Subject: Re: [PATCH v2] notifier: Fix soft lockup for notifier_call_chain().

From: Ding Tianhong <[email-masked]>
Date: Tue, 28 Jun 2016 14:09:33 +0800

On 2016/6/28 13:13, Eric Dumazet wrote:
> On Tue, 2016-06-28 at 12:56 +0800, Ding Tianhong wrote:
>> The problem was occurs in my system that a lot of drviers register
>> its own handler to the notifiler call chain for netdev_chain, and
>> then create 4095 vlan dev for one nic, and add several ipv6 address
>> on each one of them, just like this:
>>
>> for i in `seq 1 4095`; do ip link add link eth0 name eth0.$i type vlan id $i; done
>> for i in `seq 1 4095`; do ip -6 addr add 2001::$i dev eth0.$i; done
>> for i in `seq 1 4095`; do ip -6 addr add 2002::$i dev eth0.$i; done
>> for i in `seq 1 4095`; do ip -6 addr add 2003::$i dev eth0.$i; done
>>
>> ifconfig eth0 up
>> ifconfig eth0 down
> 
> I would very much prefer cond_resched() at a more appropriate place.
> 
> touch_nmi_watchdog() does not fundamentally solve the issue, as some
> process is holding one cpu for a very long time.
> 
> Probably in addrconf_ifdown(), as if you have 100,000 IPv6 addresses on
> a single netdev, this function might also trigger a soft lockup, without
> playing with 4096 vlans...
> 
> diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
> index a1f6b7b315317f811cafbf386cf21dfc510c2010..13b675f79a751db45af28fc0474ddb17d9b69b06 100644
> --- a/net/ipv6/addrconf.c
> +++ b/net/ipv6/addrconf.c
> @@ -3566,6 +3566,7 @@ restart:
>  			}
>  		}
>  		spin_unlock_bh(&addrconf_hash_lock);
> +		cond_resched();
>  	}
>  
>  	write_lock_bh(&idev->lock);
> 
> 
it looks like not enough, I still got this calltrace,

<4>[ 7618.596184]3840: ffffffbfa101a0a0 00000000000007f0
<4>[ 7618.596187][<ffffffc000203780>] el1_irq+0x80/0x100
<4>[ 7618.596255][<ffffffbfa1019d74>] fib6_walk_continue+0x1d4/0x200 [ipv6]
<4>[ 7618.596275][<ffffffbfa1019ed4>] fib6_walk+0x3c/0x70 [ipv6]
<4>[ 7618.596295][<ffffffbfa1019f70>] fib6_clean_tree+0x68/0x90 [ipv6]
<4>[ 7618.596314][<ffffffbfa101a020>] __fib6_clean_all+0x88/0xc0 [ipv6]
<4>[ 7618.596334][<ffffffbfa101c7f0>] fib6_run_gc+0x88/0x148 [ipv6]
<4>[ 7618.596354][<ffffffbfa1021678>] ndisc_netdev_event+0x80/0x140 [ipv6]
<4>[ 7618.596358][<ffffffc00023f83c>] notifier_call_chain+0x5c/0xa0
<4>[ 7618.596361][<ffffffc00023f9e0>] raw_notifier_call_chain+0x20/0x28
<4>[ 7618.596366][<ffffffc0005cbab4>] call_netdevice_notifiers_info+0x4c/0x80
<4>[ 7618.596369][<ffffffc0005cbfc8>] dev_close_many+0xd0/0x138
<4>[ 7618.596378][<ffffffbfa33be6e8>] vlan_device_event+0x4a8/0x6a0 [8021q]
<4>[ 7618.596381][<ffffffc00023f83c>] notifier_call_chain+0x5c/0xa0
<4>[ 7618.596384][<ffffffc00023f9e0>] raw_notifier_call_chain+0x20/0x28
<4>[ 7618.596387][<ffffffc0005cbab4>] call_netdevice_notifiers_info+0x4c/0x80
<4>[ 7618.596390][<ffffffc0005d5148>] __dev_notify_flags+0xb8/0xe0
<4>[ 7618.596393][<ffffffc0005d5994>] dev_change_flags+0x54/0x68
<4>[ 7618.596397][<ffffffc00064a620>] devinet_ioctl+0x650/0x700
<4>[ 7618.596400][<ffffffc00064bea4>] inet_ioctl+0xa4/0xc8
<4>[ 7618.596405][<ffffffc0005b1094>] sock_do_ioctl+0x44/0x88
<4>[ 7618.596408][<ffffffc0005b1a3c>] sock_ioctl+0x23c/0x308
<4>[ 7618.596413][<ffffffc000393bc4>] do_vfs_ioctl+0x48c/0x620

> .