[CRIU] [PATCH] restore: block SIGCHILD for sub-processes (v2)

[Tycho Andersen]

On Mon, Oct 05, 2015 at 04:11:14PM +0300, Andrey Vagin wrote:
> From: Andrew Vagin <avagin at openvz.org>
> 
> Otherwise sigchld_handler() will call waitpid()
> and worries about unknown process.
> 
> (00.333012)      1: kernel/hostname nr 15
> (00.333120)      1: kernel/domainname nr 6
> (00.335243)      1: Error (cr-restore.c:1225): BUG at cr-restore.c:1225
> 
> v2: don't use unitialized oldmask
> 
> Cc: Tycho Andersen <tycho.andersen at canonical.com>

Acked-by: Tycho Andersen <tycho.andersen at canonical.com>

> Reported-by: Mr Jenkins
> Signed-off-by: Andrew Vagin <avagin at openvz.org>
> ---
>  sysctl.c | 14 +++++++++++++-
>  1 file changed, 13 insertions(+), 1 deletion(-)
> 
> diff --git a/sysctl.c b/sysctl.c
> index f074cca..f68dbe5 100644
> --- a/sysctl.c
> +++ b/sysctl.c
> @@ -198,6 +198,7 @@ static int __userns_sysctl_op(void *arg, int unused, pid_t pid)
>  	struct sysctl_userns_req *userns_req = arg;
>  	int op = userns_req->op;
>  	struct sysctl_req *req, **reqs = NULL;
> +	sigset_t blockmask, oldmask;
>  	pid_t worker;
>  
>  	// fix up the pointer
> @@ -268,6 +269,16 @@ static int __userns_sysctl_op(void *arg, int unused, pid_t pid)
>  		req = (struct sysctl_req *) (((char *) req) + total_len);
>  	}
>  
> +	/*
> +	 * Don't let the sigchld_handler() mess with us
> +	 * calling waitpid() on the exited worker. The
> +	 * same is done in cr_system().
> +	 */
> +
> +	sigemptyset(&blockmask);
> +	sigaddset(&blockmask, SIGCHLD);
> +	sigprocmask(SIG_BLOCK, &blockmask, &oldmask);
> +
>  	worker = fork();
>  	if (worker < 0)
>  		goto out;
> @@ -299,10 +310,11 @@ static int __userns_sysctl_op(void *arg, int unused, pid_t pid)
>  	}
>  
>  	if (waitpid(worker, &status, 0) != worker) {
> -		pr_err("worker didn't die?");
> +		pr_perror("worker didn't die?");
>  		kill(worker, SIGKILL);
>  		goto out;
>  	}
> +	sigprocmask(SIG_BLOCK, &oldmask, NULL);
>  
>  	if (!WIFEXITED(status) || WEXITSTATUS(status)) {
>  		pr_err("worker failed: %d\n", status);
> -- 
> 2.4.3
>