[CRIU] [PATCH] restorer: block signals before restoring SIGCHLD handler

[Pavel Emelyanov]

On 09/20/2013 06:21 PM, Andrey Vagin wrote:
> Otherwise the process can handler this signal before calling sigreturn.
> 
> And threads must block signals before switching on
> CR_STATE_RESTORE_SIGCHLD, because signals are restoring on this stage.
> 
> So if a thread leader starts restoring shared signals before another
> thread has blocked signals, this thread can start to hadle the signal.
> I have seen this race in static/sigpending.

What race? Plz, elaborate.

> Signed-off-by: Andrey Vagin <avagin at openvz.org>
> ---
>  pie/restorer.c | 25 +++++++++++++++++--------
>  1 file changed, 17 insertions(+), 8 deletions(-)
> 
> diff --git a/pie/restorer.c b/pie/restorer.c
> index 95bb63f..cc58584 100644
> --- a/pie/restorer.c
> +++ b/pie/restorer.c
> @@ -211,14 +211,6 @@ static void restore_rlims(struct task_restore_core_args *ta)
>  static int restore_signals(siginfo_t *ptr, int nr, bool group)
>  {
>  	int ret, i;
> -	k_rtsigset_t to_block;
> -
> -	ksigfillset(&to_block);
> -	ret = sys_sigprocmask(SIG_SETMASK, &to_block, NULL, sizeof(k_rtsigset_t));
> -	if (ret) {
> -		pr_err("Unable to block signals %d", ret);
> -		return -1;
> -	}
>  
>  	for (i = 0; i < nr; i++) {
>  		siginfo_t *info = ptr + i;
> @@ -272,6 +264,7 @@ static int restore_thread_common(struct rt_sigframe *sigframe,
>  long __export_restore_thread(struct thread_restore_args *args)
>  {
>  	struct rt_sigframe *rt_sigframe;
> +	k_rtsigset_t to_block;
>  	unsigned long new_sp;
>  	int my_pid = sys_gettid();
>  	int ret;
> @@ -281,6 +274,14 @@ long __export_restore_thread(struct thread_restore_args *args)
>  		goto core_restore_end;
>  	}
>  
> +	/* All signals must be handled by thread leader */
> +	ksigfillset(&to_block);
> +	ret = sys_sigprocmask(SIG_SETMASK, &to_block, NULL, sizeof(k_rtsigset_t));
> +	if (ret) {
> +		pr_err("Unable to block signals %d", ret);
> +		goto core_restore_end;
> +	}
> +
>  	rt_sigframe = (void *)args->mem_zone.rt_sigframe;
>  
>  	if (restore_thread_common(rt_sigframe, args))
> @@ -568,6 +569,7 @@ long __export_restore_task(struct task_restore_core_args *args)
>  
>  	struct rt_sigframe *rt_sigframe;
>  	unsigned long new_sp;
> +	k_rtsigset_t to_block;
>  	pid_t my_pid = sys_getpid();
>  	rt_sigaction_t act;
>  
> @@ -853,6 +855,13 @@ long __export_restore_task(struct task_restore_core_args *args)
>  
>  	futex_wait_while_gt(&zombies_inprogress, 0);
>  
> +	ksigfillset(&to_block);
> +	ret = sys_sigprocmask(SIG_SETMASK, &to_block, NULL, sizeof(k_rtsigset_t));
> +	if (ret) {
> +		pr_err("Unable to block signals %ld", ret);
> +		goto core_restore_end;
> +	}
> +
>  	sys_sigaction(SIGCHLD, &args->sigchld_act, NULL, sizeof(k_rtsigset_t));
>  
>  	ret = restore_signals(args->siginfo, args->siginfo_nr, true);
>