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authorEric Dumazet <eric.dumazet@gmail.com>2012-07-31 01:08:23 +0000
committerDavid S. Miller <davem@davemloft.net>2012-07-31 14:41:38 -0700
commit54764bb647b2e847c512acf8d443df965da35000 (patch)
tree3918f6f42679d0ebdcef230f28285f99d178be62 /net
parent5a0d513b622ee41e117fc37e26e27e8ef42e8dae (diff)
downloadlinux-54764bb647b2e847c512acf8d443df965da35000.tar.gz
ipv4: Restore old dst_free() behavior.
commit 404e0a8b6a55 (net: ipv4: fix RCU races on dst refcounts) tried to solve a race but added a problem at device/fib dismantle time : We really want to call dst_free() as soon as possible, even if sockets still have dst in their cache. dst_release() calls in free_fib_info_rcu() are not welcomed. Root of the problem was that now we also cache output routes (in nh_rth_output), we must use call_rcu() instead of call_rcu_bh() in rt_free(), because output route lookups are done in process context. Based on feedback and initial patch from David Miller (adding another call_rcu_bh() call in fib, but it appears it was not the right fix) I left the inet_sk_rx_dst_set() helper and added __rcu attributes to nh_rth_output and nh_rth_input to better document what is going on in this code. Signed-off-by: Eric Dumazet <edumazet@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'net')
-rw-r--r--net/core/dst.c26
-rw-r--r--net/decnet/dn_route.c6
-rw-r--r--net/ipv4/fib_semantics.c21
-rw-r--r--net/ipv4/route.c26
4 files changed, 39 insertions, 40 deletions
diff --git a/net/core/dst.c b/net/core/dst.c
index d9e33ebe170..069d51d2941 100644
--- a/net/core/dst.c
+++ b/net/core/dst.c
@@ -258,15 +258,6 @@ again:
}
EXPORT_SYMBOL(dst_destroy);
-static void dst_rcu_destroy(struct rcu_head *head)
-{
- struct dst_entry *dst = container_of(head, struct dst_entry, rcu_head);
-
- dst = dst_destroy(dst);
- if (dst)
- __dst_free(dst);
-}
-
void dst_release(struct dst_entry *dst)
{
if (dst) {
@@ -274,14 +265,10 @@ void dst_release(struct dst_entry *dst)
newrefcnt = atomic_dec_return(&dst->__refcnt);
WARN_ON(newrefcnt < 0);
- if (unlikely(dst->flags & (DST_NOCACHE | DST_RCU_FREE)) && !newrefcnt) {
- if (dst->flags & DST_RCU_FREE) {
- call_rcu_bh(&dst->rcu_head, dst_rcu_destroy);
- } else {
- dst = dst_destroy(dst);
- if (dst)
- __dst_free(dst);
- }
+ if (unlikely(dst->flags & DST_NOCACHE) && !newrefcnt) {
+ dst = dst_destroy(dst);
+ if (dst)
+ __dst_free(dst);
}
}
}
@@ -333,14 +320,11 @@ EXPORT_SYMBOL(__dst_destroy_metrics_generic);
*/
void skb_dst_set_noref(struct sk_buff *skb, struct dst_entry *dst)
{
- bool hold;
-
WARN_ON(!rcu_read_lock_held() && !rcu_read_lock_bh_held());
/* If dst not in cache, we must take a reference, because
* dst_release() will destroy dst as soon as its refcount becomes zero
*/
- hold = (dst->flags & (DST_NOCACHE | DST_RCU_FREE)) == DST_NOCACHE;
- if (unlikely(hold)) {
+ if (unlikely(dst->flags & DST_NOCACHE)) {
dst_hold(dst);
skb_dst_set(skb, dst);
} else {
diff --git a/net/decnet/dn_route.c b/net/decnet/dn_route.c
index 26719779ad8..85a3604c87c 100644
--- a/net/decnet/dn_route.c
+++ b/net/decnet/dn_route.c
@@ -184,12 +184,6 @@ static __inline__ unsigned int dn_hash(__le16 src, __le16 dst)
return dn_rt_hash_mask & (unsigned int)tmp;
}
