When the last packet of data to be transmitted on a call is queued, tx_top
is set and then the RXRPC_CALL_TX_LAST flag is set.  Unfortunately, this
leaves a race in the ACK processing side of things because the flag affects
the interpretation of tx_top and also allows us to start receiving reply
data before we've finished transmitting.

To fix this, make the following changes:

 (1) rxrpc_queue_packet() now sets a marker in the annotation buffer
     instead of setting the RXRPC_CALL_TX_LAST flag.

 (2) rxrpc_rotate_tx_window() detects the marker and sets the flag in the
     same context as the routines that use it.

 (3) rxrpc_end_tx_phase() is simplified to just shift the call state.
     The Tx window must have been rotated before calling to discard the
     last packet.

 (4) rxrpc_receiving_reply() is added to handle the arrival of the first
     DATA packet of a reply to a client call (which is an implicit ACK of
     the Tx phase).

 (5) The last part of rxrpc_input_ack() is reordered to perform Tx
     rotation, then soft-ACK application and then to end the phase if we've
     rotated the last packet.  In the event of a terminal ACK, the soft-ACK
     application will be skipped as nAcks should be 0.

 (6) rxrpc_input_ackall() now has to rotate as well as ending the phase.

In addition:

 (7) Alter the transmit tracepoint to log the rotation of the last packet.

 (8) Remove the no-longer relevant queue_reqack tracepoint note.  The
     ACK-REQUESTED packet header flag is now set as needed when we actually
     transmit the packet and may vary by retransmission.
Signed-off-by: David Howells <dhowells@redhat.com>

Fix the call timer in the following ways:

 (1) If call->resend_at or call->ack_at are before or equal to the current
     time, then ignore that timeout.

 (2) If call->expire_at is before or equal to the current time, then don't
     set the timer at all (possibly we should queue the call).

 (3) Don't skip modifying the timer if timer_pending() is true.  This
     indicates that the timer is working, not that it has expired and is
     running/waiting to run its expiry handler.

Also call rxrpc_set_timer() to start the call timer going rather than
calling add_timer().
Signed-off-by: David Howells <dhowells@redhat.com>

When rxrpc_input_soft_acks() is parsing the soft-ACKs from an ACK packet,
it updates the Tx packet annotations in the annotation buffer.  If a
soft-ACK is an ACK, then we overwrite unack'd, nak'd or to-be-retransmitted
states and that is fine; but if the soft-ACK is an NACK, we overwrite the
to-be-retransmitted with a nak - which isn't.

Instead, we need to let any scheduled retransmission stand if the packet
was NAK'd.

Note that we don't reissue a resend if the annotation is in the
to-be-retransmitted state because someone else must've scheduled the
resend already.
Signed-off-by: David Howells <dhowells@redhat.com>

When a DATA packet has its initial transmission, we may need to start or
adjust the resend timer.  Without this we end up relying on being sent a
NACK to initiate the resend.
Signed-off-by: David Howells <dhowells@redhat.com>

before_eq() and friends should be used to compare serial numbers (when not
checking for (non)equality) rather than casting to int, subtracting and
checking the result.
Signed-off-by: David Howells <dhowells@redhat.com>

ktime_add_ms() should be used to add the resend time (in ms) rather than
ktime_add_ns().
Signed-off-by: David Howells <dhowells@redhat.com>

Make sure that sendmsg() gets woken up if the call it is waiting for
completes abnormally.
Signed-off-by: David Howells <dhowells@redhat.com>

Don't send an IDLE ACK at the end of the transmission of the response to a
service call.  The service end resends DATA packets until the client sends an
ACK that hard-acks all the send data.  At that point, the call is complete.
Signed-off-by: David Howells <dhowells@redhat.com>

Set the timestamp on sk_buffs holding packets to be transmitted before
queueing them because the moment the packet is on the queue it can be seen
by the retransmission algorithm - which may see a completely random
timestamp.

