[PATCH 3.10 080/104] tcp: metrics: Avoid duplicate entries with the same destination-IP

Greg Kroah-Hartman
2014-02-04T22:42:31Z

From: Christoph Paasch <christoph.paasch@uclouvain.be>

[ Upstream commit 77f99ad16a07aa062c2d30fae57b1fee456f6ef6 ]

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: 51c5d0c4b169b (tcp: Maintain dynamic metrics in local cache.)
Signed-off-by: Christoph Paasch <christoph.paasch@uclouvain.be>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
net/ipv4/tcp_metrics.c | 51 ++++++++++++++++++++++++++++++-------------------
1 file changed, 32 insertions(+), 19 deletions(-)

--- a/net/ipv4/tcp_metrics.c
+++ b/net/ipv4/tcp_metrics.c
@@ -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_met
}
}

+#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 @@ out_unlock:
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)
@@ -280,7 +297,6 @@ static struct tcp_metrics_block *tcp_get
struct inetpeer_addr addr;
unsigned int hash;
struct net *net;
- bool reclaim;

addr.family = sk->sk_family;
switch (addr.family) {
@@ -300,13 +316,10 @@ static struct tcp_metrics_block *tcp_get
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);