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Date: Wed, 11 Mar 2015 22:01:13 +0100
From: Ulf Samuelsson <netdev@...gii.com>
To: netdev@...r.kernel.org
Subject: [PATCH] neighbour.c: Avoid GC directly after state change
The neighbour state is changed in the ARP timer handler.
If the state is changed to NUD_STALE, then the neighbour
entry becomes a candidate for garbage collection.
The garbage collection is handled by a "periodic work" routine.
When :
* noone refers to the entry
* the state is no longer valid (I.E: NUD_STALE).
* the timeout value has been reached or state is FAILED
the "periodic work" routine will notify
the stack that the entry should be deleted.
A user application monitoring and controlling the neighbour table
using NETLINK may fail, if the "period work" routine is run
directly after the state has been changed to NUD_STALE,
but before the user application has had a chance to change
the state to something valid.
The "period work" routine will detect the NUD_STALE state
and if the timeout value has been reached, it will notify the stack
that the entry should be deleted.
The patch adds a check in the periodic work routine
which will skip test for garbage collection
unless a number of ticks has passed since the last time
the neighbour entry state was changed.
The feature is controlled through Kconfig
The featuree is enabled by setting ARP_GC_APPLY_GUARDBAND
The guardband time (in ticks) is set in ARP_GC_GUARDBAND
Default time is 100 ms if HZ_### is set.
Signed-off-by: Ulf Samuelsson <netdev@...gii.com>
---
net/Kconfig | 32 ++++++++++++++++++++++++++++++++
net/core/neighbour.c | 15 ++++++++++++---
2 files changed, 44 insertions(+), 3 deletions(-)
diff --git a/net/Kconfig b/net/Kconfig
index 44dd578..099a5dd 100644
--- a/net/Kconfig
+++ b/net/Kconfig
@@ -77,6 +77,38 @@ config INET
Short answer: say Y.
if INET
+
+#
+# Core Network configuration
+#
+
+config ARP_GC_APPLY_GUARDBAND
+ bool "IP: ARP: Avoid garbage collection directly after state change"
+ default n
+ ---help---
+ With this item selected, an entry in the neighbour table
+ will not be garbage collected directly after the ARP state
+ has changed to STALE of FAILED
+ This allows an application program change the state to something valid
+ before garbage colllection occurs.
+
+ If unsure, say N.
+
+config ARP_GC_GUARDBAND
+ int "Guardband time on garbage collection"
+ depends on ARP_GC_APPLY_GUARDBAND
+ default 10 if HZ_100
+ default 25 if HZ_250
+ default 30 if HZ_300
+ default 100 if HZ_1000
+ default 100
+
+ ---help---
+ The number of ticks to delay garbage collection
+ after the neighbour entry has been updated
+ A delay of 100 ms is reasonable.
+ With CONFIG_HZ = 250, this value should be 25
+
source "net/ipv4/Kconfig"
source "net/ipv6/Kconfig"
source "net/netlabel/Kconfig"
diff --git a/net/core/neighbour.c b/net/core/neighbour.c
index 70fe9e1..194195d 100644
--- a/net/core/neighbour.c
+++ b/net/core/neighbour.c
@@ -786,13 +786,23 @@ static void neigh_periodic_work(struct work_struct *work)
state = n->nud_state;
if (state & (NUD_PERMANENT | NUD_IN_TIMER)) {
- write_unlock(&n->lock);
goto next_elt;
}
if (time_before(n->used, n->confirmed))
n->used = n->confirmed;
+#if defined(CONFIG_ARP_GC_APPLY_GUARDBAND)
+ /* Do not garbage collect directly after we
+ * updated n->state to allow applications to
+ * react to the event
+ */
+ if (time_before(jiffies,
+ n->updated + CONFIG_ARP_GC_GUARDBAND)) {
+ goto next_elt;
+ }
+#endif
+
if (atomic_read(&n->refcnt) == 1 &&
(state == NUD_FAILED ||
time_after(jiffies, n->used + NEIGH_VAR(n->parms, GC_STALETIME)))) {
@@ -802,9 +812,8 @@ static void neigh_periodic_work(struct work_struct *work)
neigh_cleanup_and_release(n);
continue;
}
- write_unlock(&n->lock);
-
next_elt:
+ write_unlock(&n->lock);
np = &n->next;
}
/*
--
1.7.9.5
--
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