If the retransmission algorithm sees such a timestamp, it may retransmit
the packet and, in future, tell the congestion management algorithm that
the retransmit timer expired.
Signed-off-by: David Howells <dhowells@redhat.com>

Change predecrement compare to post decrement compare to avoid an
unsigned integer wrap-around comparison when decrementing idx in
the while loop.

For example, when idx is zero, the current situation will
predecrement idx in the while loop, wrapping idx to the maximum
signed integer and cause out of bounds reads on rxq_info->msix_tbl[idx].
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Saeed Mahameed says:

====================
Mellanox 100G SRIOV offloads vlan push/pop

From Or Gerlitz:

This series further enhances the SRIOV TC offloads of mlx5 to handle
the TC vlan push and pop actions. This serves a common use-case in
virtualization systems where the virtual switch add (push) vlan tags
to packets sent from VMs and removes (pop) vlan tags before the packet
is received by the VM. We use the new E-Switch switchdev mode and the
TC vlan action to achieve that also in SW defined SRIOV environments by
offloading TC rules that contain this action along with forwarding
(TC mirred/redirect action) the packet.

In the first patch we add some helpers to access the TC vlan action info
by offloading drivers. The next five patches don't add any new functionality,
they do some refactoring and cleanups in the current code to be used next.

The seventh patch deals with supporting vlans by the mlx5 e-switch in switchdev
mode. The eighth patch does the vlan action offload from TC and the last patch
adds matching for vlans as typically required by TC flows that involve vlan
pop action.

The series was applied on top of commit 524605e5 "cxgb4: Convert to use simple_open()"
====================
Signed-off-by: David S. Miller <davem@davemloft.net>

Enhance the parsing of offloaded TC rules matches to handle vlans.
Signed-off-by: Or Gerlitz <ogerlitz@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Parse TC vlan actions and set the required elements to allow offloading.
Signed-off-by: Or Gerlitz <ogerlitz@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Many virtualization systems use a policy under which a vlan tag is
pushed to packets sent by guests, and popped before the packet is
forwarded to the VM.

The current generation of the mlx5 HW doesn't fully support that on
a per flow level. As such, we are addressing the above common use
case with the SRIOV e-Switch abilities to push vlan into packets
sent by VFs and pop vlan from packets forwarded to VFs.

The HW can match on the correct vlan being present in packets
forwarded to VFs (eSwitch steering is done before stripping
the tag), so this part is offloaded as is.

A common practice for vlans is to avoid both push vlan and pop vlan
for inter-host VM/VM (east-west) communication because in this case,
push on egress cancels out with pop on ingress.

For supporting that, we use a global eswitch vlan pop policy, hence
allowing guest A to communicate with both remote VM B and local VM C.
This works since the HW pops the vlan only if it exists (e.g for
C --> A packets but not for B --> A packets).

On the slow path, when a VF vport has an offloaded flow which involves
pushing vlans, wheres another flow is not currently offloaded, the
packets from the 2nd flow seen by the VF representor on the host have
vlan. The VF rep driver removes such vlan before calling into the host
networking stack.
Signed-off-by: Or Gerlitz <ogerlitz@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Factor the relevant code into a static inline helper (skb_from_cqe)
doing that.

Move the call to napi_gro_receive to be carried out just
after mlx5e_complete_rx_cqe returns.

Both changes are to be used for the VF representor as well
in the next commit.

This patch doesn't change any functionality.
Signed-off-by: Or Gerlitz <ogerlitz@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Put the representors related to the source and dest vports and the
action in struct mlx5_esw_flow_attr which is used while setting the FDB rule.

This patch doesn't change any functionality.
Signed-off-by: Or Gerlitz <ogerlitz@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

The HW can be programmed to push vlan, pop vlan or both.

