[PATCH 03/17] xfrm: state: use atomic_inc_not_zero to increment refcount

[Steffen Klassert]

From: Florian Westphal <f...@strlen.de>

Once xfrm_state_lookup_byaddr no longer acquires the state lock another
cpu might be freeing the state entry at the same time.

To detect this we use atomic_inc_not_zero, we then signal -EAGAIN to
caller in case our result was stale.

Signed-off-by: Florian Westphal <f...@strlen.de>
Signed-off-by: Steffen Klassert <steffen.klass...@secunet.com>
---
 net/xfrm/xfrm_state.c | 21 ++++++++++++++++-----
 1 file changed, 16 insertions(+), 5 deletions(-)

diff --git a/net/xfrm/xfrm_state.c b/net/xfrm/xfrm_state.c
index 904ab4d..84c1db6 100644
--- a/net/xfrm/xfrm_state.c
+++ b/net/xfrm/xfrm_state.c
@@ -37,6 +37,11 @@
 
 static unsigned int xfrm_state_hashmax __read_mostly = 1 * 1024 * 1024;
 
+static inline bool xfrm_state_hold_rcu(struct xfrm_state __rcu *x)
+{
+       return atomic_inc_not_zero(&x->refcnt);
+}
+
 static inline unsigned int xfrm_dst_hash(struct net *net,
                                         const xfrm_address_t *daddr,
                                         const xfrm_address_t *saddr,
@@ -668,7 +673,8 @@ static struct xfrm_state *__xfrm_state_lookup(struct net 
*net, u32 mark,
 
                if ((mark & x->mark.m) != x->mark.v)
                        continue;
-               xfrm_state_hold(x);
+               if (!xfrm_state_hold_rcu(x))
+                       continue;
                return x;
        }
 
@@ -692,7 +698,8 @@ static struct xfrm_state *__xfrm_state_lookup_byaddr(struct 
net *net, u32 mark,
 
                if ((mark & x->mark.m) != x->mark.v)
                        continue;
-               xfrm_state_hold(x);
+               if (!xfrm_state_hold_rcu(x))
+                       continue;
                return x;
        }
 
@@ -871,10 +878,14 @@ found:
                }
        }
 out:
-       if (x)
-               xfrm_state_hold(x);
-       else
+       if (x) {
+               if (!xfrm_state_hold_rcu(x)) {
+                       *err = -EAGAIN;
+                       x = NULL;
+               }
+       } else {
                *err = acquire_in_progress ? -EAGAIN : error;
+       }
        spin_unlock_bh(&net->xfrm.xfrm_state_lock);
        if (to_put)
                xfrm_state_put(to_put);
-- 
1.9.1