exit: avoid sig->count in de_thread/__exit_signal synchronization
Oleg Nesterov [Wed, 26 May 2010 21:43:11 +0000 (14:43 -0700)]
de_thread() and __exit_signal() use signal_struct->count/notify_count for
synchronization.  We can simplify the code and use ->notify_count only.
Instead of comparing these two counters, we can change de_thread() to set
->notify_count = nr_of_sub_threads, then change __exit_signal() to
dec-and-test this counter and notify group_exit_task.

Note that __exit_signal() checks "notify_count > 0" just for symmetry with
exit_notify(), we could just check it is != 0.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: Roland McGrath <roland@redhat.com>
Cc: Veaceslav Falico <vfalico@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/exec.c
kernel/exit.c

index 0c72d23..e19de6a 100644 (file)
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -768,7 +768,6 @@ static int de_thread(struct task_struct *tsk)
        struct signal_struct *sig = tsk->signal;
        struct sighand_struct *oldsighand = tsk->sighand;
        spinlock_t *lock = &oldsighand->siglock;
-       int count;
 
        if (thread_group_empty(tsk))
                goto no_thread_group;
@@ -785,13 +784,13 @@ static int de_thread(struct task_struct *tsk)
                spin_unlock_irq(lock);
                return -EAGAIN;
        }
+
        sig->group_exit_task = tsk;
-       zap_other_threads(tsk);
+       sig->notify_count = zap_other_threads(tsk);
+       if (!thread_group_leader(tsk))
+               sig->notify_count--;
 
-       /* Account for the thread group leader hanging around: */
-       count = thread_group_leader(tsk) ? 1 : 2;
-       sig->notify_count = count;
-       while (atomic_read(&sig->count) > count) {
+       while (sig->notify_count) {
                __set_current_state(TASK_UNINTERRUPTIBLE);
                spin_unlock_irq(lock);
                schedule();
index 59a104c..9220967 100644 (file)
@@ -97,7 +97,7 @@ static void __exit_signal(struct task_struct *tsk)
                 * If there is any task waiting for the group exit
                 * then notify it:
                 */
-               if (sig->group_exit_task && atomic_read(&sig->count) == sig->notify_count)
+               if (sig->notify_count > 0 && !--sig->notify_count)
                        wake_up_process(sig->group_exit_task);
 
                if (tsk == sig->curr_target)