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Date: Tue, 9 Jul 2013 23:57:01 +0200
From: Hannes Frederic Sowa <hannes@...essinduktion.org>
To: nicolas.dichtel@...nd.com
Cc: netdev@...r.kernel.org, yoshfuji@...ux-ipv6.org,
petrus.lt@...il.com, davem@...emloft.net
Subject: Re: [PATCH RFC] ipv6: fix route selection if kernel is not compiled with CONFIG_IPV6_ROUTER_PREF
Hello Nicolas!
I am currently trying to fix the nexthop selection for kernels compiled
without support for CONFIG_IPV6_ROUTER_PREF. I attached my current patch
below. While testing I got the following kernel panic in ecmp code:
[ 80.144667] ------------[ cut here ]------------
[ 80.145172] kernel BUG at net/ipv6/ip6_fib.c:733!
[ 80.145172] invalid opcode: 0000 [#1] SMP
[ 80.145172] Modules linked in: 8021q nf_conntrack_netbios_ns nf_conntrack_broadcast ipt_MASQUERADE ip6table_mangle ip6t_REJECT nf_conntrack_ipv6 nf_defrag_ipv6 iptable_nat nf_nat_ipv4 nf_nat iptable_mangle nf_conntrack_ipv4 nf_defrag_ipv4 xt_conntrack nf_conntrack ebtable_filter ebtables ip6table_filter ip6_tables snd_hda_intel snd_hda_codec snd_hwdep snd_seq snd_seq_device snd_pcm snd_page_alloc snd_timer virtio_balloon snd soundcore i2c_piix4 i2c_core virtio_net virtio_blk
[ 80.145172] CPU: 1 PID: 786 Comm: ping6 Not tainted 3.10.0+ #118
[ 80.145172] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011
[ 80.145172] task: ffff880117fa0000 ti: ffff880118770000 task.ti: ffff880118770000
[ 80.145172] RIP: 0010:[<ffffffff815f3b5d>] [<ffffffff815f3b5d>] fib6_add+0x75d/0x830
[ 80.145172] RSP: 0018:ffff880118771798 EFLAGS: 00010202
[ 80.145172] RAX: 0000000000000000 RBX: 0000000000000000 RCX: ffff88011350e480
[ 80.145172] RDX: ffff88011350e238 RSI: 0000000000000004 RDI: ffff88011350f738
[ 80.145172] RBP: ffff880118771848 R08: ffff880117903280 R09: 0000000000000001
[ 80.145172] R10: 0000000000000000 R11: 0000000000000000 R12: ffff88011350f680
[ 80.145172] R13: ffff880117903280 R14: ffff880118771890 R15: ffff88011350ef90
[ 80.145172] FS: 00007f02b5127740(0000) GS:ffff88011fd00000(0000) knlGS:0000000000000000
[ 80.145172] CS: 0010 DS: 0000 ES: 0000 CR0: 000000008005003b
[ 80.145172] CR2: 00007f981322a000 CR3: 00000001181b1000 CR4: 00000000000006e0
[ 80.145172] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[ 80.145172] DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
[ 80.145172] Stack:
[ 80.145172] 0000000000000001 ffff880100000000 ffff880100000000 ffff880117903280
[ 80.145172] 0000000000000000 ffff880119a4cf00 0000000000000400 00000000000007fa
[ 80.145172] 0000000000000000 0000000000000000 0000000000000000 ffff88011350f680
[ 80.145172] Call Trace:
[ 80.145172] [<ffffffff815eeceb>] ? rt6_bind_peer+0x4b/0x90
[ 80.145172] [<ffffffff815ed985>] __ip6_ins_rt+0x45/0x70
[ 80.145172] [<ffffffff815eee35>] ip6_ins_rt+0x35/0x40
[ 80.145172] [<ffffffff815ef1e4>] ip6_pol_route.isra.44+0x3a4/0x4b0
