[PATCH] coredump: shutdown current process first

This patch optimizes zap_threads() for the case when there are no ->mm
users except the current's thread group.  In that case we can avoid
'for_each_process()' loop.

It also adds a useful invariant: SIGNAL_GROUP_EXIT (if checked under
->siglock) always implies that all threads (except may be current) have
pending SIGKILL.

Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Cc: Roland McGrath <roland@redhat.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 17 insertions, 12 deletions

diff --git a/fs/exec.c b/fs/exec.c
index 8c8f2894949d..c8494f513eaf 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -1371,13 +1371,7 @@ static void format_corename(char *corename, const char *pattern, long signr)
 static void zap_process(struct task_struct *start)
 {
         struct task_struct *t;
-        unsigned long flags;
 
-        /*
-         * start->sighand can't disappear, but may be
-         * changed by de_thread()
-         */
-        lock_task_sighand(start, &flags);
         start->signal->flags = SIGNAL_GROUP_EXIT;
         start->signal->group_stop_count = 0;
 
@@ -1389,40 +1383,51 @@ static void zap_process(struct task_struct *start)
                         signal_wake_up(t, 1);
                 }
         } while ((t = next_thread(t)) != start);
-
-        unlock_task_sighand(start, &flags);
 }
 
 static inline int zap_threads(struct task_struct *tsk, struct mm_struct *mm,
                                 int exit_code)
 {
         struct task_struct *g, *p;
+        unsigned long flags;
         int err = -EAGAIN;
 
         spin_lock_irq(&tsk->sighand->siglock);
         if (!(tsk->signal->flags & SIGNAL_GROUP_EXIT)) {
-                tsk->signal->flags = SIGNAL_GROUP_EXIT;
                 tsk->signal->group_exit_code = exit_code;
-                tsk->signal->group_stop_count = 0;
+                zap_process(tsk);
                 err = 0;
         }
         spin_unlock_irq(&tsk->sighand->siglock);
         if (err)
                 return err;
 
+        if (atomic_read(&mm->mm_users) == mm->core_waiters + 1)
+                goto done;
+
         rcu_read_lock();
         for_each_process(g) {
+                if (g == tsk->group_leader)
+                        continue;
+
                 p = g;
                 do {
                         if (p->mm) {
-                                if (p->mm == mm)
+                                if (p->mm == mm) {
+                                        /*
+                                         * p->sighand can't disappear, but
+                                         * may be changed by de_thread()
+                                         */
+                                        lock_task_sighand(p, &flags);
                                         zap_process(p);
+                                        unlock_task_sighand(p, &flags);
+                                }
                                 break;
                         }
                 } while ((p = next_thread(p)) != g);
         }
         rcu_read_unlock();
-
+done:
         return mm->core_waiters;
 }