netdev - Re: RTNL: assertion failed at net/core/dev.c (4494) and RTNL: assertion failed at net/core/rtnetlink.c (940)

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Date:	Thu, 06 Feb 2014 14:07:42 -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>
Subject: Re: RTNL: assertion failed at net/core/dev.c (4494) and RTNL: assertion failed at net/core/rtnetlink.c (940)

Jay Vosburgh <fubar@...ibm.com> wrote:

>Cong Wang <cwang@...pensource.com> wrote:
>
>>On Thu, Feb 6, 2014 at 12:51 PM, Thomas Glanzmann <thomas@...nzmann.de> wrote:
>>> Hello,
>>> this morning I checked out Linus tip and compiled it after booting my
>>> dmesg is full of:
>>>
>>> [    8.944991] RTNL: assertion failed at net/core/dev.c (4494)
>>> [    8.950640] CPU: 3 PID: 388 Comm: kworker/u24:4 Not tainted 3.14.0-rc1+ #3
>>> [    8.950642] Hardware name: Supermicro X9SRD-F/X9SRD-F, BIOS 1.0a 10/15/2012
>>> [    8.950654] Workqueue: bond0 bond_3ad_state_machine_handler [bonding]
>>> [    8.950658]  0000000000000000 ffff881020c88000 ffffffff8138e219 ffff881020c88000
>>> [    8.950664]  ffffffff812d3091 ffff881023961040 ffffffff812e3132 0000000000000246
>>> [    8.950670]  0000000000000020 ffff881020ab1be8 0000000020ab1ba8 0000000000000000
>>> [    8.950675] Call Trace:
>>> [    8.950686]  [<ffffffff8138e219>] ? dump_stack+0x41/0x51
>>> [    8.950694]  [<ffffffff812d3091>] ? netdev_master_upper_dev_get+0x2a/0x4d
>>> [    8.950699]  [<ffffffff812e3132>] ? rtnl_fill_ifinfo+0x2c/0xac4
>>> [    8.950707]  [<ffffffff81072211>] ? print_time.part.5+0x50/0x54
>>> [    8.950715]  [<ffffffff812caf94>] ? __kmalloc_reserve.isra.42+0x2a/0x6d
>>> [    8.950721]  [<ffffffff81102040>] ? ksize+0x12/0x1e
>>> [    8.950726]  [<ffffffff812cb2b7>] ? __alloc_skb+0xb5/0x1a9
>>> [    8.950731]  [<ffffffff812e4626>] ? rtmsg_ifinfo+0x6c/0xd6
>>> [    8.950739]  [<ffffffffa035f4f9>] ? __enable_port.isra.17+0x51/0x5a [bonding]
>>> [    8.950747]  [<ffffffffa0360463>] ? ad_agg_selection_logic+0x3d3/0x3ed [bonding]
>>> [    8.950754]  [<ffffffffa0360d40>] ? bond_3ad_state_machine_handler+0x555/0x918 [bonding]
>>> [    8.950761]  [<ffffffff8104db2d>] ? process_one_work+0x191/0x293
>>> [    8.950766]  [<ffffffff8104dfde>] ? worker_thread+0x121/0x1e7
>>> [    8.950770]  [<ffffffff8104debd>] ? rescuer_thread+0x269/0x269
>>> [    8.950777]  [<ffffffff810527b6>] ? kthread+0x99/0xa1
>>> [    8.950782]  [<ffffffff8105271d>] ? __kthread_parkme+0x59/0x59
>>> [    8.950789]  [<ffffffff8139733c>] ? ret_from_fork+0x7c/0xb0
>>> [    8.950794]  [<ffffffff8105271d>] ? __kthread_parkme+0x59/0x59
>>
>>
>>Hmm, rtmsg_ifinfo() should be called with rtnl lock, but
>>__enable_port() is called
>>with rcu_read_lock() which means we can't block inside it, therefore we probably
>>should take rtnl lock outside:
>>
>>diff --git a/drivers/net/bonding/bond_3ad.c b/drivers/net/bonding/bond_3ad.c
>>index cce1f1b..3c09ffa 100644
>>--- a/drivers/net/bonding/bond_3ad.c
>>+++ b/drivers/net/bonding/bond_3ad.c
>>@@ -2065,6 +2065,7 @@ void bond_3ad_state_machine_handler(struct
>>work_struct *work)
>>        struct slave *slave;
>>        struct port *port;
>>
>>+       rtnl_lock();
>>        read_lock(&bond->lock);
>>        rcu_read_lock();
>>
>>@@ -2123,6 +2124,7 @@ void bond_3ad_state_machine_handler(struct
>>work_struct *work)
>> re_arm:
>>        rcu_read_unlock();
>>        read_unlock(&bond->lock);
>>+       rtnl_unlock();
>>        queue_delayed_work(bond->wq, &bond->ad_work, ad_delta_in_ticks);
>> }
>
>	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).

	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.

	-J

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

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