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Date:	Thu, 06 Feb 2014 14:33:03 -0800
From:	Jay Vosburgh <fubar@...ibm.com>
To:	Cong Wang <cwang@...pensource.com>
cc:	Thomas Glanzmann <thomas@...nzmann.de>,
	Eric Dumazet <eric.dumazet@...il.com>,
	netdev <netdev@...r.kernel.org>,
	Veaceslav Falico <vfalico@...hat.com>, andy@...yhouse.net,
	Jiří Pírko <jiri@...nulli.us>,
	"sfeldma@...ulusnetworks.com" <sfeldma@...ulusnetworks.com>
Subject: Re: RTNL: assertion failed at net/core/dev.c (4494) and RTNL: assertion failed at net/core/rtnetlink.c (940)


Cong Wang <cwang@...pensource.com> wrote:

>On Thu, Feb 6, 2014 at 2:07 PM, Jay Vosburgh <fubar@...ibm.com> wrote:
>> Jay Vosburgh <fubar@...ibm.com> wrote:
>>
>>>Cong Wang <cwang@...pensource.com> wrote:
>>>
>>>
>>>       That would eliminate the warning, but is suboptimal.  Acquiring
>>>RTNL is not necessary on the vast majority of state machine runs
>>>(because no state changes take place, i.e., no ports are disabled or
>>>enabled).  The above change would add 10 round trips per second to RTNL,
>>>which seems excessive.
>>>
>>>       Also, we cannot unconditionally acquire RTNL in this function,
>>>as it would race with the call to cancel_delayed_work_sync from
>>>bond_close (via bond_work_cancel_all).
>
>OK.
>
>>
>>         Thought of one more problem: we can't hold a regular lock while
>> calling rtmsg_ifinfo, as it may sleep in alloc_skb.  The rtmsg_ifinfo
>> call has to be RTNL and nothing else.
>>
>
>s/GFP_KERNEL/GFP_ATOMIC/

	Yah, that would help with extra locks, but not totally solve
things.  I'm looking around, and seeing a number of other places that
will end up at one of these rtmsg_ifinfo calls with incorrect locking:

	bond_ab_arp_probe calls via bond_set_slave_active_flags and
bond_set_slave_inactive_flags without RTNL.

	bond_change_active_slave calls via bond_set_slave_inactive_flags
and bond_set_slave_active_flags with other locks held, and maybe without
RTNL; I'm not sure if bond_option_active_slave_set holds RTNL when it
calls bond_select_active_slave.

	bond_open calls via bond_set_slave_active_flags and
bond_set_slave_inactive_flags with RTNL, but also with other locks held.

	bond_loadbalance_arp_mon calls bond_set_active_slave and
bond_set_backup_slave without RTNL.

	This is in addition to the cases in the 802.3ad code from
__enable_port and __disable_port calls.

	-J

---
	-Jay Vosburgh, IBM Linux Technology Center, fubar@...ibm.com

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