A factorization step towards using the push/pop capabilties in the
eswitch offloads mode. This patch doesn't add new functionality.
Signed-off-by: Or Gerlitz <ogerlitz@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

The structure we use for the eswitch vport representor (mlx5_eswitch_rep)
has some fields which are set from upper layers in the driver when they
register the rep. Use explicit setting on registration time for them and
avoid global memcpy. This patch doesn't add new functionality.
Signed-off-by: Or Gerlitz <ogerlitz@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Set the vport value in the PF entry to be that of the uplink so
we can use it blindly over the tc / eswitch offload code without
translating it each time we deal with the uplink representor.
Signed-off-by: Or Gerlitz <ogerlitz@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Needed e.g for offloading drivers to pick the relevant attributes.
Signed-off-by: Or Gerlitz <ogerlitz@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

It looks like the following patch can make FQ very precise, even in VM
or stressed hosts. It matters at high pacing rates.

We take into account the difference between the time that was programmed
when last packet was sent, and current time (a drift of tens of usecs is
often observed)

Add an EWMA of the unthrottle latency to help diagnostics.

This latency is the difference between current time and oldest packet in
delayed RB-tree. This accounts for the high resolution timer latency,
but can be different under stress, as fq_check_throttled() can be
opportunistically be called from a dequeue() called after an enqueue()
for a different flow.

Tested:
// Start a 10Gbit flow
$ netperf --google-pacing-rate 1250000000 -H lpaa24 -l 10000 -- -K bbr &

Before patch :
$ sar -n DEV 10 5 | grep eth0 | grep Average
Average:         eth0  17106.04 756876.84   1102.75 1119049.02      0.00      0.00      0.52

After patch :
$ sar -n DEV 10 5 | grep eth0 | grep Average
Average:         eth0  17867.00 800245.90   1151.77 1183172.12      0.00      0.00      0.52

A new iproute2 tc can output the 'unthrottle latency' :

$ tc -s qd sh dev eth0 | grep latency
  0 gc, 0 highprio, 32490767 throttled, 2382 ns latency
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Add a NULL check before calling asynchronous MCDI completion functions
during device removal.

Fixes: 7014d7f6 ("sfc: allow asynchronous MCDI without completion function")
Signed-off-by: Bert Kenward <bkenward@solarflare.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Marcelo Ricardo Leitner says:

====================
sctp: fix the handling of SACK Gap Ack blocks

sctp_acked() is using 32bit arithmetics on 16bits vars, via TSN_lte()
macros, which is weird and confusing.

Once the offset to ctsn is calculated, all wrapping is already handled
and thus to verify the Gap Ack blocks we can just use pure
less/big-or-equal than checks.

Also, rename gap variable to tsn_offset, so it's more meaningful, as
it doesn't point to any gap at all.

Even so, I don't think this discrepancy resulted in any practical bug.

This patch is a preparation for the next one, which will introduce
typecheck() for TSN_lte() macros and would cause a compile error here.
Suggested-by: David Laight <David.Laight@ACULAB.COM>
Reported-by: David Laight <David.Laight@ACULAB.COM>
Signed-off-by: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>
====================
Signed-off-by: David S. Miller <davem@davemloft.net>

Make it similar to time_before() macros:
- easier to understand
- make use of typecheck() to avoid working on unexpected variable types
  (made the issue on previous patch visible)
- for _[lg]te versions, slighly faster, as the compiler used to generate
  a sequence of cmp/je/cmp/js instructions and now it's sub/test/jle
  (for _lte):

Before, for sctp_outq_sack:
	if (primary->cacc.changeover_active) {
    1f01:	80 b9 84 02 00 00 00 	cmpb   $0x0,0x284(%rcx)
    1f08:	74 6e                	je     1f78 <sctp_outq_sack+0xe8>
		u8 clear_cycling = 0;

		if (TSN_lte(primary->cacc.next_tsn_at_change, sack_ctsn)) {
    1f0a:	8b 81 80 02 00 00    	mov    0x280(%rcx),%eax
	return ((s) - (t)) & TSN_SIGN_BIT;
}

static inline int TSN_lte(__u32 s, __u32 t)
{
	return ((s) == (t)) || (((s) - (t)) & TSN_SIGN_BIT);
    1f10:	8b 7d bc             	mov    -0x44(%rbp),%edi
    1f13:	39 c7                	cmp    %eax,%edi
    1f15:	74 25                	je     1f3c <sctp_outq_sack+0xac>
    1f17:	39 f8                	cmp    %edi,%eax
    1f19:	78 21                	js     1f3c <sctp_outq_sack+0xac>
			primary->cacc.changeover_active = 0;

