthred upon
> new-net creation taking last_pid we were requested.
> Lets workaround this problem using clone + unshare
> bundle.
> 
> Signed-off-by: Cyrill Gorcunov <gorcunov at openvz.org>
> ---
>  cr-restore.c | 18 +++++++++++++++++-
>  1 file changed, 17 insertions(+), 1 deletion(-)
> 
> diff --git a/cr-restore.c b/cr-restore.c
> index d046f4bd0921..d3811cb7b5d7 100644
> --- a/cr-restore.c
> +++ b/cr-restore.c
> @@ -1086,8 +1086,16 @@ static inline int fork_with_pid(struct pstree_item *item)
>  		if (netns_pre_create())
>  			goto err_unlock;
>  
> +	/*
> +	 * Some kernel modules, such as netwrok packet generator
> +	 * run kernel thread upon net-namespace creattion taking
> +	 * the @pid we've been requeting via LAST_PID_PATH interface
> +	 * so that we can't restore a take with pid needed.
> +	 *
> +	 * Here is an idea -- unhare net namespace in callee instead.
> +	 */
>  	ret = clone(restore_task_with_children, ca.stack_ptr,
> -			ca.clone_flags | SIGCHLD, &ca);
> +		    (ca.clone_flags & ~CLONE_NEWNET) | SIGCHLD, &ca);
>  
>  	if (ret < 0) {
>  		pr_perror("Can't fork for %d", pid);
> @@ -1395,6 +1403,14 @@ static int restore_task_with_children(void *_arg)
>  	if ( !(ca->clone_flags & CLONE_FILES))
>  		close_safe(&ca->fd);
>  
> +	if (ca->clone_flags & CLONE_NEWNET) {
> +		ret = unshare(CLONE_NEWNET);
> +		if (ret) {
> +			pr_perror("Can't unshare net-namespace");
> +			goto err;
> +		}
> +	}

I would prefer to move this code after:
        if (current->pid.virt != pid) {
                pr_err("Pid %d do not match expected %d\n", pid, current->pid.virt);
                goto err;
        }

And now we doesn't support nested net namespaces, so we can have it in
the "Restore root task" blob.

> +
>  	if (current->state != TASK_HELPER) {
>  		ret = clone_service_fd(rsti(current)->service_fd_id);
>  		if (ret)
> -- 
> 1.9.3
>