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[patch]: Introduce sysctl param
arp_evict_no_carrier (sonic-net#293)
This PR is to backport the following commits to kernel v5.10: torvalds/linux@fcdb44d The commit above is to introduce a new sysctl parameter `arp_evict_no_carrier`. Signed-off-by: Longxiang Lyu <lolv@microsoft.com> Signed-off-by: Longxiang Lyu <lolv@microsoft.com>
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patch/0001-net-arp-introduce-arp_evict_nocarrier-sysctl-paramet.patch
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| From fcdb44d08a95003c3d040aecdee286156ec6f34e Mon Sep 17 00:00:00 2001 | ||
| From: James Prestwood <prestwoj@gmail.com> | ||
| Date: Mon, 1 Nov 2021 10:36:28 -0700 | ||
| Subject: [PATCH] net: arp: introduce arp_evict_nocarrier sysctl parameter | ||
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| This change introduces a new sysctl parameter, arp_evict_nocarrier. | ||
| When set (default) the ARP cache will be cleared on a NOCARRIER event. | ||
| This new option has been defaulted to '1' which maintains existing | ||
| behavior. | ||
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| Clearing the ARP cache on NOCARRIER is relatively new, introduced by: | ||
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| commit 859bd2ef1fc1110a8031b967ee656c53a6260a76 | ||
| Author: David Ahern <dsahern@gmail.com> | ||
| Date: Thu Oct 11 20:33:49 2018 -0700 | ||
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| net: Evict neighbor entries on carrier down | ||
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| The reason for this changes is to prevent the ARP cache from being | ||
| cleared when a wireless device roams. Specifically for wireless roams | ||
| the ARP cache should not be cleared because the underlying network has not | ||
| changed. Clearing the ARP cache in this case can introduce significant | ||
| delays sending out packets after a roam. | ||
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| A user reported such a situation here: | ||
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| https://lore.kernel.org/linux-wireless/CACsRnHWa47zpx3D1oDq9JYnZWniS8yBwW1h0WAVZ6vrbwL_S0w@mail.gmail.com/ | ||
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| After some investigation it was found that the kernel was holding onto | ||
| packets until ARP finished which resulted in this 1 second delay. It | ||
| was also found that the first ARP who-has was never responded to, | ||
| which is actually what caues the delay. This change is more or less | ||
| working around this behavior, but again, there is no reason to clear | ||
| the cache on a roam anyways. | ||
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| As for the unanswered who-has, we know the packet made it OTA since | ||
| it was seen while monitoring. Why it never received a response is | ||
| unknown. In any case, since this is a problem on the AP side of things | ||
| all that can be done is to work around it until it is solved. | ||
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| Some background on testing/reproducing the packet delay: | ||
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| Hardware: | ||
| - 2 access points configured for Fast BSS Transition (Though I don't | ||
| see why regular reassociation wouldn't have the same behavior) | ||
| - Wireless station running IWD as supplicant | ||
| - A device on network able to respond to pings (I used one of the APs) | ||
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| Procedure: | ||
| - Connect to first AP | ||
| - Ping once to establish an ARP entry | ||
| - Start a tcpdump | ||
| - Roam to second AP | ||
| - Wait for operstate UP event, and note the timestamp | ||
| - Start pinging | ||
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| Results: | ||
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| Below is the tcpdump after UP. It was recorded the interface went UP at | ||
| 10:42:01.432875. | ||
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| 10:42:01.461871 ARP, Request who-has 192.168.254.1 tell 192.168.254.71, length 28 | ||
