1 files changed, 19 insertions, 29 deletions

diff --git a/fs/exec.c b/fs/exec.c
index 950ebd43cdc..3a79d97ac23 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -561,7 +561,7 @@ static int exec_mmap(struct mm_struct *mm)
 	arch_pick_mmap_layout(mm);
 	if (old_mm) {
 		up_read(&old_mm->mmap_sem);
-		if (active_mm != old_mm) BUG();
+		BUG_ON(active_mm != old_mm);
 		mmput(old_mm);
 		return 0;
 	}
@@ -665,9 +665,7 @@ static int de_thread(struct task_struct *tsk)
 	 * and to assume its PID:
 	 */
 	if (!thread_group_leader(current)) {
-		struct task_struct *parent;
 		struct dentry *proc_dentry1, *proc_dentry2;
-		unsigned long ptrace;
 
 		/*
 		 * Wait for the thread group leader to be a zombie.
@@ -678,6 +676,18 @@ static int de_thread(struct task_struct *tsk)
 		while (leader->exit_state != EXIT_ZOMBIE)
 			yield();
 
+		/*
+		 * The only record we have of the real-time age of a
+		 * process, regardless of execs it's done, is start_time.
+		 * All the past CPU time is accumulated in signal_struct
+		 * from sister threads now dead.  But in this non-leader
+		 * exec, nothing survives from the original leader thread,
+		 * whose birth marks the true age of this process now.
+		 * When we take on its identity by switching to its PID, we
+		 * also take its birthdate (always earlier than our own).
+		 */
+		current->start_time = leader->start_time;
+
 		spin_lock(&leader->proc_lock);
 		spin_lock(&current->proc_lock);
 		proc_dentry1 = proc_pid_unhash(current);
@@ -692,22 +702,6 @@ static int de_thread(struct task_struct *tsk)
 		 * two threads with a switched PID, and release
 		 * the former thread group leader:
 		 */
-		ptrace = leader->ptrace;
-		parent = leader->parent;
-		if (unlikely(ptrace) && unlikely(parent == current)) {
-			/*
-			 * Joker was ptracing his own group leader,
-			 * and now he wants to be his own parent!
-			 * We can't have that.
-			 */
-			ptrace = 0;
-		}
-
-		ptrace_unlink(current);
-		ptrace_unlink(leader);
-		remove_parent(current);
-		remove_parent(leader);
-
 
 		/* Become a process group leader with the old leader's pid.
 		 * Note: The old leader also uses thispid until release_task
@@ -718,19 +712,15 @@ static int de_thread(struct task_struct *tsk)
 		attach_pid(current, PIDTYPE_PID,  current->pid);
 		attach_pid(current, PIDTYPE_PGID, current->signal->pgrp);
 		attach_pid(current, PIDTYPE_SID,  current->signal->session);
-		list_add_tail(&current->tasks, &init_task.tasks);
+		list_add_tail_rcu(&current->tasks, &init_task.tasks);
 
-		current->parent = current->real_parent = leader->real_parent;
-		leader->parent = leader->real_parent = child_reaper;
 		current->group_leader = current;
-		leader->group_leader = leader;
+		leader->group_leader = current;
 
-		add_parent(current);
-		add_parent(leader);
-		if (ptrace) {
-			current->ptrace = ptrace;
-			__ptrace_link(current, parent);
-		}
+		/* Reduce leader to a thread */
+		detach_pid(leader, PIDTYPE_PGID);
+		detach_pid(leader, PIDTYPE_SID);
+		list_del_init(&leader->tasks);
 
 		current->exit_signal = SIGCHLD;