From mboxrd@z Thu Jan 1 00:00:00 1970 From: Eric Dumazet Subject: Re: [PATCH net] ipv6: rate-limit probes for neighbourless routes Date: Fri, 12 Oct 2018 08:17:28 -0700 Message-ID: References: Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Cc: Stefano Brivio To: Sabrina Dubroca , netdev@vger.kernel.org Return-path: Received: from mail-pl1-f195.google.com ([209.85.214.195]:44097 "EHLO mail-pl1-f195.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728182AbeJLWu1 (ORCPT ); Fri, 12 Oct 2018 18:50:27 -0400 Received: by mail-pl1-f195.google.com with SMTP id p25-v6so6075015pli.11 for ; Fri, 12 Oct 2018 08:17:31 -0700 (PDT) In-Reply-To: Content-Language: en-US Sender: netdev-owner@vger.kernel.org List-ID: On 10/12/2018 07:22 AM, Sabrina Dubroca wrote: > When commit 270972554c91 ("[IPV6]: ROUTE: Add Router Reachability > Probing (RFC4191).") introduced router probing, the rt6_probe() function > required that a neighbour entry existed. This neighbour entry is used to > record the timestamp of the last probe via the ->updated field. > > Later, commit 2152caea7196 ("ipv6: Do not depend on rt->n in rt6_probe().") > removed the requirement for a neighbour entry. Neighbourless routes skip > the interval check and are not rate-limited. > Interesting. Can you describe a little more what happens here ? Could this explain gazillions of syzbot/syzkaller reports that have all in common : rcu: INFO: rcu_preempt detected stalls on CPUs/tasks: Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 Call Trace: rcu: (detected by 0, t=10712 jiffies, g=90369, q=135) __dump_stack lib/dump_stack.c:77 [inline] dump_stack+0x1c4/0x2b4 lib/dump_stack.c:113 rcu: All QSes seen, last rcu_preempt kthread activity 10548 (4295003843-4294993295), jiffies_till_next_fqs=1, root ->qsmask 0x0 syz-executor0 R running task warn_alloc.cold.119+0xb7/0x1bd mm/page_alloc.c:3426 22896 7592 5826 0x8010000c Call Trace: sched_show_task.cold.83+0x2b6/0x30a kernel/sched/core.c:5296 __alloc_pages_slowpath+0x2667/0x2d80 mm/page_alloc.c:4297 print_other_cpu_stall.cold.79+0xa83/0xba5 kernel/rcu/tree.c:1430 check_cpu_stall kernel/rcu/tree.c:1557 [inline] __rcu_pending kernel/rcu/tree.c:3276 [inline] rcu_pending kernel/rcu/tree.c:3319 [inline] rcu_check_callbacks+0xafc/0x1990 kernel/rcu/tree.c:2665 __alloc_pages_nodemask+0xa80/0xde0 mm/page_alloc.c:4390 __alloc_pages include/linux/gfp.h:473 [inline] __alloc_pages_node include/linux/gfp.h:486 [inline] kmem_getpages mm/slab.c:1409 [inline] cache_grow_begin+0x91/0x8c0 mm/slab.c:2677 fallback_alloc+0x203/0x2e0 mm/slab.c:3219 ____cache_alloc_node+0x1c7/0x1e0 mm/slab.c:3287 slab_alloc_node mm/slab.c:3327 [inline] kmem_cache_alloc_node+0xe3/0x730 mm/slab.c:3642 __alloc_skb+0x119/0x770 net/core/skbuff.c:193 alloc_skb include/linux/skbuff.h:997 [inline] ndisc_alloc_skb+0x144/0x340 net/ipv6/ndisc.c:403 ndisc_send_rs+0x331/0x6e0 net/ipv6/ndisc.c:669 update_process_times+0x2d/0x70 kernel/time/timer.c:1636 addrconf_rs_timer+0x314/0x690 net/ipv6/addrconf.c:3836 tick_sched_handle+0x9f/0x180 kernel/time/tick-sched.c:164 tick_sched_timer+0x45/0x130 kernel/time/tick-sched.c:1274 __run_hrtimer kernel/time/hrtimer.c:1398 [inline] __hrtimer_run_queues+0x41c/0x10d0 kernel/time/hrtimer.c:1460 call_timer_fn+0x272/0x920 kernel/time/timer.c:1326 hrtimer_interrupt+0x313/0x780 kernel/time/hrtimer.c:1518