[Devel] Re: [PATCH] Signal semantics for /sbin/init

[Dave Hansen]

On Sat, 2007-10-27 at 12:00 -0700, sukadev at us.ibm.com wrote:
> +static int sig_init_ignore(struct task_struct *tsk)
> +{
> -static int sig_ignored(struct task_struct *t, int sig)
> +	// Currently this check is a bit racy with exec(),
> +	// we can _simplify_ de_thread and close the race.
> +	if (likely(!is_global_init(tsk->group_leader)))
> +		return 0;
> +
> +	return 1;
> +}

Umm.  C++ comments? ;)

Also, I'm not sure an out-of-line function this small really needs a
likely/unlikely hint.  Seems like a waste of the bytes to me.

> +static int sig_task_ignore(struct task_struct *tsk, int sig)
>  {
> -	void __user * handler;
> +	void __user * handler = tsk->sighand->action[sig-1].sa.sa_handler;
> +
> +	if (handler == SIG_IGN)
> +		return 1;

Something simple like:
/*
 * ensure that the process is expecting to get this signal,
 * and thus won't get SIG_...
 */
Would be helpful to understand your motivation here.

> +	if (handler != SIG_DFL)
> +		return 0;
> 
> +	return sig_kernel_ignore(sig) || sig_init_ignore(tsk);
> +}

> +static int sig_ignored(struct task_struct *t, int sig)
> +{
>  	/*
>  	 * Tracers always want to know about signals..
>  	 */
> @@ -58,10 +80,7 @@ static int sig_ignored(struct task_struc
>  	if (sigismember(&t->blocked, sig))
>  		return 0;
> 
> -	/* Is it explicitly or implicitly ignored? */
> -	handler = t->sighand->action[sig-1].sa.sa_handler;
> -	return   handler == SIG_IGN ||
> -		(handler == SIG_DFL && sig_kernel_ignore(sig));
> +	return sig_task_ignore(t, sig);
>  }

And technically, your helper patch could be separated out from the rest
here.  It isn't a huge deal, but it would be nice.

>  /*
> @@ -566,6 +585,9 @@ static void handle_stop_signal(int sig, 
>  		 */
>  		return;
> 
> +	if (sig_init_ignore(p))
> +		return;

The function name isn't quite good enough to understand why this is
here.  Quick comment, maybe?

>  	if (sig_kernel_stop(sig)) {
>  		/*
>  		 * This is a stop signal.  Remove SIGCONT from all queues.
> @@ -1860,12 +1882,6 @@ relock:
>  		if (sig_kernel_ignore(signr)) /* Default is nothing. */
>  			continue;
> 
> -		/*
> -		 * Global init gets no signals it doesn't want.
> -		 */
> -		if (is_global_init(current))
> -			continue;
> -
>  		if (sig_kernel_stop(signr)) {
>  			/*
>  			 * The default action is to stop all threads in
> @@ -2317,6 +2333,7 @@ int do_sigaction(int sig, struct k_sigac
>  	k = &current->sighand->action[sig-1];
> 
>  	spin_lock_irq(&current->sighand->siglock);
> +
>  	if (oact)
>  		*oact = *k;

Fix that, please.

> @@ -2335,8 +2352,7 @@ int do_sigaction(int sig, struct k_sigac
>  		 *   (for example, SIGCHLD), shall cause the pending signal to
>  		 *   be discarded, whether or not it is blocked"
>  		 */
> -		if (act->sa.sa_handler == SIG_IGN ||
> -		   (act->sa.sa_handler == SIG_DFL && sig_kernel_ignore(sig))) {
> +		if (sig_task_ignore(current, sig)) {
>  			struct task_struct *t = current;
>  			sigemptyset(&mask);
>  			sigaddset(&mask, sig);
-- Dave

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