Merge branch 'ipv6-Another-followup-to-the-fib6_info-change'

David Ahern says:

====================
net/ipv6: Another followup to the fib6_info change

Last one - for this week.

Patches 1, 2 and 7 are more cleanup patches - removing dead code,
moving code from a header to near its single caller, and updating
function name.

Patches 3-5 do some refactoring leading up to patch 6 which fixes
a NULL dereference. I have only managed to trigger a panic once, so
I can not definitively confirm it addresses the problem but it seems
pretty clear that it is a race on removing a 'from' reference on
an rt6_info and another path using that 'from' value to do
cookie checking.
====================

Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/ip6_fib.h

@@ -174,7 +174,7 @@ struct fib6_info {
 
 struct rt6_info {
 	struct dst_entry		dst;
-	struct fib6_info		*from;
+	struct fib6_info __rcu		*from;
 
 	struct rt6key			rt6i_dst;
 	struct rt6key			rt6i_src;
@@ -223,39 +223,17 @@ static inline bool fib6_check_expired(const struct fib6_info *f6i)
 	return false;
 }
 
-static inline void rt6_clean_expires(struct rt6_info *rt)
-{
-	rt->rt6i_flags &= ~RTF_EXPIRES;
-	rt->dst.expires = 0;
-}
-
-static inline void rt6_set_expires(struct rt6_info *rt, unsigned long expires)
-{
-	rt->dst.expires = expires;
-	rt->rt6i_flags |= RTF_EXPIRES;
-}
-
-static inline void rt6_update_expires(struct rt6_info *rt0, int timeout)
-{
-	if (!(rt0->rt6i_flags & RTF_EXPIRES) && rt0->from)
-		rt0->dst.expires = rt0->from->expires;
-
-	dst_set_expires(&rt0->dst, timeout);
-	rt0->rt6i_flags |= RTF_EXPIRES;
-}
-
 /* Function to safely get fn->sernum for passed in rt
  * and store result in passed in cookie.
  * Return true if we can get cookie safely
  * Return false if not
  */
-static inline bool rt6_get_cookie_safe(const struct fib6_info *f6i,
-				       u32 *cookie)
+static inline bool fib6_get_cookie_safe(const struct fib6_info *f6i,
+					u32 *cookie)
 {
 	struct fib6_node *fn;
 	bool status = false;
 
-	rcu_read_lock();
 	fn = rcu_dereference(f6i->fib6_node);
 
 	if (fn) {
@@ -265,17 +243,22 @@ static inline bool rt6_get_cookie_safe(const struct fib6_info *f6i,
 		status = true;
 	}
 
-	rcu_read_unlock();
 	return status;
 }
 
 static inline u32 rt6_get_cookie(const struct rt6_info *rt)
 {
+	struct fib6_info *from;
 	u32 cookie = 0;
 
-	if (rt->rt6i_flags & RTF_PCPU ||
-	    (unlikely(!list_empty(&rt->rt6i_uncached)) && rt->from))
-		rt6_get_cookie_safe(rt->from, &cookie);
+	rcu_read_lock();
+
+	from = rcu_dereference(rt->from);
+	if (from && (rt->rt6i_flags & RTF_PCPU ||
+	    unlikely(!list_empty(&rt->rt6i_uncached))))
+		fib6_get_cookie_safe(from, &cookie);
+
+	rcu_read_unlock();
 
 	return cookie;
 }

net/ipv6/ip6_fib.c

@@ -860,6 +860,31 @@ static struct fib6_node *fib6_add_1(struct net *net,
 	return ln;
 }
 
+static void fib6_drop_pcpu_from(struct fib6_info *f6i,
+				const struct fib6_table *table)
+{
+	int cpu;
+
+	/* release the reference to this fib entry from
+	 * all of its cached pcpu routes
+	 */
+	for_each_possible_cpu(cpu) {
+		struct rt6_info **ppcpu_rt;
+		struct rt6_info *pcpu_rt;
+
+		ppcpu_rt = per_cpu_ptr(f6i->rt6i_pcpu, cpu);
+		pcpu_rt = *ppcpu_rt;
+		if (pcpu_rt) {
+			struct fib6_info *from;
+
+			from = rcu_dereference_protected(pcpu_rt->from,
+					     lockdep_is_held(&table->tb6_lock));
+			rcu_assign_pointer(pcpu_rt->from, NULL);
+			fib6_info_release(from);
+		}
+	}
+}
+
 static void fib6_purge_rt(struct fib6_info *rt, struct fib6_node *fn,
 			  struct net *net)
 {
@@ -887,24 +912,8 @@ static void fib6_purge_rt(struct fib6_info *rt, struct fib6_node *fn,
 				    lockdep_is_held(&table->tb6_lock));
 		}
 
-		if (rt->rt6i_pcpu) {
-			int cpu;
-
-			/* release the reference to this fib entry from
-			 * all of its cached pcpu routes
-			 */
-			for_each_possible_cpu(cpu) {
-				struct rt6_info **ppcpu_rt;
-				struct rt6_info *pcpu_rt;
-
-				ppcpu_rt = per_cpu_ptr(rt->rt6i_pcpu, cpu);
-				pcpu_rt = *ppcpu_rt;
-				if (pcpu_rt) {
-					fib6_info_release(pcpu_rt->from);
-					pcpu_rt->from = NULL;
-				}
-			}
-		}
+		if (rt->rt6i_pcpu)
+			fib6_drop_pcpu_from(rt, table);
 	}
 }
 

net/ipv6/ip6_output.c

@@ -962,16 +962,21 @@ static int ip6_dst_lookup_tail(struct net *net, const struct sock *sk,
 	 * that's why we try it again later.
 	 */
 	if (ipv6_addr_any(&fl6->saddr) && (!*dst || !(*dst)->error)) {
+		struct fib6_info *from;
 		struct rt6_info *rt;
 		bool had_dst = *dst != NULL;
 
 		if (!had_dst)
 			*dst = ip6_route_output(net, sk, fl6);
 		rt = (*dst)->error ? NULL : (struct rt6_info *)*dst;
-		err = ip6_route_get_saddr(net, rt ? rt->from : NULL,
-					  &fl6->daddr,
+
+		rcu_read_lock();
+		from = rt ? rcu_dereference(rt->from) : NULL;
+		err = ip6_route_get_saddr(net, from, &fl6->daddr,
 					  sk ? inet6_sk(sk)->srcprefs : 0,
 					  &fl6->saddr);
+		rcu_read_unlock();
+
 		if (err)
 			goto out_err_release;