After:
	if (primary->cacc.changeover_active) {
    1ee7:	80 b9 84 02 00 00 00 	cmpb   $0x0,0x284(%rcx)
    1eee:	74 73                	je     1f63 <sctp_outq_sack+0xf3>
		u8 clear_cycling = 0;

		if (TSN_lte(primary->cacc.next_tsn_at_change, sack_ctsn)) {
    1ef0:	8b 81 80 02 00 00    	mov    0x280(%rcx),%eax
    1ef6:	2b 45 b4             	sub    -0x4c(%rbp),%eax
    1ef9:	85 c0                	test   %eax,%eax
    1efb:	7e 26                	jle    1f23 <sctp_outq_sack+0xb3>
			primary->cacc.changeover_active = 0;

*_lt() generated pretty much the same code.
Tested with gcc (GCC) 6.1.1 20160621.

This patch also removes SSN_lte as it is not used and cleanups some
comments.
Signed-off-by: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

sctp_acked() is using 32bit arithmetics on 16bits vars, via TSN_lte()
macros, which is weird and confusing.

Once the offset to ctsn is calculated, all wrapping is already handled
and thus to verify the Gap Ack blocks we can just use pure
less/big-or-equal than checks.

Also, rename gap variable to tsn_offset, so it's more meaningful, as
it doesn't point to any gap at all.

Even so, I don't think this discrepancy resulted in any practical bug.

This patch is a preparation for the next one, which will introduce
typecheck() for TSN_lte() macros and would cause a compile error here.
Suggested-by: David Laight <David.Laight@ACULAB.COM>
Reported-by: David Laight <David.Laight@ACULAB.COM>
Signed-off-by: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

On error path in route4_change(), 'f' could be NULL,
so we should check NULL before calling tcf_exts_destroy().

Fixes: b9a24bb7 ("net_sched: properly handle failure case of tcf_exts_init()")
Reported-by: kbuild test robot <fengguang.wu@intel.com>
Cc: Jamal Hadi Salim <jhs@mojatatu.com>
Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
Acked-by: Jamal Hadi Salim <jhs@mojatatu.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Pull media fixes from Mauro Carvalho Chehab:

 - several fixes for new drivers added for Kernel 4.8 addition (cec
   core, pulse8 cec driver and Mediatek vcodec)

 - a regression fix for cx23885 and saa7134 drivers

 - an important fix for rcar-fcp, making rcar_fcp_enable() return 0 on
   success

* tag 'media/v4.8-7' of git://git.kernel.org/pub/scm/linux/kernel/git/mchehab/linux-media: (25 commits)
  [media] cx23885/saa7134: assign q->dev to the PCI device
  [media] rcar-fcp: Make sure rcar_fcp_enable() returns 0 on success
  [media] cec: fix ioctl return code when not registered
  [media] cec: don't Feature Abort broadcast msgs when unregistered
  [media] vcodec:mediatek: Refine VP8 encoder driver
  [media] vcodec:mediatek: Refine H264 encoder driver
  [media] vcodec:mediatek: change H264 profile default to profile high
  [media] vcodec:mediatek: Add timestamp and timecode copy for V4L2 Encoder
  [media] vcodec:mediatek: Fix visible_height larger than coded_height issue in s_fmt_out
  [media] vcodec:mediatek: Fix fops_vcodec_release flow for V4L2 Encoder
  [media] vcodec:mediatek:code refine for v4l2 Encoder driver
  [media] cec-funcs.h: add missing vendor-specific messages
  [media] cec-edid: check for IEEE identifier
  [media] pulse8-cec: fix error handling
  [media] pulse8-cec: set correct Signal Free Time
  [media] mtk-vcodec: add HAS_DMA dependency
  [media] cec: ignore messages when log_addr_mask == 0
  [media] cec: add item to TODO
  [media] cec: set unclaimed addresses to CEC_LOG_ADDR_INVALID
  [media] cec: add CEC_LOG_ADDRS_FL_ALLOW_UNREG_FALLBACK flag
  ...

