From: Paul E. McKenney <paulmck@us.ibm.com>
Date: Sun, 8 Jan 2006 09:01:38 +0000 (-0800)
Subject: [PATCH] Simpler signal-exit concurrency handling
X-Git-Tag: v2.6.16-rc1~840
X-Git-Url: https://err.no/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=2d89c929078588aa9b9c674ef03ee9aa816b59b8;p=linux-2.6

[PATCH] Simpler signal-exit concurrency handling

Some simplification in checking signal delivery against concurrent exit.
Instead of using get_task_struct_rcu(), which increments the task_struct
reference count, check the reference count after acquiring sighand lock.

Signed-off-by: "Paul E. McKenney" <paulmck@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
---

diff --git a/kernel/signal.c b/kernel/signal.c
index 64737c72da..9b6fda5e87 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -1102,18 +1102,19 @@ int group_send_sig_info(int sig, struct siginfo *info, struct task_struct *p)
 
 retry:
 	ret = check_kill_permission(sig, info, p);
-	if (!ret && sig && (sp = p->sighand)) {
-		if (!get_task_struct_rcu(p))
-			return -ESRCH;
+	if (!ret && sig && (sp = rcu_dereference(p->sighand))) {
 		spin_lock_irqsave(&sp->siglock, flags);
 		if (p->sighand != sp) {
 			spin_unlock_irqrestore(&sp->siglock, flags);
-			put_task_struct(p);
 			goto retry;
 		}
+		if ((atomic_read(&sp->count) == 0) ||
+				(atomic_read(&p->usage) == 0)) {
+			spin_unlock_irqrestore(&sp->siglock, flags);
+			return -ESRCH;
+		}
 		ret = __group_send_sig_info(sig, info, p);
 		spin_unlock_irqrestore(&sp->siglock, flags);
-		put_task_struct(p);
 	}
 
 	return ret;