[CRIU] [PATCH RFC] namespaces: use CLONE_VFORK with CLONE_VM when it is possible

[Kirill Tkhai]

Looks good

On 18.03.2017 01:29, Andrei Vagin wrote:
> From: Andrei Vagin <avagin at virtuozzo.com>
> 
> We use CLONE_VM to dump and restore namespaces. Currently we allocate
> a new stack, but CLONE_VFORK allows to work on the current stack, because
> a parent process is frozen while a child process is running.
> 
> Signed-off-by: Andrei Vagin <avagin at virtuozzo.com>

Reviewed-byL Kirill Tkhai <ktkhai at virtuozzo.com>

> ---
>  criu/clone-noasan.c |  8 ++++----
>  criu/namespaces.c   | 18 +++++-------------
>  2 files changed, 9 insertions(+), 17 deletions(-)
> 
> diff --git a/criu/clone-noasan.c b/criu/clone-noasan.c
> index c5171b1..1b19f3e 100644
> --- a/criu/clone-noasan.c
> +++ b/criu/clone-noasan.c
> @@ -19,13 +19,13 @@
>   */
>  int clone_noasan(int (*fn)(void *), int flags, void *arg)
>  {
> +	int ret;
>  	/*
>  	 * Reserve some space for clone() to locate arguments
> -	 * and retcode in this place
> +	 * and retcode in this place. stack_ptr is set out of the current used
> +	 * stack to be able to use CLONE_VFORK | CLONE_VM.
>  	 */
> -	char stack[128] __stack_aligned__;
> -	char *stack_ptr = &stack[sizeof(stack)];
> -	int ret;
> +	void *stack_ptr = (void *) round_down(((unsigned long) &ret) - 256, 16);
>  
>  	ret = clone(fn, stack_ptr, flags, arg);
>  	return ret;
> diff --git a/criu/namespaces.c b/criu/namespaces.c
> index a4c3063..f3bcbbd 100644
> --- a/criu/namespaces.c
> +++ b/criu/namespaces.c
> @@ -33,6 +33,7 @@
>  #include "common/scm.h"
>  #include "fdstore.h"
>  #include "proc_parse.h"
> +#include "clone-noasan.h"
>  
>  static struct ns_desc *ns_desc_array[] = {
>  	&net_ns_desc,
> @@ -985,19 +986,17 @@ static int dump_user_ns(void *arg)
>  
>  	if (switch_ns(ns->parent->ns_pid, &user_ns_desc, NULL) < 0) {
>  		pr_err("Can't enter user namespace\n");
> -		return -1;
> +		_exit(1);
>  	}
> -
> -	return __dump_user_ns(ns);
> +	_exit(__dump_user_ns(ns) == 0 ? 0 : 1);
>  }
>  
>  int collect_user_ns(struct ns_id *ns, void *oarg)
>  {
> -	int status, stack_size;
> +	int status;
>  	struct ns_id *p_ns;
>  	pid_t pid = -1;
>  	UsernsEntry *e;
> -	char *stack;
>  
>  	p_ns = ns->parent;
>  
> @@ -1026,13 +1025,7 @@ int collect_user_ns(struct ns_id *ns, void *oarg)
>  		 * may do changes about CRIU's internal files states in memory,
>  		 * so pass CLONE_FILES to reflect that.
>  		 */
> -		stack_size = 2 * 1024 * 1024;
> -		stack = mmap(NULL, stack_size, PROT_WRITE | PROT_READ, MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
> -		if (stack == MAP_FAILED) {
> -			pr_perror("Can't allocate stack");
> -			return -1;
> -		}
> -		pid = clone(dump_user_ns, stack + stack_size, CLONE_VM | CLONE_FILES | SIGCHLD, ns);
> +		pid = clone_noasan(dump_user_ns, CLONE_VM | CLONE_FILES | SIGCHLD | CLONE_VFORK, ns);
>  		if (pid == -1) {
>  			pr_perror("Can't clone");
>  			return -1;
> @@ -1045,7 +1038,6 @@ int collect_user_ns(struct ns_id *ns, void *oarg)
>  			pr_err("Can't dump nested user_ns: %x\n", status);
>  			return -1;
>  		}
> -		munmap(stack, stack_size);
>  		return 0;
>  	} else {
>  		if (__dump_user_ns(ns))
>