[tip:core/urgent] signals: Fix more rcu assumptions

[tip-bot for Thomas Gleixner <tglx@linutronix.de>]

Commit-ID:  7cf7db8df0b78076eafa4ead47559344ca7b7a43
Gitweb:     http://git.kernel.org/tip/7cf7db8df0b78076eafa4ead47559344ca7b7a43
Author:     Thomas Gleixner <tglx@linutronix.de>
AuthorDate: Thu, 10 Dec 2009 00:53:21 +0000
Committer:  Thomas Gleixner <tglx@linutronix.de>
CommitDate: Thu, 10 Dec 2009 23:04:11 +0100

signals: Fix more rcu assumptions

1) Remove the misleading comment in __sigqueue_alloc() which claims
   that holding a spinlock is equivalent to rcu_read_lock().

2) Add a rcu_read_lock/unlock around the __task_cred() access
   in __sigqueue_alloc()

This needs to be revisited to remove the remaining users of
read_lock(&tasklist_lock) but that's outside the scope of this patch.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
LKML-Reference: <20091210004703.269843657@linutronix.de>
---
 kernel/signal.c |    8 ++++----
 1 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/kernel/signal.c b/kernel/signal.c
index 7331656..f67545f 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -218,13 +218,13 @@ __sigqueue_alloc(int sig, struct task_struct *t, gfp_t flags, int override_rlimi
 	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) <=