| 10:42:02.497976 ARP, Request who-has 192.168.254.1 tell 192.168.254.71, length 28 | ||
| 10:42:02.507162 ARP, Reply 192.168.254.1 is-at ac:86:74:55:b0:20, length 46 | ||
| 10:42:02.507185 IP 192.168.254.71 > 192.168.254.1: ICMP echo request, id 52792, seq 1, length 64 | ||
| 10:42:02.507205 IP 192.168.254.71 > 192.168.254.1: ICMP echo request, id 52792, seq 2, length 64 | ||
| 10:42:02.507212 IP 192.168.254.71 > 192.168.254.1: ICMP echo request, id 52792, seq 3, length 64 | ||
| 10:42:02.507219 IP 192.168.254.71 > 192.168.254.1: ICMP echo request, id 52792, seq 4, length 64 | ||
| 10:42:02.507225 IP 192.168.254.71 > 192.168.254.1: ICMP echo request, id 52792, seq 5, length 64 | ||
| 10:42:02.507232 IP 192.168.254.71 > 192.168.254.1: ICMP echo request, id 52792, seq 6, length 64 | ||
| 10:42:02.515373 IP 192.168.254.1 > 192.168.254.71: ICMP echo reply, id 52792, seq 1, length 64 | ||
| 10:42:02.521399 IP 192.168.254.1 > 192.168.254.71: ICMP echo reply, id 52792, seq 2, length 64 | ||
| 10:42:02.521612 IP 192.168.254.1 > 192.168.254.71: ICMP echo reply, id 52792, seq 3, length 64 | ||
| 10:42:02.521941 IP 192.168.254.1 > 192.168.254.71: ICMP echo reply, id 52792, seq 4, length 64 | ||
| 10:42:02.522419 IP 192.168.254.1 > 192.168.254.71: ICMP echo reply, id 52792, seq 5, length 64 | ||
| 10:42:02.523085 IP 192.168.254.1 > 192.168.254.71: ICMP echo reply, id 52792, seq 6, length 64 | ||
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| You can see the first ARP who-has went out very quickly after UP, but | ||
| was never responded to. Nearly a second later the kernel retries and | ||
| gets a response. Only then do the ping packets go out. If an ARP entry | ||
| is manually added prior to UP (after the cache is cleared) it is seen | ||
| that the first ping is never responded to, so its not only an issue with | ||
| ARP but with data packets in general. | ||
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| As mentioned prior, the wireless interface was also monitored to verify | ||
| the ping/ARP packet made it OTA which was observed to be true. | ||
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| Signed-off-by: James Prestwood <prestwoj@gmail.com> | ||
| Reviewed-by: David Ahern <dsahern@kernel.org> | ||
| Signed-off-by: Jakub Kicinski <kuba@kernel.org> | ||
| --- | ||
| Documentation/networking/ip-sysctl.rst | 9 +++++++++ | ||
| include/linux/inetdevice.h | 2 ++ | ||
| include/uapi/linux/ip.h | 1 + | ||
| include/uapi/linux/sysctl.h | 1 + | ||
| net/ipv4/arp.c | 11 ++++++++++- | ||
| net/ipv4/devinet.c | 4 ++++ | ||
| 6 files changed, 27 insertions(+), 1 deletion(-) | ||
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| diff --git a/Documentation/networking/ip-sysctl.rst b/Documentation/networking/ip-sysctl.rst | ||
| index 16b8bf72feaf..18fde4ed7a5e 100644 | ||
| --- a/Documentation/networking/ip-sysctl.rst | ||
| +++ b/Documentation/networking/ip-sysctl.rst | ||
| @@ -1611,6 +1611,15 @@ arp_accept - BOOLEAN | ||
| gratuitous arp frame, the arp table will be updated regardless | ||
| if this setting is on or off. | ||
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| +arp_evict_nocarrier - BOOLEAN | ||
| + Clears the ARP cache on NOCARRIER events. This option is important for | ||
| + wireless devices where the ARP cache should not be cleared when roaming | ||
| + between access points on the same network. In most cases this should | ||
| + remain as the default (1). | ||
| + | ||
| + - 1 - (default): Clear the ARP cache on NOCARRIER events | ||
| + - 0 - Do not clear ARP cache on NOCARRIER events | ||
| + | ||
| mcast_solicit - INTEGER | ||
| The maximum number of multicast probes in INCOMPLETE state, | ||
| when the associated hardware address is unknown. Defaults | ||
| diff --git a/include/linux/inetdevice.h b/include/linux/inetdevice.h | ||
| index a038feb63f23..518b484a7f07 100644 | ||
| --- a/include/linux/inetdevice.h | ||
| +++ b/include/linux/inetdevice.h | ||
| @@ -133,6 +133,8 @@ static inline void ipv4_devconf_setall(struct in_device *in_dev) | ||
