[CRIU] [PATCH] util: block SIGCHLD to run a sub process

[Kirill Tkhai]

On 30.03.2017 08:48, Andrei Vagin wrote:
> From: Andrei Vagin <avagin at virtuozzo.com>
> 
> CRIU sets a sigchld handler and calls waitpid from it,
> but when we call a sub-process, we want to wait it
> 
> Cc: Kirill Tkhai <ktkhai at virtuozzo.com>
> Signed-off-by: Andrei Vagin <avagin at virtuozzo.com>

Ok for idea, but, please, see comments below.

> ---
>  criu/util.c | 26 +++++++++++++++++++++++---
>  1 file changed, 23 insertions(+), 3 deletions(-)
> 
> diff --git a/criu/util.c b/criu/util.c
> index 558d498..c014a5d 100644
> --- a/criu/util.c
> +++ b/criu/util.c
> @@ -1369,6 +1369,7 @@ int open_fd_of_real_pid(pid_t pid, int fd, int flags)
>  
>  int call_in_child_process(int (*fn)(void *), void *arg)
>  {
> +	sigset_t blockmask, oldmask;
>  	int size, status, ret = -1;
>  	char *stack;
>  	pid_t pid;
> @@ -1379,14 +1380,27 @@ int call_in_child_process(int (*fn)(void *), void *arg)
>  		pr_perror("Can't allocate stack");
>  		return -1;
>  	}
> +
> +	sigemptyset(&blockmask);
> +	sigaddset(&blockmask, SIGCHLD);
> +
> +	if (sigprocmask(SIG_BLOCK, &blockmask, &oldmask) == -1) {
> +		pr_perror("Can not set mask of blocked signals");
> +		goto out_munmap;
> +	}
> +
>  	pid = clone(fn, stack + size, CLONE_VM | CLONE_FILES | SIGCHLD, arg);
>  	if (pid == -1) {
>  		pr_perror("Can't clone");
> -		goto out_munmap;
> +		goto out_unblock;
>  	}
>  	errno = 0;

Not need to clear errno, if there are two separate "if" and "pr_perror".

> -	if (waitpid(pid, &status, 0) != pid || !WIFEXITED(status) || WEXITSTATUS(status)) {
> -		pr_err("Can't wait or bad status: errno=%d, status=%d", errno, status);
> +	if (waitpid(pid, &status, 0) != pid) {
> +		pr_perror("Unable to wait %d", pid);
> +		goto out_close;
> +	}
> +	if ( !WIFEXITED(status) || WEXITSTATUS(status)) {
> +		pr_err("Can't wait or bad status: errno=%d (%s), status=%d", errno, strerror(errno), status);

Not need to print errno as it's already in the first "if".

>  		goto out_close;
>  	}
>  	ret = 0;
> @@ -1396,8 +1410,14 @@ out_close:
>  	 * with the same pid later, it will try to reuse this /proc/self.
>  	 */
>  	close_pid_proc();
> +out_unblock:
> +	if (sigprocmask(SIG_SETMASK, &oldmask, NULL) == -1) {
> +		pr_perror("Can not unset mask of blocked signals");
> +		ret = -1;
> +	}
>  out_munmap:
>  	munmap(stack, size);
> +
>  	return ret;
>  }
>  
>