Pull networking fixes from David Miller:
 "Mostly small bits scattered all over the place, which is usually how
  things go this late in the -rc series.

   1) Proper driver init device resets in bnx2, from Baoquan He.

   2) Fix accounting overflow in __tcp_retransmit_skb(),
      sk_forward_alloc, and ip_idents_reserve, from Eric Dumazet.

   3) Fix crash in bna driver ethtool stats handling, from Ivan Vecera.

   4) Missing check of skb_linearize() return value in mac80211, from
      Johannes Berg.

   5) Endianness fix in nf_table_trace dumps, from Liping Zhang.

   6) SSN comparison fix in SCTP, from Marcelo Ricardo Leitner.

   7) Update DSA and b44 MAINTAINERS entries.

   8) Make input path of vti6 driver work again, from Nicolas Dichtel.

   9) Off-by-one in mlx4, from Sebastian Ott.

  10) Fix fallback route lookup handling in ipv6, from Vincent Bernat.

  11) Fix stack corruption on probe in qed driver, from Yuval Mintz.

  12) PHY init fixes in r8152 from Hayes Wang.

  13) Missing SKB free in irda_accept error path, from Phil Turnbull"

* git://git.kernel.org/pub/scm/linux/kernel/git/davem/net: (61 commits)
  tcp: properly account Fast Open SYN-ACK retrans
  tcp: fix under-accounting retransmit SNMP counters
  MAINTAINERS: Update b44 maintainer.
  net: get rid of an signed integer overflow in ip_idents_reserve()
  net/mlx4_core: Fix to clean devlink resources
  net: can: ifi: Configure transmitter delay
  vti6: fix input path
  ipmr, ip6mr: return lastuse relative to now
  r8152: disable ALDPS and EEE before setting PHY
  r8152: remove r8153_enable_eee
  r8152: move PHY settings to hw_phy_cfg
  r8152: move enabling PHY
  r8152: move some functions
  cxgb4/cxgb4vf: Allocate more queues for 25G and 100G adapter
  qed: Fix stack corruption on probe
  MAINTAINERS: Add an entry for the core network DSA code
  net: ipv6: fallback to full lookup if table lookup is unsuitable
  net/mlx5: E-Switch, Handle mode change failures
  net/mlx5: E-Switch, Fix error flow in the SRIOV e-switch init code
  net/mlx5: Fix flow counter bulk command out mailbox allocation
  ...

Instead of open coding it use the threaded irq mechanism in
xen-netback.
Signed-off-by: Juergen Gross <jgross@suse.com>
Acked-by: Wei Liu <wei.liu2@citrix.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Potential dangerous invalid pointer might be accessed if
the error happens when couple phy_device to net_device so
cleanup the error path.
Signed-off-by: Sean Wang <sean.wang@mediatek.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1) use new api [get|set]_link_ksettings instead
of [get|set]_settings old ones.

2) dev->phydev is sure being ready before calling
these callbacks, so removing all the sanity check
if it is existing.
Signed-off-by: Sean Wang <sean.wang@mediatek.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

remove the unused variable for parsing PHY address
and the related logic for sanity test which would
be all already handled done when of_mdiobus_register
was called
Reported-by: Nelson Chang <nelson.chang@mediatek.com>
Signed-off-by: Sean Wang <sean.wang@mediatek.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

reuse phydev already in struct net_device instead of creating
another new one in private structure.
Signed-off-by: Sean Wang <sean.wang@mediatek.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Sean Wang says:

====================
mediatek: add support for RGMII on GMAC0 through TRGMII hardware module

By default, GMAC0 is connected to built-in switch called
MT7530 through the proprietary interface called Turbo RGMII
(TRGMII). TRGMII also supports well for RGMII as generic external
PHY uses but requires some slight changes to the setup of TRGMII
and doesn't have well support on current driver.

