Re: [PATCH net-next v3 7/7] mld: add mc_lock for protecting per-interface mld data

Taehee Yoo
2021-03-30T15:02:10Z

On 3/30/21 9:24 PM, Eric Dumazet wrote:
>
>
> On 3/30/21 1:59 PM, Eric Dumazet wrote:
>>
>>
>> On 3/25/21 5:16 PM, Taehee Yoo wrote:
>>> The purpose of this lock is to avoid a bottleneck in the query/report
>>> event handler logic.
>>>
>>> By previous patches, almost all mld data is protected by RTNL.
>>> So, the query and report event handler, which is data path logic
>>> acquires RTNL too. Therefore if a lot of query and report events
>>> are received, it uses RTNL for a long time.
>>> So it makes the control-plane bottleneck because of using RTNL.
>>> In order to avoid this bottleneck, mc_lock is added.
>>>
>>> mc_lock protect only per-interface mld data and per-interface mld
>>> data is used in the query/report event handler logic.
>>> So, no longer rtnl_lock is needed in the query/report event handler
logic.
>>> Therefore bottleneck will be disappeared by mc_lock.
>>>
>>
>> What testsuite have you run exactly to validate this monster patch ?
>>

I've been using an application, which calls setsockopt() with the below
options.
IPV6_ADD_MEMBERSHIP
IPV6_DROP_MEMBERSHIP
MCAST_JOIN_SOURCE_GROUP
MCAST_LEAVE_SOURCE_GROUP
MCAST_BLOCK_SOURCE
MCAST_UNBLOCK_SOURCE
MCAST_MSFILTER
And checks out /proc/net/mcfilter6 and /proc/net/igmp6.

>> Have you used CONFIG_LOCKDEP=y / CONFIG_DEBUG_ATOMIC_SLEEP=y ?
>>

Yes, I'm using both configs.

