[PATCH] SELinux fixups needed for preemptable RCU from -rt

["Paul E. McKenney" <paulmck@linux.vnet.ibm.com>]

Hello!

The attached patch needs to move from -rt to mainline given preemptable
RCU.  This patch fixes SELinux code that implicitly assumes that
disabling preemption prevents an RCU grace period from completing,
an assumption that is valid for Classic RCU, but not necessarily for
preemptable RCU.  Explicit rcu_read_lock() calls are thus added.

Pointed-out-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---

 security/selinux/avc.c   |    9 +++++++++
 security/selinux/netif.c |    2 ++
 2 files changed, 11 insertions(+)

Index: linux-2.6.24.4-rt4/security/selinux/avc.c
===================================================================
--- linux-2.6.24.4-rt4.orig/security/selinux/avc.c	2008-03-24 19:05:09.000000000 -0400
+++ linux-2.6.24.4-rt4/security/selinux/avc.c	2008-03-24 19:06:41.000000000 -0400
@@ -312,6 +312,7 @@ static inline int avc_reclaim_node(void)
 		if (!spin_trylock_irqsave(&avc_cache.slots_lock[hvalue], flags))
 			continue;
 
+		rcu_read_lock();
 		list_for_each_entry(node, &avc_cache.slots[hvalue], list) {
 			if (atomic_dec_and_test(&node->ae.used)) {
 				/* Recently Unused */
@@ -319,11 +320,13 @@ static inline int avc_reclaim_node(void)
 				avc_cache_stats_incr(reclaims);
 				ecx++;
 				if (ecx >= AVC_CACHE_RECLAIM) {
+					rcu_read_unlock();
 					spin_unlock_irqrestore(&avc_cache.slots_lock[hvalue], flags);
 					goto out;
 				}
 			}
 		}
+		rcu_read_unlock();
 		spin_unlock_irqrestore(&avc_cache.slots_lock[hvalue], flags);
 	}
 out:
@@ -807,8 +810,14 @@ int avc_ss_reset(u32 seqno)
 
 	for (i = 0; i < AVC_CACHE_SLOTS; i++) {
 		spin_lock_irqsave(&avc_cache.slots_lock[i], flag);
+		/*
+		 * On -rt the outer spinlock does not prevent RCU
+		 * from being performed:
+		 */
+		rcu_read_lock();
 		list_for_each_entry(node, &avc_cache.slots[i], list)
 			avc_node_delete(node);
+		rcu_read_unlock();
 		spin_unlock_irqrestore(&avc_cache.slots_lock[i], flag);
 	}
 
Index: linux-2.6.24.4-rt4/security/selinux/netif.c
===================================================================
--- linux-2.6.24.4-rt4.orig/security/selinux/netif.c	2008-03-24 19:05:09.000000000 -0400
+++ linux-2.6.24.4-rt4/security/selinux/netif.c	2008-03-24 19:06:41.000000000 -0400
@@ -210,6 +210,7 @@ static void sel_netif_flush(void)
 {
 	int idx;
 
+	rcu_read_lock();
 	spin_lock_bh(&sel_netif_lock);
 	for (idx = 0; idx < SEL_NETIF_HASH_SIZE; idx++) {
 		struct sel_netif *netif;
@@ -218,6 +219,7 @@ static void sel_netif_flush(void)
 			sel_netif_destroy(netif);
 	}
 	spin_unlock_bh(&sel_netif_lock);
+	rcu_read_unlock();
 }
 
 static int sel_netif_avc_callback(u32 event, u32 ssid, u32 tsid,