ipv6: convert fib6_ref to refcount_t

We suspect some issues involving fib6_ref 0 -> 1 transitions might
cause strange syzbot reports.

Lets convert fib6_ref to refcount_t to catch them earlier.
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Wei Wang <weiwan@google.com>
Acked-by: Wei Wang <weiwan@google.com>
Reviewed-by: David Ahern <dsahern@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/ip6_fib.h

@@ -146,7 +146,7 @@ struct fib6_info {
 	struct list_head		fib6_siblings;
 	unsigned int			fib6_nsiblings;
 
-	atomic_t			fib6_ref;
+	refcount_t			fib6_ref;
 	unsigned long			expires;
 	struct dst_metrics		*fib6_metrics;
 #define fib6_pmtu		fib6_metrics->metrics[RTAX_MTU-1]
@@ -284,17 +284,17 @@ void fib6_info_destroy_rcu(struct rcu_head *head);
 
 static inline void fib6_info_hold(struct fib6_info *f6i)
 {
-	atomic_inc(&f6i->fib6_ref);
+	refcount_inc(&f6i->fib6_ref);
 }
 
 static inline bool fib6_info_hold_safe(struct fib6_info *f6i)
 {
-	return atomic_inc_not_zero(&f6i->fib6_ref);
+	return refcount_inc_not_zero(&f6i->fib6_ref);
 }
 
 static inline void fib6_info_release(struct fib6_info *f6i)
 {
-	if (f6i && atomic_dec_and_test(&f6i->fib6_ref))
+	if (f6i && refcount_dec_and_test(&f6i->fib6_ref))
 		call_rcu(&f6i->rcu, fib6_info_destroy_rcu);
 }
 

net/ipv6/ip6_fib.c

@@ -162,7 +162,7 @@ struct fib6_info *fib6_info_alloc(gfp_t gfp_flags)
 	}
 
 	INIT_LIST_HEAD(&f6i->fib6_siblings);
-	atomic_set(&f6i->fib6_ref, 1);
+	refcount_set(&f6i->fib6_ref, 1);
 
 	return f6i;
 }
@@ -929,7 +929,7 @@ static void fib6_purge_rt(struct fib6_info *rt, struct fib6_node *fn,
 {
 	struct fib6_table *table = rt->fib6_table;
 
-	if (atomic_read(&rt->fib6_ref) != 1) {
+	if (refcount_read(&rt->fib6_ref) != 1) {
 		/* This route is used as dummy address holder in some split
 		 * nodes. It is not leaked, but it still holds other resources,
 		 * which must be released in time. So, scan ascendant nodes
@@ -2311,7 +2311,7 @@ static int ipv6_route_seq_show(struct seq_file *seq, void *v)
 
 	dev = rt->fib6_nh.fib_nh_dev;
 	seq_printf(seq, " %08x %08x %08x %08x %8s\n",
-		   rt->fib6_metric, atomic_read(&rt->fib6_ref), 0,
+		   rt->fib6_metric, refcount_read(&rt->fib6_ref), 0,
 		   flags, dev ? dev->name : "");
 	iter->w.leaf = NULL;
 	return 0;

net/ipv6/route.c

@@ -296,7 +296,7 @@ static const struct fib6_info fib6_null_entry_template = {
 	.fib6_flags	= (RTF_REJECT | RTF_NONEXTHOP),
 	.fib6_protocol  = RTPROT_KERNEL,
 	.fib6_metric	= ~(u32)0,
-	.fib6_ref	= ATOMIC_INIT(1),
+	.fib6_ref	= REFCOUNT_INIT(1),
 	.fib6_type	= RTN_UNREACHABLE,
 	.fib6_metrics	= (struct dst_metrics *)&dst_default_metrics,
 };