>>> Suggested-by: Cong Wang <xiyou.wangcong@gmail.com>
>>> Signed-off-by: Taehee Yoo <ap420073@gmail.com>
>>
>> [...]
>>
>>> /*
>>> - * device multicast group del
>>> + * device multicast group del
>>> */
>>> int __ipv6_dev_mc_dec(struct inet6_dev *idev, const struct
in6_addr *addr)
>>> {
>>> @@ -943,8 +967,9 @@ int __ipv6_dev_mc_dec(struct inet6_dev *idev,
const struct in6_addr *addr)
>>>
>>> ASSERT_RTNL();
>>>
>>> + mutex_lock(&idev->mc_lock);
>>> for (map = &idev->mc_list;
>>> - (ma = rtnl_dereference(*map));
>>> + (ma = mc_dereference(*map, idev));
>>> map = &ma->next) {
>>> if (ipv6_addr_equal(&ma->mca_addr, addr)) {
>>> if (--ma->mca_users == 0) {
>>
>> This can be called with rcu_bh held, thus :
>>
>> BUG: sleeping function called from invalid context at
kernel/locking/mutex.c:928
>> in_atomic(): 1, irqs_disabled(): 0, non_block: 0, pid: 4624, name:
kworker/1:2
>> 4 locks held by kworker/1:2/4624:
>> #0: ffff88802135d138 ((wq_completion)ipv6_addrconf){+.+.}-{0:0},
at: arch_atomic64_set arch/x86/include/asm/atomic64_64.h:34 [inline]
>> #0: ffff88802135d138 ((wq_completion)ipv6_addrconf){+.+.}-{0:0},
at: atomic64_set include/asm-generic/atomic-instrumented.h:856 [inline]
>> #0: ffff88802135d138 ((wq_completion)ipv6_addrconf){+.+.}-{0:0},
at: atomic_long_set include/asm-generic/atomic-long.h:41 [inline]
>> #0: ffff88802135d138 ((wq_completion)ipv6_addrconf){+.+.}-{0:0},
at: set_work_data kernel/workqueue.c:616 [inline]
>> #0: ffff88802135d138 ((wq_completion)ipv6_addrconf){+.+.}-{0:0},
at: set_work_pool_and_clear_pending kernel/workqueue.c:643 [inline]
>> #0: ffff88802135d138 ((wq_completion)ipv6_addrconf){+.+.}-{0:0},
at: process_one_work+0x871/0x1600 kernel/workqueue.c:2246
>> #1: ffffc90009adfda8 ((addr_chk_work).work){+.+.}-{0:0}, at:
process_one_work+0x8a5/0x1600 kernel/workqueue.c:2250
>> #2: ffffffff8d66d328 (rtnl_mutex){+.+.}-{3:3}, at:
addrconf_verify_work+0xa/0x20 net/ipv6/addrconf.c:4572
>> #3: ffffffff8bf74300 (rcu_read_lock_bh){....}-{1:2}, at:
addrconf_verify_rtnl+0x2b/0x1150 net/ipv6/addrconf.c:4459
>> Preemption disabled at:
>> [<ffffffff87b39f41>] local_bh_disable include/linux/bottom_half.h:19
[inline]
>> [<ffffffff87b39f41>] rcu_read_lock_bh include/linux/rcupdate.h:727
[inline]
>> [<ffffffff87b39f41>] addrconf_verify_rtnl+0x41/0x1150
net/ipv6/addrconf.c:4461
>> CPU: 1 PID: 4624 Comm: kworker/1:2 Not tainted 5.12.0-rc4-syzkaller #0
>> Hardware name: Google Google Compute Engine/Google Compute Engine,
BIOS Google 01/01/2011
>> Workqueue: ipv6_addrconf addrconf_verify_work
>> Call Trace:
>> __dump_stack lib/dump_stack.c:79 [inline]
>> dump_stack+0x141/0x1d7 lib/dump_stack.c:120
>> ___might_sleep.cold+0x1f1/0x237 kernel/sched/core.c:8328
>> __mutex_lock_common kernel/locking/mutex.c:928 [inline]
>> __mutex_lock+0xa9/0x1120 kernel/locking/mutex.c:1096
>> __ipv6_dev_mc_dec+0x5f/0x340 net/ipv6/mcast.c:970
>> addrconf_leave_solict net/ipv6/addrconf.c:2182 [inline]
>> addrconf_leave_solict net/ipv6/addrconf.c:2174 [inline]
>> __ipv6_ifa_notify+0x5b6/0xa90 net/ipv6/addrconf.c:6077
>> ipv6_ifa_notify net/ipv6/addrconf.c:6100 [inline]
>> ipv6_del_addr+0x463/0xae0 net/ipv6/addrconf.c:1294
>> addrconf_verify_rtnl+0xd59/0x1150 net/ipv6/addrconf.c:4488
>> addrconf_verify_work+0xf/0x20 net/ipv6/addrconf.c:4573
>> process_one_work+0x98d/0x1600 kernel/workqueue.c:2275
>> worker_thread+0x64c/0x1120 kernel/workqueue.c:2421
>> kthread+0x3b1/0x4a0 kernel/kthread.c:292
>> ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:294
>>
>
> I will test this fix:

Thanks a lot!

>
> diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
> index
120073ffb666b18678e3145d91dac59fa865a592..8f3883f4cb4a15a0749b8f0fe00061e483ea26ca
100644
> --- a/net/ipv6/addrconf.c
> +++ b/net/ipv6/addrconf.c
> @@ -4485,7 +4485,9 @@ static void addrconf_verify_rtnl(void)
> age >= ifp->valid_lft) {
> spin_unlock(&ifp->lock);
> in6_ifa_hold(ifp);
> + rcu_read_unlock_bh();
> ipv6_del_addr(ifp);
> + rcu_read_lock_bh();
> goto restart;
> } else if (ifp->prefered_lft ==
INFINITY_LIFE_TIME) {
> spin_unlock(&ifp->lock);
>