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Commit 404e0a8b authored by Eric Dumazet's avatar Eric Dumazet Committed by David S. Miller
Browse files

net: ipv4: fix RCU races on dst refcounts 



commit c6cffba4 (ipv4: Fix input route performance regression.)
added various fatal races with dst refcounts.

crashes happen on tcp workloads if routes are added/deleted at the same
time.

The dst_free() calls from free_fib_info_rcu() are clearly racy.

We need instead regular dst refcounting (dst_release()) and make
sure dst_release() is aware of RCU grace periods :

Add DST_RCU_FREE flag so that dst_release() respects an RCU grace period
before dst destruction for cached dst

Introduce a new inet_sk_rx_dst_set() helper, using atomic_inc_not_zero()
to make sure we dont increase a zero refcount (On a dst currently
waiting an rcu grace period before destruction)

rt_cache_route() must take a reference on the new cached route, and
release it if was not able to install it.

With this patch, my machines survive various benchmarks.

Signed-off-by: default avatarEric Dumazet <edumazet@google.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent cca32e4b

include/net/dst.h

+1 −6
Original line number Diff line number Diff line
@@ -61,6 +61,7 @@ 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;
@@ -382,12 +383,6 @@ 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;

include/net/inet_sock.h

+13 −0
Original line number Diff line number Diff line
@@ -249,4 +249,17 @@ static inline __u8 inet_sk_flowi_flags(const struct sock *sk) 
	return flags;

}



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;

	}

}



#endif	/* _INET_SOCK_H */

net/core/dst.c

+21 −5
Original line number Diff line number Diff line
@@ -258,6 +258,15 @@ struct dst_entry *dst_destroy(struct dst_entry * dst) 
}

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) {
@@ -265,13 +274,17 @@ void dst_release(struct dst_entry *dst) 


		newrefcnt = atomic_dec_return(&dst->__refcnt);

		WARN_ON(newrefcnt < 0);

		if (unlikely(dst->flags & DST_NOCACHE) && !newrefcnt) {

		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);

			}

		}

	}

}

EXPORT_SYMBOL(dst_release);



u32 *dst_cow_metrics_generic(struct dst_entry *dst, unsigned long old)
@@ -320,11 +333,14 @@ 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

	 */

	if (unlikely(dst->flags & DST_NOCACHE)) {

	hold = (dst->flags & (DST_NOCACHE | DST_RCU_FREE)) == DST_NOCACHE;

	if (unlikely(hold)) {

		dst_hold(dst);

		skb_dst_set(skb, dst);

	} else {

net/decnet/dn_route.c

+6 −0
Original line number Diff line number Diff line
@@ -184,6 +184,12 @@ 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);

net/ipv4/fib_semantics.c

+2 −2
Original line number Diff line number Diff line
@@ -172,9 +172,9 @@ static void free_fib_info_rcu(struct rcu_head *head) 
		if (nexthop_nh->nh_exceptions)

			free_nh_exceptions(nexthop_nh);

		if (nexthop_nh->nh_rth_output)

			dst_free(&nexthop_nh->nh_rth_output->dst);

			dst_release(&nexthop_nh->nh_rth_output->dst);

		if (nexthop_nh->nh_rth_input)

			dst_free(&nexthop_nh->nh_rth_input->dst);

			dst_release(&nexthop_nh->nh_rth_input->dst);

	} endfor_nexthops(fi);



	release_net(fi->fib_net);