coredump: set ->group_exit_code for other CLONE_VM tasks too

User visible change.

do_coredump() kills all threads which share the same ->mm but only the
coredumping process gets the proper exit_code.  Other tasks which share
the same ->mm die "silently" and return status == 0 to parent.

This is historical behaviour, not actually a bug.  But I think Frank
Heckenbach rightly dislikes the current behaviour.  Simple test-case:

	#include <stdio.h>
	#include <unistd.h>
	#include <signal.h>
	#include <sys/wait.h>

	int main(void)
	{
		int stat;

		if (!fork()) {
			if (!vfork())
				kill(getpid(), SIGQUIT);
		}

		wait(&stat);
		printf("stat=%x\n", stat);
		return 0;
	}

Before this patch it prints "stat=0" despite the fact the child was killed
by SIGQUIT.  After this patch the output is "stat=3" which obviously makes
more sense.

Even with this patch, only the task which originates the coredumping gets
"|= 0x80" if the core was actually dumped, but at least the coredumping
signal is visible to do_wait/etc.
Reported-by: Frank Heckenbach <f.heckenbach@fh-soft.de>
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: WANG Cong <xiyou.wangcong@gmail.com>
Cc: Roland McGrath <roland@redhat.com>
Cc: Neil Horman <nhorman@tuxdriver.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/exec.c

@@ -1561,12 +1561,13 @@ out:
 	return ispipe;
 }
 
-static int zap_process(struct task_struct *start)
+static int zap_process(struct task_struct *start, int exit_code)
 {
 	struct task_struct *t;
 	int nr = 0;
 
 	start->signal->flags = SIGNAL_GROUP_EXIT;
+	start->signal->group_exit_code = exit_code;
 	start->signal->group_stop_count = 0;
 
 	t = start;
@@ -1591,8 +1592,7 @@ static inline int zap_threads(struct task_struct *tsk, struct mm_struct *mm,
 	spin_lock_irq(&tsk->sighand->siglock);
 	if (!signal_group_exit(tsk->signal)) {
 		mm->core_state = core_state;
-		tsk->signal->group_exit_code = exit_code;
-		nr = zap_process(tsk);
+		nr = zap_process(tsk, exit_code);
 	}
 	spin_unlock_irq(&tsk->sighand->siglock);
 	if (unlikely(nr < 0))
@@ -1641,7 +1641,7 @@ static inline int zap_threads(struct task_struct *tsk, struct mm_struct *mm,
 			if (p->mm) {
 				if (unlikely(p->mm == mm)) {
 					lock_task_sighand(p, &flags);
-					nr += zap_process(p);
+					nr += zap_process(p, exit_code);
 					unlock_task_sighand(p, &flags);
 				}
 				break;