This is a note to let you know that I've just added the patch titled net: ipv6: Do not duplicate DAD on link up to the 4.10-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: net-ipv6-do-not-duplicate-dad-on-link-up.patch and it can be found in the queue-4.10 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From foo@baz Thu May 11 10:37:58 CEST 2017 From: David Ahern <dsahern@xxxxxxxxx> Date: Tue, 2 May 2017 14:43:44 -0700 Subject: net: ipv6: Do not duplicate DAD on link up From: David Ahern <dsahern@xxxxxxxxx> [ Upstream commit 6d717134a1a6e1b34a7d0d70e953037bc2642046 ] Andrey reported a warning triggered by the rcu code: ------------[ cut here ]------------ WARNING: CPU: 1 PID: 5911 at lib/debugobjects.c:289 debug_print_object+0x175/0x210 ODEBUG: activate active (active state 1) object type: rcu_head hint: (null) Modules linked in: CPU: 1 PID: 5911 Comm: a.out Not tainted 4.11.0-rc8+ #271 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011 Call Trace: __dump_stack lib/dump_stack.c:16 dump_stack+0x192/0x22d lib/dump_stack.c:52 __warn+0x19f/0x1e0 kernel/panic.c:549 warn_slowpath_fmt+0xe0/0x120 kernel/panic.c:564 debug_print_object+0x175/0x210 lib/debugobjects.c:286 debug_object_activate+0x574/0x7e0 lib/debugobjects.c:442 debug_rcu_head_queue kernel/rcu/rcu.h:75 __call_rcu.constprop.76+0xff/0x9c0 kernel/rcu/tree.c:3229 call_rcu_sched+0x12/0x20 kernel/rcu/tree.c:3288 rt6_rcu_free net/ipv6/ip6_fib.c:158 rt6_release+0x1ea/0x290 net/ipv6/ip6_fib.c:188 fib6_del_route net/ipv6/ip6_fib.c:1461 fib6_del+0xa42/0xdc0 net/ipv6/ip6_fib.c:1500 __ip6_del_rt+0x100/0x160 net/ipv6/route.c:2174 ip6_del_rt+0x140/0x1b0 net/ipv6/route.c:2187 __ipv6_ifa_notify+0x269/0x780 net/ipv6/addrconf.c:5520 addrconf_ifdown+0xe60/0x1a20 net/ipv6/addrconf.c:3672 ... Andrey's reproducer program runs in a very tight loop, calling 'unshare -n' and then spawning 2 sets of 14 threads running random ioctl calls. The relevant networking sequence: 1. New network namespace created via unshare -n - ip6tnl0 device is created in down state 2. address added to ip6tnl0 - equivalent to ip -6 addr add dev ip6tnl0 fd00::bb/1 - DAD is started on the address and when it completes the host route is inserted into the FIB 3. ip6tnl0 is brought up - the new fixup_permanent_addr function restarts DAD on the address 4. exit namespace - teardown / cleanup sequence starts - once in a blue moon, lo teardown appears to happen BEFORE teardown of ip6tunl0 + down on 'lo' removes the host route from the FIB since the dst->dev for the route is loobback + host route added to rcu callback list * rcu callback has not run yet, so rt is NOT on the gc list so it has NOT been marked obsolete 5. in parallel to 4. worker_thread runs addrconf_dad_completed - DAD on the address on ip6tnl0 completes - calls ipv6_ifa_notify which inserts the host route All of that happens very quickly. The result is that a host route that has been deleted from the IPv6 FIB and added to the RCU list is re-inserted into the FIB. The exit namespace eventually gets to cleaning up ip6tnl0 which removes the host route from the FIB again, calls the rcu function for cleanup -- and triggers the double rcu trace. The root cause is duplicate DAD on the address -- steps 2 and 3. Arguably, DAD should not be started in step 2. The interface is in the down state, so it can not really send out requests for the address which makes starting DAD pointless. Since the second DAD was introduced by a recent change, seems appropriate to use it for the Fixes tag and have the fixup function only start DAD for addresses in the PREDAD state which occurs in addrconf_ifdown if the address is retained. Big thanks to Andrey for isolating a reliable reproducer for this problem. Fixes: f1705ec197e7 ("net: ipv6: Make address flushing on ifdown optional") Reported-by: Andrey Konovalov <andreyknvl@xxxxxxxxxx> Signed-off-by: David Ahern <dsahern@xxxxxxxxx> Tested-by: Andrey Konovalov <andreyknvl@xxxxxxxxxx> Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- net/ipv6/addrconf.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) --- a/net/ipv6/addrconf.c +++ b/net/ipv6/addrconf.c @@ -3288,7 +3288,8 @@ static int fixup_permanent_addr(struct i idev->dev, 0, 0); } - addrconf_dad_start(ifp); + if (ifp->state == INET6_IFADDR_STATE_PREDAD) + addrconf_dad_start(ifp); return 0; } @@ -3643,7 +3644,7 @@ restart: if (keep) { /* set state to skip the notifier below */ state = INET6_IFADDR_STATE_DEAD; - ifa->state = 0; + ifa->state = INET6_IFADDR_STATE_PREDAD; if (!(ifa->flags & IFA_F_NODAD)) ifa->flags |= IFA_F_TENTATIVE; Patches currently in stable-queue which might be from dsahern@xxxxxxxxx are queue-4.10/ipv6-reorder-ip6_route_dev_notifier-after-ipv6_dev_notf.patch queue-4.10/net-ipv6-do-not-duplicate-dad-on-link-up.patch