[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>

diff --git a/fs/exec.c b/fs/exec.c
index 8c8f2894949da8374450e52376f3528b9038b3c0..c8494f513eaf578ce674e74219597f7d6f6b47ec 100644 (file)
--- 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;
 }