net/ipv4: Use proper RCU APIs for writer-side in udp_offload.c

RCU writer side should use rcu_dereference_protected() and not
rcu_dereference(), fix that. This also removes the "suspicious RCU usage"
warning seen when running with CONFIG_PROVE_RCU.

Also, don't use rcu_assign_pointer/rcu_dereference for pointers
which are invisible beyond the udp offload code.

Fixes: b582ef0 ('net: Add GRO support for UDP encapsulating protocols')
Reported-by: Eric Dumazet <edumazet@google.com>
Cc: Eric Dumazet <edumazet@google.com>
Signed-off-by: Or Gerlitz <ogerlitz@mellanox.com>
Signed-off-by: Shlomo Pongratz <shlomop@mellanox.com>
Acked-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 8 insertions, 7 deletions

diff --git a/net/ipv4/udp_offload.c b/net/ipv4/udp_offload.c
index 2ffea6f31efc..88b4023ecfcf 100644
--- a/net/ipv4/udp_offload.c
+++ b/net/ipv4/udp_offload.c
@@ -17,6 +17,8 @@
 static DEFINE_SPINLOCK(udp_offload_lock);
 static struct udp_offload_priv __rcu *udp_offload_base __read_mostly;
 
+#define udp_deref_protected(X) rcu_dereference_protected(X, lockdep_is_held(&udp_offload_lock))
+
 struct udp_offload_priv {
         struct udp_offload      *offload;
         struct rcu_head         rcu;
@@ -100,7 +102,6 @@ out:
 
 int udp_add_offload(struct udp_offload *uo)
 {
-        struct udp_offload_priv __rcu **head = &udp_offload_base;
         struct udp_offload_priv *new_offload = kzalloc(sizeof(*new_offload), GFP_ATOMIC);
 
         if (!new_offload)
@@ -109,8 +110,8 @@ int udp_add_offload(struct udp_offload *uo)
         new_offload->offload = uo;
 
         spin_lock(&udp_offload_lock);
-        rcu_assign_pointer(new_offload->next, rcu_dereference(*head));
-        rcu_assign_pointer(*head, new_offload);
+        new_offload->next = udp_offload_base;
+        rcu_assign_pointer(udp_offload_base, new_offload);
         spin_unlock(&udp_offload_lock);
 
         return 0;
@@ -130,12 +131,12 @@ void udp_del_offload(struct udp_offload *uo)
 
         spin_lock(&udp_offload_lock);
 
-        uo_priv = rcu_dereference(*head);
+        uo_priv = udp_deref_protected(*head);
         for (; uo_priv != NULL;
-                uo_priv = rcu_dereference(*head)) {
-
+             uo_priv = udp_deref_protected(*head)) {
                 if (uo_priv->offload == uo) {
-                        rcu_assign_pointer(*head, rcu_dereference(uo_priv->next));
+                        rcu_assign_pointer(*head,
+                                           udp_deref_protected(uo_priv->next));
                         goto unlock;
                 }
                 head = &uo_priv->next;