From: Oleg Nesterov <oleg@redhat.com>
Date: Wed, 26 May 2010 21:43:11 +0000 (-0700)
Subject: exit: avoid sig->count in de_thread/__exit_signal synchronization
X-Git-Url: https://git.stricted.de/?a=commitdiff_plain;h=d344193a05da89c97e965da2c5cbf687d7385eae;p=GitHub%2Fexynos8895%2Fandroid_kernel_samsung_universal8895.git

exit: avoid sig->count in de_thread/__exit_signal synchronization

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>
---

diff --git a/fs/exec.c b/fs/exec.c
index 0c72d23ed0e2..e19de6a80339 100644
--- 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();
diff --git a/kernel/exit.c b/kernel/exit.c
index 59a104c673f7..9220967f4256 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -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)