netdev - Re: [PATCH 1/1] bonding: eliminate RTNL assertion spew

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Date:	Tue, 9 Jan 2007 15:09:35 -0800
From:	Stephen Hemminger <shemminger@...l.org>
To:	Andy Gospodarek <andy@...yhouse.net>
Cc:	fubar@...ibm.com, netdev@...r.kernel.org
Subject: Re: [PATCH 1/1] bonding: eliminate RTNL assertion spew

On Tue, 9 Jan 2007 17:59:01 -0500
Andy Gospodarek <andy@...yhouse.net> wrote:

> 
> These changes eliminate the messages indicating that the rtnetlink lock
> isn't held when bonding tries to change the MAC address of an interface.
> These calls generally come from timer-pops, but also from sysfs events
> since neither hold the rtnl lock.  
> 
> The spew generally looks something like this:
> 
> RTNL: assertion failed at net/core/fib_rules.c (391)
>  [<c028d12e>] fib_rules_event+0x3a/0xeb
>  [<c02da576>] notifier_call_chain+0x19/0x29
>  [<c0280ce6>] dev_set_mac_address+0x46/0x4b
>  [<f8a2a686>] alb_set_slave_mac_addr+0x5d/0x88 [bonding]
>  [<f8a2aa7e>] alb_swap_mac_addr+0x88/0x134 [bonding]
>  [<f8a25ed9>] bond_change_active_slave+0x1a1/0x2c5 [bonding]
>  [<f8a262e8>] bond_select_active_slave+0xa8/0xe1 [bonding]
>  [<f8a27ecb>] bond_mii_monitor+0x3af/0x3fd [bonding]
>  [<c0121896>] run_workqueue+0x85/0xc5
>  [<f8a27b1c>] bond_mii_monitor+0x0/0x3fd [bonding]
>  [<c0121d83>] worker_thread+0xe8/0x119
>  [<c0111179>] default_wake_function+0x0/0xc
>  [<c0121c9b>] worker_thread+0x0/0x119
>  [<c0124099>] kthread+0xad/0xd8
>  [<c0123fec>] kthread+0x0/0xd8
>  .....
> 
> This patch was mostly inspired from parts of some potential bonding
> updates Jay Vosburgh <fubar@...ibm.com> and I discussed in December, so
> he deserves most of the credit for the idea.
> 
> I've tested it on several systems and it works as I expect.  Deadlocks
> between the rtnl and global bond lock are avoided since we drop the
> global bond lock before taking the rtnl lock.
> 


This seems like the ugly way to do it. Couldn't you just change figure out
how to acquire RTNL first. It wouldn't hurt to acquire it in the monitor
routine even if you don't need it.

Conditional locking is a bad road to start down.
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