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Commit 77f99ad1 authored by Christoph Paasch's avatar Christoph Paasch Committed by David S. Miller
Browse files

tcp: metrics: Avoid duplicate entries with the same destination-IP 



Because the tcp-metrics is an RCU-list, it may be that two
soft-interrupts are inside __tcp_get_metrics() for the same
destination-IP at the same time. If this destination-IP is not yet part of
the tcp-metrics, both soft-interrupts will end up in tcpm_new and create
a new entry for this IP.
So, we will have two tcp-metrics with the same destination-IP in the list.

This patch checks twice __tcp_get_metrics(). First without holding the
lock, then while holding the lock. The second one is there to confirm
that the entry has not been added by another soft-irq while waiting for
the spin-lock.

Fixes: 51c5d0c4 (tcp: Maintain dynamic metrics in local cache.)
Signed-off-by: default avatarChristoph Paasch <christoph.paasch@uclouvain.be>
Reviewed-by: default avatarEric Dumazet <edumazet@google.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent c196403b

net/ipv4/tcp_metrics.c

+32 −19
Original line number Diff line number Diff line
@@ -22,6 +22,9 @@ 


int sysctl_tcp_nometrics_save __read_mostly;



static struct tcp_metrics_block *__tcp_get_metrics(const struct inetpeer_addr *addr,

						   struct net *net, unsigned int hash);



struct tcp_fastopen_metrics {

	u16	mss;

	u16	syn_loss:10;		/* Recurring Fast Open SYN losses */
@@ -130,16 +133,41 @@ static void tcpm_suck_dst(struct tcp_metrics_block *tm, struct dst_entry *dst, 
	}

}



#define TCP_METRICS_TIMEOUT		(60 * 60 * HZ)



static void tcpm_check_stamp(struct tcp_metrics_block *tm, struct dst_entry *dst)

{

	if (tm && unlikely(time_after(jiffies, tm->tcpm_stamp + TCP_METRICS_TIMEOUT)))

		tcpm_suck_dst(tm, dst, false);

}



#define TCP_METRICS_RECLAIM_DEPTH	5

#define TCP_METRICS_RECLAIM_PTR		(struct tcp_metrics_block *) 0x1UL



static struct tcp_metrics_block *tcpm_new(struct dst_entry *dst,

					  struct inetpeer_addr *addr,

					  unsigned int hash,

					  bool reclaim)

					  unsigned int hash)

{

	struct tcp_metrics_block *tm;

	struct net *net;

	bool reclaim = false;



	spin_lock_bh(&tcp_metrics_lock);

	net = dev_net(dst->dev);



	/* While waiting for the spin-lock the cache might have been populated

	 * with this entry and so we have to check again.

	 */

	tm = __tcp_get_metrics(addr, net, hash);

	if (tm == TCP_METRICS_RECLAIM_PTR) {

		reclaim = true;

		tm = NULL;

	}

	if (tm) {

		tcpm_check_stamp(tm, dst);

		goto out_unlock;

	}



	if (unlikely(reclaim)) {

		struct tcp_metrics_block *oldest;
@@ -169,17 +197,6 @@ static struct tcp_metrics_block *tcpm_new(struct dst_entry *dst, 
	return tm;

}



#define TCP_METRICS_TIMEOUT		(60 * 60 * HZ)



static void tcpm_check_stamp(struct tcp_metrics_block *tm, struct dst_entry *dst)

{

	if (tm && unlikely(time_after(jiffies, tm->tcpm_stamp + TCP_METRICS_TIMEOUT)))

		tcpm_suck_dst(tm, dst, false);

}



#define TCP_METRICS_RECLAIM_DEPTH	5

#define TCP_METRICS_RECLAIM_PTR		(struct tcp_metrics_block *) 0x1UL



static struct tcp_metrics_block *tcp_get_encode(struct tcp_metrics_block *tm, int depth)

{

	if (tm)
@@ -282,7 +299,6 @@ static struct tcp_metrics_block *tcp_get_metrics(struct sock *sk, 
	struct inetpeer_addr addr;

	unsigned int hash;

	struct net *net;

	bool reclaim;



	addr.family = sk->sk_family;

	switch (addr.family) {
@@ -304,13 +320,10 @@ static struct tcp_metrics_block *tcp_get_metrics(struct sock *sk, 
	hash = hash_32(hash, net->ipv4.tcp_metrics_hash_log);



	tm = __tcp_get_metrics(&addr, net, hash);

	reclaim = false;

	if (tm == TCP_METRICS_RECLAIM_PTR) {

		reclaim = true;

	if (tm == TCP_METRICS_RECLAIM_PTR)

		tm = NULL;

	}

	if (!tm && create)

		tm = tcpm_new(dst, &addr, hash, reclaim);

		tm = tcpm_new(dst, &addr, hash);

	else

		tcpm_check_stamp(tm, dst);