exit: Use the correct exit_code in /proc/<pid>/stat

Since do_proc_statt was modified to return process wide values instead
of per task values the exit_code calculation has never been updated.
Update it now to return the process wide exit_code when it is requested
and available.

History-Tree: https://git.kernel.org/pub/scm/linux/kernel/git/tglx/history.git
Fixes: bf719d2 ("[PATCH] distinct tgid/tid CPU usage")
Link: https://lkml.kernel.org/r/20220103213312.9144-4-ebiederm@xmission.com
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>

Author: ebiederm

fs/proc/array.c

@@ -468,6 +468,7 @@ static int do_task_stat(struct seq_file *m, struct pid_namespace *ns,
 	u64 cgtime, gtime;
 	unsigned long rsslim = 0;
 	unsigned long flags;
+	int exit_code = task->exit_code;
 
 	state = *get_task_state(task);
 	vsize = eip = esp = 0;
@@ -531,6 +532,9 @@ static int do_task_stat(struct seq_file *m, struct pid_namespace *ns,
 			maj_flt += sig->maj_flt;
 			thread_group_cputime_adjusted(task, &utime, &stime);
 			gtime += sig->gtime;
+
+			if (sig->flags & (SIGNAL_GROUP_EXIT | SIGNAL_STOP_STOPPED))
+				exit_code = sig->group_exit_code;
 		}
 
 		sid = task_session_nr_ns(task, ns);
@@ -630,7 +634,7 @@ static int do_task_stat(struct seq_file *m, struct pid_namespace *ns,
 		seq_puts(m, " 0 0 0 0 0 0 0");
 
 	if (permitted)
-		seq_put_decimal_ll(m, " ", task->exit_code);
+		seq_put_decimal_ll(m, " ", exit_code);
 	else
 		seq_puts(m, " 0");