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

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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: 51c5d0c4b1 (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>
This commit is contained in:
Christoph Paasch 2014-01-16 20:01:21 +01:00 committed by David S. Miller
parent c196403b79
commit 77f99ad16a
1 changed files with 32 additions and 19 deletions
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51
net/ipv4/tcp_metrics.c
View File

@ -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 @@ 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)
@ -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);