[ 80.145172] [<ffffffff815ef34a>] ip6_pol_route_output+0x2a/0x30
[ 80.145172] [<ffffffff81616077>] fib6_rule_action+0xd7/0x210
[ 80.145172] [<ffffffff815ef320>] ? ip6_pol_route_input+0x30/0x30
[ 80.145172] [<ffffffff81553026>] fib_rules_lookup+0xc6/0x140
[ 80.145172] [<ffffffff81616374>] fib6_rule_lookup+0x44/0x80
[ 80.145172] [<ffffffff815ef320>] ? ip6_pol_route_input+0x30/0x30
[ 80.145172] [<ffffffff815edea3>] ip6_route_output+0x73/0xb0
[ 80.145172] [<ffffffff815dfdf3>] ip6_dst_lookup_tail+0x2c3/0x2e0
[ 80.145172] [<ffffffff813007b1>] ? list_del+0x11/0x40
[ 80.145172] [<ffffffff81082a4c>] ? remove_wait_queue+0x3c/0x50
[ 80.145172] [<ffffffff815dfe4d>] ip6_dst_lookup_flow+0x3d/0xa0
[ 80.145172] [<ffffffff815fda77>] rawv6_sendmsg+0x267/0xc20
[ 80.145172] [<ffffffff815a8a83>] inet_sendmsg+0x63/0xb0
[ 80.145172] [<ffffffff8128eb93>] ? selinux_socket_sendmsg+0x23/0x30
[ 80.145172] [<ffffffff815218d6>] sock_sendmsg+0xa6/0xd0
[ 80.145172] [<ffffffff81524a68>] SYSC_sendto+0x128/0x180
[ 80.145172] [<ffffffff8109825c>] ? update_curr+0xec/0x170
[ 80.145172] [<ffffffff81041d09>] ? kvm_clock_get_cycles+0x9/0x10
[ 80.145172] [<ffffffff810afd1e>] ? __getnstimeofday+0x3e/0xd0
[ 80.145172] [<ffffffff8152509e>] SyS_sendto+0xe/0x10
[ 80.145172] [<ffffffff8164efd9>] system_call_fastpath+0x16/0x1b
[ 80.145172] Code: fe ff ff 41 f6 45 2a 06 0f 85 ca fe ff ff 49 8b 7e 08 4c 89 ee e8 94 ef ff ff e9 b9 fe ff ff 48 8b 82 28 05 00 00 e9 01 ff ff ff <0f> 0b 49 8b 54 24 30 0d 00 00 40 00 89 83 14 01 00 00 48 89 53
[ 80.145172] RIP [<ffffffff815f3b5d>] fib6_add+0x75d/0x830
[ 80.145172] RSP <ffff880118771798>
[ 80.387413] ---[ end trace 02f20b7a8b81ed95 ]---
[ 80.390154] Kernel panic - not syncing: Fatal exception in interrupt
The relevant code is:
725 /* For each sibling in the list, increment the counter of
726 * siblings. BUG() if counters does not match, list of siblings
727 * is broken!
728 */
729 rt6i_nsiblings = 0;
730 list_for_each_entry_safe(sibling, temp_sibling,
731 &rt->rt6i_siblings, rt6i_siblings) {
732 sibling->rt6i_nsiblings++;
733 BUG_ON(sibling->rt6i_nsiblings != rt->rt6i_nsiblings);
734 rt6i_nsiblings++;
735 }
736 BUG_ON(rt6i_nsiblings != rt->rt6i_nsiblings);
737 }
Currently, I don't know if I my patch is to blame or something in the ecmp logic.
Another thing I just noticed is:
1240 /* Remove this entry from other siblings */
1241 if (rt->rt6i_nsiblings) {
1242 struct rt6_info *sibling, *next_sibling;
1243
1244 list_for_each_entry_safe(sibling, next_sibling,
1245 &rt->rt6i_siblings, rt6i_siblings)
1246 sibling->rt6i_nsiblings--;
1247 rt->rt6i_nsiblings = 0;
1248 list_del_init(&rt->rt6i_siblings);
1249 }
Are we sure we decrement all sibling's rt6i_nsiblings? Shouldn't we
start iterating from fn->leaf? But this does not seem to cause it,
because my trace does not report any calls to fib6_del_route.
