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    Subject[PATCH 3.12 107/133] tcp: metrics: Avoid duplicate entries with the same destination-IP
    Date
    3.12-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    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);




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