[PATCH v3 net 5/5] ipv6: Replace spinlock with seqlock and rcu in ip6_tunnel

Martin KaFai Lau
2015-09-11T18:07:34Z

This patch uses a seqlock to ensure consistency between idst->dst and
idst->cookie. It also makes dst freeing from fib tree to undergo a
rcu grace period.

Signed-off-by: Martin KaFai Lau <kafai@fb.com>
---
include/net/ip6_tunnel.h | 4 ++--
net/ipv6/ip6_fib.c | 9 +++++++--
net/ipv6/ip6_tunnel.c | 51 +++++++++++++++++++++++++-----------------------
3 files changed, 36 insertions(+), 28 deletions(-)

diff --git a/include/net/ip6_tunnel.h b/include/net/ip6_tunnel.h
index 60b4f40..65c2a93 100644
--- a/include/net/ip6_tunnel.h
+++ b/include/net/ip6_tunnel.h
@@ -33,8 +33,8 @@ struct __ip6_tnl_parm {
};

struct ip6_tnl_dst {
- spinlock_t lock;
- struct dst_entry *dst;
+ seqlock_t lock;
+ struct dst_entry __rcu *dst;
u32 cookie;
};

diff --git a/net/ipv6/ip6_fib.c b/net/ipv6/ip6_fib.c
index e68350b..8a9ec01 100644
--- a/net/ipv6/ip6_fib.c
+++ b/net/ipv6/ip6_fib.c
@@ -155,6 +155,11 @@ static void node_free(struct fib6_node *fn)
kmem_cache_free(fib6_node_kmem, fn);
}

+static void rt6_rcu_free(struct rt6_info *rt)
+{
+ call_rcu(&rt->dst.rcu_head, dst_rcu_free);
+}
+
static void rt6_free_pcpu(struct rt6_info *non_pcpu_rt)
{
int cpu;
@@ -169,7 +174,7 @@ static void rt6_free_pcpu(struct rt6_info *non_pcpu_rt)
ppcpu_rt = per_cpu_ptr(non_pcpu_rt->rt6i_pcpu, cpu);
pcpu_rt = *ppcpu_rt;
if (pcpu_rt) {
- dst_free(&pcpu_rt->dst);
+ rt6_rcu_free(pcpu_rt);
*ppcpu_rt = NULL;
}
}
@@ -181,7 +186,7 @@ static void rt6_release(struct rt6_info *rt)
{
if (atomic_dec_and_test(&rt->rt6i_ref)) {
rt6_free_pcpu(rt);
- dst_free(&rt->dst);
+ rt6_rcu_free(rt);
}
}

diff --git a/net/ipv6/ip6_tunnel.c b/net/ipv6/ip6_tunnel.c
index 851cf6d..d27312a 100644
--- a/net/ipv6/ip6_tunnel.c
+++ b/net/ipv6/ip6_tunnel.c
@@ -126,45 +126,48 @@ static struct net_device_stats *ip6_get_stats(struct net_device *dev)
* Locking : hash tables are protected by RCU and RTNL
*/

-static void __ip6_tnl_per_cpu_dst_set(struct ip6_tnl_dst *idst,
- struct dst_entry *dst)
+static void ip6_tnl_per_cpu_dst_set(struct ip6_tnl_dst *idst,
+ struct dst_entry *dst)
{
- dst_release(idst->dst);
+ write_seqlock_bh(&idst->lock);
+ dst_release(rcu_dereference_protected(
+ idst->dst,
+ lockdep_is_held(&idst->lock->lock)));
if (dst) {
dst_hold(dst);
idst->cookie = rt6_get_cookie((struct rt6_info *)dst);
} else {
idst->cookie = 0;
}
- idst->dst = dst;
-}
-
-static void ip6_tnl_per_cpu_dst_set(struct ip6_tnl_dst *idst,
- struct dst_entry *dst)
-{
-
- spin_lock_bh(&idst->lock);
- __ip6_tnl_per_cpu_dst_set(idst, dst);
- spin_unlock_bh(&idst->lock);
+ rcu_assign_pointer(idst->dst, dst);
+ write_sequnlock_bh(&idst->lock);
}

struct dst_entry *ip6_tnl_dst_get(struct ip6_tnl *t)
{
struct ip6_tnl_dst *idst;
struct dst_entry *dst;
+ unsigned int seq;
+ u32 cookie;

idst = raw_cpu_ptr(t->dst_cache);
- spin_lock_bh(&idst->lock);
- dst = idst->dst;
- if (dst) {
- if (!dst->obsolete || dst->ops->check(dst, idst->cookie)) {
- dst_hold(idst->dst);
- } else {
- __ip6_tnl_per_cpu_dst_set(idst, NULL);
- dst = NULL;
- }
+
+ rcu_read_lock();
+ do {
+ seq = read_seqbegin(&idst->lock);
+ dst = rcu_dereference(idst->dst);
+ cookie = idst->cookie;
+ } while (read_seqretry(&idst->lock, seq));
+
+ if (dst && !atomic_inc_not_zero(&dst->__refcnt))
+ dst = NULL;
+ rcu_read_unlock();
+
+ if (dst && dst->obsolete && !dst->ops->check(dst, cookie)) {
+ ip6_tnl_per_cpu_dst_set(idst, NULL);
+ dst_release(dst);
+ dst = NULL;
}
- spin_unlock_bh(&idst->lock);
return dst;
}
EXPORT_SYMBOL_GPL(ip6_tnl_dst_get);
@@ -204,7 +207,7 @@ int ip6_tnl_dst_init(struct ip6_tnl *t)
return -ENOMEM;

for_each_possible_cpu(i)
- spin_lock_init(&per_cpu_ptr(t->dst_cache, i)->lock);
+ seqlock_init(&per_cpu_ptr(t->dst_cache, i)->lock);

return 0;
}
--
2.5.1