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Date: Sun, 25 Sep 2016 00:25:31 +0100 From: David Howells <dhowells@...hat.com> To: netdev@...r.kernel.org Cc: dhowells@...hat.com, linux-afs@...ts.infradead.org, linux-kernel@...r.kernel.org Subject: [PATCH net-next 5/8] rxrpc: Delay the resend timer to allow for nsec->jiffies conv error When determining the resend timer value, we have a value in nsec but the timer is in jiffies which may be a million or more times more coarse. nsecs_to_jiffies() rounds down - which means that the resend timeout expressed as jiffies is very likely earlier than the one expressed as nanoseconds from which it was derived. The problem is that rxrpc_resend() gets triggered by the timer, but can't then find anything to resend yet. It sets the timer again - but gets kicked off immediately again and again until the nanosecond-based expiry time is reached and we actually retransmit. Fix this by adding 1 to the jiffies-based resend_at value to counteract the rounding and make sure that the timer happens after the nanosecond-based expiry is passed. Alternatives would be to adjust the timestamp on the packets to align with the jiffie scale or to switch back to using jiffie-timestamps. Signed-off-by: David Howells <dhowells@...hat.com> --- net/rxrpc/call_event.c | 10 ++++++++-- 1 file changed, 8 insertions(+), 2 deletions(-) diff --git a/net/rxrpc/call_event.c b/net/rxrpc/call_event.c index a78a92fe5d77..d5bf9ce7ec6f 100644 --- a/net/rxrpc/call_event.c +++ b/net/rxrpc/call_event.c @@ -200,8 +200,14 @@ static void rxrpc_resend(struct rxrpc_call *call) ktime_to_ns(ktime_sub(skb->tstamp, max_age))); } - resend_at = ktime_sub(ktime_add_ms(oldest, rxrpc_resend_timeout), now); - call->resend_at = jiffies + nsecs_to_jiffies(ktime_to_ns(resend_at)); + resend_at = ktime_add_ms(oldest, rxrpc_resend_timeout); + call->resend_at = jiffies + + nsecs_to_jiffies(ktime_to_ns(ktime_sub(resend_at, now))) + + 1; /* We have to make sure that the calculated jiffies value + * falls at or after the nsec value, or we shall loop + * ceaselessly because the timer times out, but we haven't + * reached the nsec timeout yet. + */ /* Now go through the Tx window and perform the retransmissions. We * have to drop the lock for each send. If an ACK comes in whilst the
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