Re: main thread pthread_exit/sys_exit bug!

[Oleg Nesterov <oleg@redhat.com>]

On 02/09, Oleg Nesterov wrote:
>
> Yes sure. I meant, instead of just checking task_is_stopped_or_traced() in
> wait_consider_task(), we should do somthing like

In short, please see the "patch" below. I doubt it can be compiled,
just for the illustration.

Oleg.

--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -1417,6 +1417,19 @@ static int wait_task_zombie(struct task_
 	return retval;
 }
 
+static int *wait_xxx(struct task_struct *p, int ptrace)
+{
+	if (ptrace) {
+		if (task_is_stopped_or_traced(p))
+			return &p->exit_code;
+	} else {
+		if (p->signal->flags & SIGNAL_STOPPED_STOPPED)
+			return &p->signal->group_exit_code;
+	}
+
+	return NULL;
+}
+
 /*
  * Handle sys_wait4 work for one task in state TASK_STOPPED.  We hold
  * read_lock(&tasklist_lock) on entry.  If we return zero, we still hold
@@ -1427,7 +1440,7 @@ static int wait_task_stopped(int ptrace,
 			     int options, struct siginfo __user *infop,
 			     int __user *stat_addr, struct rusage __user *ru)
 {
-	int retval, exit_code, why;
+	int retval, exit_code, *p_code, why;
 	uid_t uid = 0; /* unneeded, required by compiler */
 	pid_t pid;
 
@@ -1437,22 +1450,16 @@ static int wait_task_stopped(int ptrace,
 	exit_code = 0;
 	spin_lock_irq(&p->sighand->siglock);
 
-	if (unlikely(!task_is_stopped_or_traced(p)))
-		goto unlock_sig;
-
-	if (!ptrace && p->signal->group_stop_count > 0)
-		/*
-		 * A group stop is in progress and this is the group leader.
-		 * We won't report until all threads have stopped.
-		 */
+	p_code = wait_xxx(p, ptrace);
+	if (unlikely(!p_code))
 		goto unlock_sig;
 
-	exit_code = p->exit_code;
+	exit_code = *p_code;
 	if (!exit_code)
 		goto unlock_sig;
 
 	if (!unlikely(options & WNOWAIT))
-		p->exit_code = 0;
+		*p_code = 0;
 
 	/* don't need the RCU readlock here as we're holding a spinlock */
 	uid = __task_cred(p)->uid;
@@ -1608,7 +1615,7 @@ static int wait_consider_task(struct tas
 	 */
 	*notask_error = 0;
 
-	if (task_is_stopped_or_traced(p))
+	if (wait_xxx(p, ptrace))
 		return wait_task_stopped(ptrace, p, options,
 					 infop, stat_addr, ru);