Commit 54764bb6 authored by Eric Dumazet's avatar Eric Dumazet Committed by David S. Miller

ipv4: Restore old dst_free() behavior.

commit 404e0a8b (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: default avatarEric Dumazet <edumazet@google.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 5a0d513b
......@@ -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;
......
......@@ -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 */
......@@ -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;
};
......
......@@ -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 {
......
......@@ -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);
......
......@@ -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);
......
......@@ -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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