So this patchset
1) provides the slight changes of the setup for RGMII can work
   through TRGMII
2) adds additional setting "trgmii" as PHY_INTERFACE_MODE_TRGMII
   about phy-mode on device tree to make GMAC0 distinguish which
   mode it runs
3) changes dynamically source clock, TX/RX delay and interface
   mode on TRGMII for adapting various link

Changes since v1:
- fixed the style of comment which doesn't have a space at
   the beginning and end of comment lines
- add support for phy-mode "trgmii" as PHY_INTERFACE_MODE_TRGMII
   into linux/phy.h
- enhance the Documentation about device tree binding for trgmii
  which is applicable only for GMAC0 which uses fixed-link
====================
Signed-off-by: David S. Miller <davem@davemloft.net>

Add the dts property for the capability if TRGMII supported on GAMC0
Signed-off-by: Sean Wang <sean.wang@mediatek.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Changing dynamically source clock, TX/RX delay and interface mode
used by TRGMII hardware module inside PHY capability polling routine
for adapting to the various speed of RGMII used by external PHY for
GMAC0.
Signed-off-by: Sean Wang <sean.wang@mediatek.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

adds PHY-mode "trgmii" as an extension for the operation
mode of the PHY interface for PHY_INTERFACE_MODE_TRGMII.
and adds a variable trgmii inside mtk_mac as the indication
to make the difference between the MAC connected to internal
switch or connected to external PHY by the given configuration
on the board and then to perform the corresponding setup on
TRGMII hardware module.
Signed-off-by: Sean Wang <sean.wang@mediatek.com>
Cc: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Merge tag 'rxrpc-rewrite-20160922-v2' of git://git.kernel.org/pub/scm/linux/kernel/git/dhowells/linux-fs

David Howells says:

====================
rxrpc: Preparation for slow-start algorithm [ver #2]

Here are some patches that prepare for improvements in ACK generation and
for the implementation of the slow-start part of the protocol:

 (1) Stop storing the protocol header in the Tx socket buffers, but rather
     generate it on the fly.  This potentially saves a little space and
     makes it easier to alter the header just before transmission (the
     flags may get altered and the serial number has to be changed).

 (2) Mask off the Tx buffer annotations and add a flag to record which ones
     have already been resent.

 (3) Track RTT on a per-peer basis for use in future changes.  Tracepoints
     are added to log this.

 (4) Send PING ACKs in response to incoming calls to elicit a PING-RESPONSE
     ACK from which RTT data can be calculated.  The response also carries
     other useful information.

 (5) Expedite PING-RESPONSE ACK generation from sendmsg.  If we're actively
     using sendmsg, this allows us, under some circumstances, to avoid
     having to rely on the background work item to run to generate this
     ACK.

     This requires ktime_sub_ms() to be added.

 (6) Set the REQUEST-ACK flag on some DATA packets to elicit ACK-REQUESTED
     ACKs from which RTT data can be calculated.

 (7) Limit the use of pings and ACK requests for RTT determination.

Changes:

 (V2) Don't use the C division operator for 64-bit division.  One instance
      should use do_div() and the other should be using nsecs_to_jiffies().

      The last two patches got transposed, leading to an undefined symbol
      in one of them.
Reported-by: kbuild test robot <lkp@intel.com>
====================
Signed-off-by: David S. Miller <davem@davemloft.net>

We don't want to send a PING ACK for every new incoming call as that just
adds to the network traffic.  Instead, we send a PING ACK to the first
three that we receive and then once per second thereafter.

This could probably be made adjustable in future.
Signed-off-by: David Howells <dhowells@redhat.com>