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: f1705ec197 ("net: ipv6: Make address flushing on ifdown optional")
Reported-by: Andrey Konovalov <andreyknvl@google.com>
Signed-off-by: David Ahern <dsahern@gmail.com>
Tested-by: Andrey Konovalov <andreyknvl@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
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