You could try reproduce it by having an interface autoconfigured with
a default router with NUD_VALID neighbour. I then added an unused vlan
interface (vid 100 in my case) and added the following ip addresses:
ip -6 a a 2001:ffff::1/64 dev eth0.100
ip -6 r a 2000::/3 nexthop via 2001:ffff::30 nexthop via 2001:ffff::31 nexthop via 2001:ffff::32 nexthop via 2001:ffff::33
(all nexthops should not be reachable)
After starting a ping6 2000::1 the box should panic soon, after the
first nexthop entry times out.
Perhaps you could give me a hint?
Thanks a lot,
Hannes
[PATCH RFC] ipv6: fix route selection if kernel not compiled with CONFIG_IPV6_ROUTER_PREF
This is a follow-up patch to 3630d40067a21d4dfbadc6002bb469ce26ac5d52
("ipv6: rt6_check_neigh should successfully verify neigh if no NUD
information are available").
Since the removal of rt->n in rt6_info we can end up with a dst ==
NULL in rt6_check_neigh. In case the kernel is not compiled with
CONFIG_IPV6_ROUTER_PREF we should also select a route with unkown
NUD state but we must not avoid doing round robin selection on routes
with the same target. So introduce and pass down a boolean ``do_rr'' to
indicate when we should update rt->rr_ptr. As soon as no route is valid
we do backtracking and do a lookup on a higher level in the fib trie.
To hold correct state on the NUD selection we need to create a neighbour
entry as soon as we tried to validate a nexthop.
I changed the return value of rt6_check_neigh to:
1 in case of the dst entry validated
-1 in case of we had no dst_entry and we need to do rr now
-2 in case a we had a dst_entry and it did not validate
In case of CONFIG_IPV6_ROUTER_PREF, rt6_probe does not allocate an
neighbour entry (!CONFIG_IPV6_ROUTER_PREF: rt6_probe is a nop). Because
of this, we have to create a neighbour entry on nexthop validation to
track earlier validation errors. We recheck NUD state here to shortcurcuit
NUD_NOARP neighbours.
This seems to be the least complex fix for stable and net. I'll introduce
a new route lookup flag 'idempotent' as soon as next opens to not let
ip route get trigger active NUD validation if CONFIG_IPV6_ROUTER_PREF
is enabled. Currently we trigger active NUD validation if compiled with
CONFIG_IPV6_ROUTER_PREF.
It also seems advantageous to make CONFIG_IPV6_ROUTER_PREF a runtime
switch and just select the default operation on compile-time.
v2:
a) improved rt6_check_neigh logic and documented return values
Reported-by: Pierre Emeriaud <petrus.lt@...il.com>
Cc: YOSHIFUJI Hideaki <yoshfuji@...ux-ipv6.org>
---
net/ipv6/route.c | 62 +++++++++++++++++++++++++++++++++++---------------------
1 file changed, 39 insertions(+), 23 deletions(-)
diff --git a/net/ipv6/route.c b/net/ipv6/route.c
index bd5fd70..c5d9e68 100644
--- a/net/ipv6/route.c
+++ b/net/ipv6/route.c
@@ -531,28 +531,34 @@ static inline int rt6_check_dev(struct rt6_info *rt, int oif)
return 0;
}
-static inline bool rt6_check_neigh(struct rt6_info *rt)
+/* This function checks if a neighbour is reachable for routing
+ * purposes. It returns -2 in case the neighbour should not get
+ * selected as a viable router, -1 in case it should get selected with
+ * lowest score and afterwards trying roundrobin. 1 indicates a
+ * successfull verification.
