path: root/net
diff options
authorJohn Ogness <john.ogness@linutronix.de>2014-02-09 18:40:11 -0800
committerDavid S. Miller <davem@davemloft.net>2014-02-10 15:23:39 -0800
commitbf06200e732de613a1277984bf34d1a21c2de03d (patch)
treea6526d9291de28a71ffdf85940968399d0c4768d /net
parent684bd2e199c82e00e96e123a5baa581a0f2b4872 (diff)
tcp: tsq: fix nonagle handling
Commit 46d3ceabd8d9 ("tcp: TCP Small Queues") introduced a possible regression for applications using TCP_NODELAY. If TCP session is throttled because of tsq, we should consult tp->nonagle when TX completion is done and allow us to send additional segment, especially if this segment is not a full MSS. Otherwise this segment is sent after an RTO. [edumazet] : Cooked the changelog, added another fix about testing sk_wmem_alloc twice because TX completion can happen right before setting TSQ_THROTTLED bit. This problem is particularly visible with recent auto corking, but might also be triggered with low tcp_limit_output_bytes values or NIC drivers delaying TX completion by hundred of usec, and very low rtt. Thomas Glanzmann for example reported an iscsi regression, caused by tcp auto corking making this bug quite visible. Fixes: 46d3ceabd8d9 ("tcp: TCP Small Queues") Signed-off-by: John Ogness <john.ogness@linutronix.de> Signed-off-by: Eric Dumazet <edumazet@google.com> Reported-by: Thomas Glanzmann <thomas@glanzmann.de> Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'net')
1 files changed, 11 insertions, 2 deletions
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index 10435b3b9d0f..3be16727f058 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -698,7 +698,8 @@ static void tcp_tsq_handler(struct sock *sk)
if ((1 << sk->sk_state) &
- tcp_write_xmit(sk, tcp_current_mss(sk), 0, 0, GFP_ATOMIC);
+ tcp_write_xmit(sk, tcp_current_mss(sk), tcp_sk(sk)->nonagle,
* One tasklet per cpu tries to send more skbs.
@@ -1904,7 +1905,15 @@ static bool tcp_write_xmit(struct sock *sk, unsigned int mss_now, int nonagle,
if (atomic_read(&sk->sk_wmem_alloc) > limit) {
set_bit(TSQ_THROTTLED, &tp->tsq_flags);
- break;
+ /* It is possible TX completion already happened
+ * before we set TSQ_THROTTLED, so we must
+ * test again the condition.
+ * We abuse smp_mb__after_clear_bit() because
+ * there is no smp_mb__after_set_bit() yet
+ */
+ smp_mb__after_clear_bit();
+ if (atomic_read(&sk->sk_wmem_alloc) > limit)
+ break;
limit = mss_now;

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