[PATCH] process accounting: take original leader's start_time in non-leader exec

[sfrench/cifs-2.6.git] / fs / exec.c

diff --git a/fs/exec.c b/fs/exec.c
index 950ebd43cdc35dd2503214db36289dddb5f26250..3234a0c32d5405bdfd8f46f97cd97994e93828ee 100644 (file)
--- 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;
        }
@@ -678,6 +678,18 @@ 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);
@@ -723,7 +735,12 @@ static int de_thread(struct task_struct *tsk)
                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;
+
+               /* Reduce leader to a thread */
+               detach_pid(leader, PIDTYPE_PGID);
+               detach_pid(leader, PIDTYPE_SID);
+               list_del_init(&leader->tasks);
 
                add_parent(current);
                add_parent(leader);