Merge branch 'core-fixes-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip

* 'core-fixes-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip:
sys: Fix missing rcu protection for __task_cred() access
signals: Fix more rcu assumptions
signal: Fix racy access to __task_cred in kill_pid_info_as_uid()

kernel/signal.c

···
 	struct user_struct *user;
 
 	/*
-	 * We won't get problems with the target's UID changing under us
-	 * because changing it requires RCU be used, and if t != current, the
-	 * caller must be holding the RCU readlock (by way of a spinlock) and
-	 * we use RCU protection here
+	 * Protect access to @t credentials. This can go away when all
+	 * callers hold rcu read lock.
 	 */
+	rcu_read_lock();
 	user = get_uid(__task_cred(t)->user);
 	atomic_inc(&user->sigpending);
+	rcu_read_unlock();
 
 	if (override_rlimit ||
 	    atomic_read(&user->sigpending) <=
···
 	int ret = -EINVAL;
 	struct task_struct *p;
 	const struct cred *pcred;
+	unsigned long flags;
 
 	if (!valid_signal(sig))
 		return ret;
 
-	read_lock(&tasklist_lock);
+	rcu_read_lock();
 	p = pid_task(pid, PIDTYPE_PID);
 	if (!p) {
 		ret = -ESRCH;
···
 	ret = security_task_kill(p, info, sig, secid);
 	if (ret)
 		goto out_unlock;
-	if (sig && p->sighand) {
-		unsigned long flags;
-		spin_lock_irqsave(&p->sighand->siglock, flags);
-		ret = __send_signal(sig, info, p, 1, 0);
-		spin_unlock_irqrestore(&p->sighand->siglock, flags);
+
+	if (sig) {
+		if (lock_task_sighand(p, &flags)) {
+			ret = __send_signal(sig, info, p, 1, 0);
+			unlock_task_sighand(p, &flags);
+		} else
+			ret = -ESRCH;
 	}
 out_unlock:
-	read_unlock(&tasklist_lock);
+	rcu_read_unlock();
 	return ret;
 }
 EXPORT_SYMBOL_GPL(kill_pid_info_as_uid);

kernel/sys.c

···
 	if (niceval > 19)
 		niceval = 19;
 
+	rcu_read_lock();
 	read_lock(&tasklist_lock);
 	switch (which) {
 		case PRIO_PROCESS:
···
 	}
 out_unlock:
 	read_unlock(&tasklist_lock);
+	rcu_read_unlock();
 out:
 	return error;
 }