ccid2_hc_tx_rto_expire() timer callback always restarts the timer
again and can run indefinitely (unless it is stopped outside), and after
commit 120e9dabaf55 ("dccp: defer ccid_hc_tx_delete() at dismantle time"),
which moved ccid_hc_tx_delete() (also includes sk_stop_timer()) from
dccp_destroy_sock() to sk_destruct(), this started to happen quite often.
The timer prevents releasing the socket, as a result, sk_destruct() won't
be called.

Found with LTP/dccp_ipsec tests running on the bonding device,
which later couldn't be unloaded after the tests were completed:

  unregister_netdevice: waiting for bond0 to become free. Usage count = 148

Fixes: 2a91aa396739 ("[DCCP] CCID2: Initial CCID2 (TCP-Like) implementation")
Signed-off-by: Alexey Kodanev <alexey.koda...@oracle.com>
---

v2: * corrected bug origin commit id
    * clarified commit message about sk_stop_timer()

 net/dccp/ccids/ccid2.c |    3 +++
 1 files changed, 3 insertions(+), 0 deletions(-)

diff --git a/net/dccp/ccids/ccid2.c b/net/dccp/ccids/ccid2.c
index 1c75cd1..92d016e 100644
--- a/net/dccp/ccids/ccid2.c
+++ b/net/dccp/ccids/ccid2.c
@@ -140,6 +140,9 @@ static void ccid2_hc_tx_rto_expire(struct timer_list *t)
 
        ccid2_pr_debug("RTO_EXPIRE\n");
 
+       if (sk->sk_state == DCCP_CLOSED)
+               goto out;
+
        /* back-off timer */
        hc->tx_rto <<= 1;
        if (hc->tx_rto > DCCP_RTO_MAX)
-- 
1.7.1

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