+ */
+static inline int rt6_check_neigh(struct rt6_info *rt)
{
struct neighbour *neigh;
- bool ret = false;
+ int ret = -2;
if (rt->rt6i_flags & RTF_NONEXTHOP ||
!(rt->rt6i_flags & RTF_GATEWAY))
- return true;
+ return 1;
rcu_read_lock_bh();
neigh = __ipv6_neigh_lookup_noref(rt->dst.dev, &rt->rt6i_gateway);
if (neigh) {
read_lock(&neigh->lock);
if (neigh->nud_state & NUD_VALID)
- ret = true;
+ ret = 1;
#ifdef CONFIG_IPV6_ROUTER_PREF
else if (!(neigh->nud_state & NUD_FAILED))
- ret = true;
+ ret = 1;
#endif
read_unlock(&neigh->lock);
- } else if (IS_ENABLED(CONFIG_IPV6_ROUTER_PREF)) {
- ret = true;
+ } else {
+ ret = IS_ENABLED(CONFIG_IPV6_ROUTER_PREF) ? 1 : -1;
}
rcu_read_unlock_bh();
@@ -566,43 +572,52 @@ static int rt6_score_route(struct rt6_info *rt, int oif,
m = rt6_check_dev(rt, oif);
if (!m && (strict & RT6_LOOKUP_F_IFACE))
- return -1;
+ return -2;
#ifdef CONFIG_IPV6_ROUTER_PREF
m |= IPV6_DECODE_PREF(IPV6_EXTRACT_PREF(rt->rt6i_flags)) << 2;
#endif
- if (!rt6_check_neigh(rt) && (strict & RT6_LOOKUP_F_REACHABLE))
- return -1;
+ if (strict & RT6_LOOKUP_F_REACHABLE) {
+ int n = rt6_check_neigh(rt);
+ if (n < 0)
+ return n;
+ }
return m;
}
static struct rt6_info *find_match(struct rt6_info *rt, int oif, int strict,
- int *mpri, struct rt6_info *match)
+ int *mpri, struct rt6_info *match,
+ bool *do_rr)
{
int m;
+ bool match_do_rr = false;
if (rt6_check_expired(rt))
goto out;
m = rt6_score_route(rt, oif, strict);
- if (m < 0)
+ if (m == -1 && !IS_ENABLED(CONFIG_IPV6_ROUTER_PREF)) {
+ match_do_rr = true;
+ m = 0; /* lowest valid score */
+ } else if (m < 0) {
goto out;
+ }
+
+ if (strict & RT6_LOOKUP_F_REACHABLE)
+ rt6_probe(rt);
if (m > *mpri) {
- if (strict & RT6_LOOKUP_F_REACHABLE)
- rt6_probe(match);
+ *do_rr = match_do_rr;
*mpri = m;
match = rt;
- } else if (strict & RT6_LOOKUP_F_REACHABLE) {
- rt6_probe(rt);
}
-
out:
return match;
}
static struct rt6_info *find_rr_leaf(struct fib6_node *fn,
struct rt6_info *rr_head,
- u32 metric, int oif, int strict)
+ u32 metric, int oif, int strict,
+ bool *do_rr)
{
struct rt6_info *rt, *match;
int mpri = -1;
@@ -610,10 +625,10 @@ static struct rt6_info *find_rr_leaf(struct fib6_node *fn,
match = NULL;
for (rt = rr_head; rt && rt->rt6i_metric == metric;
rt = rt->dst.rt6_next)
- match = find_match(rt, oif, strict, &mpri, match);
+ match = find_match(rt, oif, strict, &mpri, match, do_rr);
for (rt = fn->leaf; rt && rt != rr_head && rt->rt6i_metric == metric;
rt = rt->dst.rt6_next)
- match = find_match(rt, oif, strict, &mpri, match);
+ match = find_match(rt, oif, strict, &mpri, match, do_rr);
return match;
}
@@ -622,15 +637,16 @@ static struct rt6_info *rt6_select(struct fib6_node *fn, int oif, int strict)
{
struct rt6_info *match, *rt0;
struct net *net;
+ bool do_rr = false;
rt0 = fn->rr_ptr;
if (!rt0)
fn->rr_ptr = rt0 = fn->leaf;
- match = find_rr_leaf(fn, rt0, rt0->rt6i_metric, oif, strict);
+ match = find_rr_leaf(fn, rt0, rt0->rt6i_metric, oif, strict,
+ &do_rr);
- if (!match &&
- (strict & RT6_LOOKUP_F_REACHABLE)) {
+ if (do_rr) {
struct rt6_info *next = rt0->dst.rt6_next;
/* no entries matched; do round-robin */
--
1.8.1.4
--
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