linux-kernel - Re: [PATCH] [RFC] fix missed SIGCONT cases

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Date:	Fri, 29 Feb 2008 16:20:30 +0300
From:	Oleg Nesterov <oleg@...sign.ru>
To:	Roland McGrath <roland@...hat.com>
Cc:	Jiri Kosina <jkosina@...e.cz>,
	Davide Libenzi <davidel@...ilserver.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] [RFC] fix missed SIGCONT cases

On 02/29, Oleg Nesterov wrote:
>
> On 02/28, Roland McGrath wrote:
> >
> > I don't dislike the direction of your flag-setting approach above.  But
> > it does introduce more new subtleties that warrant more thought.
>
> Yes sure.

Still. The more I think about it, the more I like it. It is so simple,
and allows us to do further cleanups. Please look at the patch below.
Now we don't need tasklist to send the signal.

handle_stop_signal() should be cleanuped as you pointed out, but this
patch only does the requied minimum.

I am worried about ptrace, but hopefully there is no problem.

Oleg.

--- 25/include/linux/sched.h~SIG_NP	2008-02-25 19:13:05.000000000 +0300
+++ 25/include/linux/sched.h	2008-02-29 15:38:00.000000000 +0300
@@ -455,6 +455,8 @@ struct signal_struct {
 	int			group_stop_count;
 	unsigned int		flags; /* see SIGNAL_* flags below */
 
+	unsigned int		notify_parent; /* will be moved into ->flags */
+
 	/* POSIX.1b Interval Timers */
 	struct list_head posix_timers;
 
--- 25/kernel/signal.c~SIG_NP	2008-02-29 15:28:28.000000000 +0300
+++ 25/kernel/signal.c	2008-02-29 15:54:54.000000000 +0300
@@ -597,9 +597,7 @@ static void handle_stop_signal(int sig, 
 			 */
 			p->signal->group_stop_count = 0;
 			p->signal->flags = SIGNAL_STOP_CONTINUED;
-			spin_unlock(&p->sighand->siglock);
-			do_notify_parent_cldstop(p, CLD_STOPPED);
-			spin_lock(&p->sighand->siglock);
+			p->signal->notify_parent = CLD_STOPPED;
 		}
 		rm_from_queue(SIG_KERNEL_STOP_MASK, &p->signal->shared_pending);
 		t = p;
@@ -638,9 +636,7 @@ static void handle_stop_signal(int sig, 
 			 */
 			p->signal->flags = SIGNAL_STOP_CONTINUED;
 			p->signal->group_exit_code = 0;
-			spin_unlock(&p->sighand->siglock);
-			do_notify_parent_cldstop(p, CLD_CONTINUED);
-			spin_lock(&p->sighand->siglock);
+			p->signal->notify_parent = CLD_CONTINUED;
 		} else {
 			/*
 			 * We are not stopped, but there could be a stop
@@ -1748,6 +1744,21 @@ static int do_signal_stop(int signr)
 	return 1;
 }
 
+static int handle_notify_parent(void)
+{
+	int why = current->signal->notify_parent;
+	if (likely(!why))
+		return 0;
+	current->signal->notify_parent = 0;
+	spin_unlock_irq(&current->sighand->siglock);
+
+	read_lock(&tasklist_lock);
+	do_notify_parent_cldstop(current, why);
+	read_unlock(&tasklist_lock);
+
+	return 1;
+}
+
 int get_signal_to_deliver(siginfo_t *info, struct k_sigaction *return_ka,
 			  struct pt_regs *regs, void *cookie)
 {
@@ -1761,6 +1772,9 @@ relock:
 	for (;;) {
 		struct k_sigaction *ka;
 
+		if (unlikely(handle_notify_parent()))
+			goto relock;
+
 		if (unlikely(current->signal->group_stop_count > 0) &&
 		    do_signal_stop(0))
 			goto relock;

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