-static inline void dst_rcu_free(struct rcu_head *head)
-{
- struct dst_entry *dst = container_of(head, struct dst_entry, rcu_head);
- dst_free(dst);
-}
-
static inline void dnrt_free(struct dn_route *rt)
{
call_rcu_bh(&rt->dst.rcu_head, dst_rcu_free);
diff --git a/net/ipv4/fib_semantics.c b/net/ipv4/fib_semantics.c
index e55171f184f..625cf185c48 100644
--- a/net/ipv4/fib_semantics.c
+++ b/net/ipv4/fib_semantics.c
@@ -161,6 +161,21 @@ static void free_nh_exceptions(struct fib_nh *nh)
kfree(hash);
}
+static void rt_nexthop_free(struct rtable __rcu **rtp)
+{
+ struct rtable *rt = rcu_dereference_protected(*rtp, 1);
+
+ if (!rt)
+ return;
+
+ /* Not even needed : RCU_INIT_POINTER(*rtp, NULL);
+ * because we waited an RCU grace period before calling
+ * free_fib_info_rcu()
+ */
+
+ dst_free(&rt->dst);
+}
+
/* Release a nexthop info record */
static void free_fib_info_rcu(struct rcu_head *head)
{
@@ -171,10 +186,8 @@ static void free_fib_info_rcu(struct rcu_head *head)
dev_put(nexthop_nh->nh_dev);
if (nexthop_nh->nh_exceptions)
free_nh_exceptions(nexthop_nh);
- if (nexthop_nh->nh_rth_output)
- dst_release(&nexthop_nh->nh_rth_output->dst);
- if (nexthop_nh->nh_rth_input)
- dst_release(&nexthop_nh->nh_rth_input->dst);
+ rt_nexthop_free(&nexthop_nh->nh_rth_output);
+ rt_nexthop_free(&nexthop_nh->nh_rth_input);
} endfor_nexthops(fi);
release_net(fi->fib_net);
diff --git a/net/ipv4/route.c b/net/ipv4/route.c
index d6eabcfe8a9..2bd10747746 100644
--- a/net/ipv4/route.c
+++ b/net/ipv4/route.c
@@ -1199,23 +1199,31 @@ restart:
fnhe->fnhe_stamp = jiffies;
}
+static inline void rt_free(struct rtable *rt)
+{
+ call_rcu(&rt->dst.rcu_head, dst_rcu_free);
+}
+
static void rt_cache_route(struct fib_nh *nh, struct rtable *rt)
{
- struct rtable *orig, *prev, **p = &nh->nh_rth_output;
+ struct rtable *orig, *prev, **p = (struct rtable **)&nh->nh_rth_output;
if (rt_is_input_route(rt))
- p = &nh->nh_rth_input;
+ p = (struct rtable **)&nh->nh_rth_input;
orig = *p;
- rt->dst.flags |= DST_RCU_FREE;
- dst_hold(&rt->dst);
prev = cmpxchg(p, orig, rt);
if (prev == orig) {
if (orig)
- dst_release(&orig->dst);
+ rt_free(orig);
} else {
- dst_release(&rt->dst);
+ /* Routes we intend to cache in the FIB nexthop have
+ * the DST_NOCACHE bit clear. However, if we are
+ * unsuccessful at storing this route into the cache
+ * we really need to set it.
+ */
+ rt->dst.flags |= DST_NOCACHE;
}
}
@@ -1412,7 +1420,7 @@ static int __mkroute_input(struct sk_buff *skb,
do_cache = false;
if (res->fi) {
if (!itag) {
- rth = FIB_RES_NH(*res).nh_rth_input;
+ rth = rcu_dereference(FIB_RES_NH(*res).nh_rth_input);
if (rt_cache_valid(rth)) {
skb_dst_set_noref(skb, &rth->dst);
goto out;
@@ -1574,7 +1582,7 @@ local_input:
do_cache = false;
if (res.fi) {
if (!itag) {
- rth = FIB_RES_NH(res).nh_rth_input;
+ rth = rcu_dereference(FIB_RES_NH(res).nh_rth_input);
if (rt_cache_valid(rth)) {
skb_dst_set_noref(skb, &rth->dst);
err = 0;
@@ -1742,7 +1750,7 @@ static struct rtable *__mkroute_output(const struct fib_result *res,
if (fi) {
fnhe = find_exception(&FIB_RES_NH(*res), fl4->daddr);
if (!fnhe) {
- rth = FIB_RES_NH(*res).nh_rth_output;
+ rth = rcu_dereference(FIB_RES_NH(*res).nh_rth_output);
if (rt_cache_valid(rth)) {
dst_hold(&rth->dst);
return rth;