| #define IN_DEV_ARP_ANNOUNCE(in_dev) IN_DEV_MAXCONF((in_dev), ARP_ANNOUNCE) | ||
| #define IN_DEV_ARP_IGNORE(in_dev) IN_DEV_MAXCONF((in_dev), ARP_IGNORE) | ||
| #define IN_DEV_ARP_NOTIFY(in_dev) IN_DEV_MAXCONF((in_dev), ARP_NOTIFY) | ||
| +#define IN_DEV_ARP_EVICT_NOCARRIER(in_dev) IN_DEV_ANDCONF((in_dev), \ | ||
| + ARP_EVICT_NOCARRIER) | ||
|
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||
| struct in_ifaddr { | ||
| struct hlist_node hash; | ||
| diff --git a/include/uapi/linux/ip.h b/include/uapi/linux/ip.h | ||
| index e42d13b55cf3..e00bbb9c47bb 100644 | ||
| --- a/include/uapi/linux/ip.h | ||
| +++ b/include/uapi/linux/ip.h | ||
| @@ -169,6 +169,7 @@ enum | ||
| IPV4_DEVCONF_DROP_UNICAST_IN_L2_MULTICAST, | ||
| IPV4_DEVCONF_DROP_GRATUITOUS_ARP, | ||
| IPV4_DEVCONF_BC_FORWARDING, | ||
| + IPV4_DEVCONF_ARP_EVICT_NOCARRIER, | ||
| __IPV4_DEVCONF_MAX | ||
| }; | ||
|
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||
| diff --git a/include/uapi/linux/sysctl.h b/include/uapi/linux/sysctl.h | ||
| index 1e05d3caa712..6a3b194c50fe 100644 | ||
| --- a/include/uapi/linux/sysctl.h | ||
| +++ b/include/uapi/linux/sysctl.h | ||
| @@ -482,6 +482,7 @@ enum | ||
| NET_IPV4_CONF_PROMOTE_SECONDARIES=20, | ||
| NET_IPV4_CONF_ARP_ACCEPT=21, | ||
| NET_IPV4_CONF_ARP_NOTIFY=22, | ||
| + NET_IPV4_CONF_ARP_EVICT_NOCARRIER=23, | ||
| }; | ||
|
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||
| /* /proc/sys/net/ipv4/netfilter */ | ||
| diff --git a/net/ipv4/arp.c b/net/ipv4/arp.c | ||
| index 922dd73e5740..857a144b1ea9 100644 | ||
| --- a/net/ipv4/arp.c | ||
| +++ b/net/ipv4/arp.c | ||
| @@ -1247,6 +1247,8 @@ static int arp_netdev_event(struct notifier_block *this, unsigned long event, | ||
| { | ||
| struct net_device *dev = netdev_notifier_info_to_dev(ptr); | ||
| struct netdev_notifier_change_info *change_info; | ||
| + struct in_device *in_dev; | ||
| + bool evict_nocarrier; | ||
|
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||
| switch (event) { | ||
| case NETDEV_CHANGEADDR: | ||
| @@ -1257,7 +1259,14 @@ static int arp_netdev_event(struct notifier_block *this, unsigned long event, | ||
| change_info = ptr; | ||
| if (change_info->flags_changed & IFF_NOARP) | ||
| neigh_changeaddr(&arp_tbl, dev); | ||
| - if (!netif_carrier_ok(dev)) | ||
| + | ||
| + in_dev = __in_dev_get_rtnl(dev); | ||
| + if (!in_dev) | ||
| + evict_nocarrier = true; | ||
| + else | ||
| + evict_nocarrier = IN_DEV_ARP_EVICT_NOCARRIER(in_dev); | ||
| + | ||
| + if (evict_nocarrier && !netif_carrier_ok(dev)) | ||
| neigh_carrier_down(&arp_tbl, dev); | ||
| break; | ||
| default: | ||
| diff --git a/net/ipv4/devinet.c b/net/ipv4/devinet.c | ||
| index f4468980b675..ec73a0d52d3e 100644 | ||
| --- a/net/ipv4/devinet.c | ||
| +++ b/net/ipv4/devinet.c | ||
| @@ -75,6 +75,7 @@ static struct ipv4_devconf ipv4_devconf = { | ||
| [IPV4_DEVCONF_SHARED_MEDIA - 1] = 1, | ||
| [IPV4_DEVCONF_IGMPV2_UNSOLICITED_REPORT_INTERVAL - 1] = 10000 /*ms*/, | ||
| [IPV4_DEVCONF_IGMPV3_UNSOLICITED_REPORT_INTERVAL - 1] = 1000 /*ms*/, | ||
| + [IPV4_DEVCONF_ARP_EVICT_NOCARRIER - 1] = 1, | ||
| }, | ||
| }; | ||
|
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| @@ -87,6 +88,7 @@ static struct ipv4_devconf ipv4_devconf_dflt = { | ||
| [IPV4_DEVCONF_ACCEPT_SOURCE_ROUTE - 1] = 1, | ||
| [IPV4_DEVCONF_IGMPV2_UNSOLICITED_REPORT_INTERVAL - 1] = 10000 /*ms*/, | ||
| [IPV4_DEVCONF_IGMPV3_UNSOLICITED_REPORT_INTERVAL - 1] = 1000 /*ms*/, | ||
| + [IPV4_DEVCONF_ARP_EVICT_NOCARRIER - 1] = 1, | ||
| }, | ||
| }; | ||
|
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| @@ -2532,6 +2534,8 @@ static struct devinet_sysctl_table { | ||
| DEVINET_SYSCTL_RW_ENTRY(ARP_IGNORE, "arp_ignore"), | ||
| DEVINET_SYSCTL_RW_ENTRY(ARP_ACCEPT, "arp_accept"), | ||
| DEVINET_SYSCTL_RW_ENTRY(ARP_NOTIFY, "arp_notify"), | ||
| + DEVINET_SYSCTL_RW_ENTRY(ARP_EVICT_NOCARRIER, | ||
| + "arp_evict_nocarrier"), | ||
| DEVINET_SYSCTL_RW_ENTRY(PROXY_ARP_PVLAN, "proxy_arp_pvlan"), | ||
| DEVINET_SYSCTL_RW_ENTRY(FORCE_IGMP_VERSION, | ||
| "force_igmp_version"), | ||
| -- | ||
| 2.17.1 | ||
|
|
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