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Date: Tue, 31 Jul 2012 13:08:23 +0200
From: Eric Dumazet <eric.dumazet@...il.com>
To: David Miller <davem@...emloft.net>
Cc: netdev@...r.kernel.org
Subject: [PATCH v2] ipv4: Restore old dst_free() behavior.
From: Eric Dumazet <edumazet@...gle.com>
On Mon, 2012-07-30 at 22:38 -0700, David Miller wrote:
> Eric, this is what I'd like to propose.
>
> It seems the problem you were likely running into was simply
> the fact that we were not inserting an RCU grace period for
> the dst_free() that we do when purging a FIB nexthop.
>
> So this reverts your change, and instead adds the necessary
> call_rcu_bh() wrapper around the dst_free() done in fib_semantics.c
>
> That makes it so that we don't need all of that inc_not_zero stuff for
> sockets, and the special dst flag. If we set the pointer to NULL,
> then do the dst_free() via RCU, we can test that refcount safely in
> dst_free() since it can only decrease at that point.
>
> What do you think? Does it pass your tests?
It doesnt.
But I believe I found why, thats the good news ;)
In the past, we used RCU only for input routes, thats why using
call_rcu_bh() was OK.
But now we alse cache output routes, we must use call_rcu(), because
on output path we use rcu_read_lock() 'only', in process context,
not from softirq handler.
If you dont mind, I would like to keep inet_sk_rx_dst_set() helper
because I believe its cleaner and I'll probably add IPv6 stuff on it
(the cookie thing)
Also I added __rcu attributes to nh_rth_output and nh_rth_input to
better document what is going on in this code.
Thanks
[PATCH v2] 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@...gle.com>
---
include/net/dst.h | 7 ++++++-
include/net/inet_sock.h | 10 +++-------
include/net/ip_fib.h | 4 ++--
net/core/dst.c | 26 +++++---------------------
net/decnet/dn_route.c | 6 ------
net/ipv4/fib_semantics.c | 21 +++++++++++++++++----
net/ipv4/route.c | 26 +++++++++++++++++---------
7 files changed, 50 insertions(+), 50 deletions(-)
diff --git a/include/net/dst.h b/include/net/dst.h
index 31a9fd3..baf5978 100644
--- a/include/net/dst.h
+++ b/include/net/dst.h
@@ -61,7 +61,6 @@ struct dst_entry {
#define DST_NOPEER 0x0040
#define DST_FAKE_RTABLE 0x0080
#define DST_XFRM_TUNNEL 0x0100
-#define DST_RCU_FREE 0x0200
unsigned short pending_confirm;
@@ -383,6 +382,12 @@ static inline void dst_free(struct dst_entry *dst)
__dst_free(dst);
}
+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 dst_confirm(struct dst_entry *dst)
{
dst->pending_confirm = 1;
diff --git a/include/net/inet_sock.h b/include/net/inet_sock.h
index e3fd34c..83b567f 100644
--- a/include/net/inet_sock.h
+++ b/include/net/inet_sock.h
@@ -253,13 +253,9 @@ static inline void inet_sk_rx_dst_set(struct sock *sk, const struct sk_buff *skb
{
struct dst_entry *dst = skb_dst(skb);
- if (atomic_inc_not_zero(&dst->__refcnt)) {
- if (!(dst->flags & DST_RCU_FREE))
- dst->flags |= DST_RCU_FREE;
-
- sk->sk_rx_dst = dst;
- inet_sk(sk)->rx_dst_ifindex = skb->skb_iif;
- }
+ dst_hold(dst);
+ sk->sk_rx_dst = dst;
+ inet_sk(sk)->rx_dst_ifindex = skb->skb_iif;
}
#endif /* _INET_SOCK_H */
diff --git a/include/net/ip_fib.h b/include/net/ip_fib.h
index e69c3a4..e521a03 100644
--- a/include/net/ip_fib.h
+++ b/include/net/ip_fib.h
@@ -81,8 +81,8 @@ struct fib_nh {
__be32 nh_gw;
__be32 nh_saddr;
int nh_saddr_genid;
- struct rtable *nh_rth_output;
- struct rtable *nh_rth_input;
+ struct rtable __rcu *nh_rth_output;
+ struct rtable __rcu *nh_rth_input;
struct fnhe_hash_bucket *nh_exceptions;
};
diff --git a/net/core/dst.c b/net/core/dst.c
index d9e33eb..069d51d 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 2671977..85a3604 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 e55171f..625cf18 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 d6eabcf..2bd1074 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;
--
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