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tcp: plug skb_still_in_host_queue() to TSQ 

Jakub and Neil reported an increase of RTO timers whenever
TX completions are delayed a bit more (by increasing
NIC TX coalescing parameters)

Main issue is that TCP stack has a logic preventing a packet
being retransmit if the prior clone has not yet been
orphaned or freed.

This logic came with commit 1f3279ae0c ("tcp: avoid
retransmits of TCP packets hanging in host queues")

Thankfully, in the case skb_still_in_host_queue() detects
the initial clone is still in flight, it can use TSQ logic
that will eventually retry later, at the moment the clone
is freed or orphaned.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: Neil Spring <ntspring@fb.com>
Reported-by: Jakub Kicinski <kuba@kernel.org>
Cc: Neal Cardwell <ncardwell@google.com>
Cc: Yuchung Cheng <ycheng@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Eric Dumazet 2021-03-11 12:35:04 -08:00 committed by David S. Miller
parent 8176f8c0f0
commit f4dae54e48
2 changed files with 9 additions and 5 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
include/linux/skbuff.h
View File

@ -1140,7 +1140,7 @@ static inline bool skb_fclone_busy(const struct sock *sk,
return skb->fclone == SKB_FCLONE_ORIG &&
refcount_read(&fclones->fclone_ref) > 1 &&
fclones->skb2.sk == sk;
READ_ONCE(fclones->skb2.sk) == sk;
}
/**

12
net/ipv4/tcp_output.c
View File

@ -2775,13 +2775,17 @@ bool tcp_schedule_loss_probe(struct sock *sk, bool advancing_rto)
* a packet is still in a qdisc or driver queue.
* In this case, there is very little point doing a retransmit !
*/
static bool skb_still_in_host_queue(const struct sock *sk,
static bool skb_still_in_host_queue(struct sock *sk,
const struct sk_buff *skb)
{
if (unlikely(skb_fclone_busy(sk, skb))) {
NET_INC_STATS(sock_net(sk),
LINUX_MIB_TCPSPURIOUS_RTX_HOSTQUEUES);
return true;
set_bit(TSQ_THROTTLED, &sk->sk_tsq_flags);
smp_mb__after_atomic();
if (skb_fclone_busy(sk, skb)) {
NET_INC_STATS(sock_net(sk),
LINUX_MIB_TCPSPURIOUS_RTX_HOSTQUEUES);
return true;
}
}
return false;
}