netdev - Re: [patch for 2.6.24? 1/1] bonding: locking fix

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Message-ID: <Pine.LNX.4.64.0801180932440.4570@bizon.gios.gov.pl>
Date:	Fri, 18 Jan 2008 09:34:22 +0100 (CET)
From:	Krzysztof Oledzki <olel@....pl>
To:	Jay Vosburgh <fubar@...ibm.com>
cc:	Andrew Morton <akpm@...ux-foundation.org>, davem@...emloft.net,
	jeff@...zik.org, shemminger@...ux-foundation.org,
	netdev@...r.kernel.org, Andy Gospodarek <andy@...yhouse.net>
Subject: Re: [patch for 2.6.24? 1/1] bonding: locking fix 



On Thu, 17 Jan 2008, Jay Vosburgh wrote:

> Krzysztof Oledzki <olel@....pl> wrote:
>
>>> Andrew Morton <akpm@...ux-foundation.org> wrote:
>>> [...]
>>>> Can we get this bug fixed please?  Today?  It has been known about for more
>>>> than two months.
>>>
>>> 	I just reposted the complete fix; it's #1 of the series of 7.
>>
>> Bad news. :( 2.6.24-rc7 + patch #1 (bonding: fix locking in sysfs
>> primary/active selection):
> [...]
>> =========================================================
>> [ INFO: possible irq lock inversion dependency detected ]
>> 2.6.24-rc7 #1
>> ---------------------------------------------------------
>> events/0/9 just changed the state of lock:
>> (&mc->mca_lock){-+..}, at: [<c041255a>] mld_ifc_timer_expire+0x130/0x1fb
>> but this lock took another, soft-read-irq-unsafe lock in the past:
>> (&bond->lock){-.--}
>
> 	None of the seven patches I posted just a bit ago will fix this
> lockdep warning (which is a different thing that the bug Andrew inquired
> about); I'm still working on that one.
>
> 	For that one, I had posted this work in progress patch:

Yes, this one works.

> 	which makes the warning go away, but Herbert Xu pointed out that
> there is a potential problem with bond_enslave accessing the mc_lists
> without sufficient locking.  It's not the only offender, either, and the
> bond->mc_list references really need to be protected by the bond_lock,
> and the whole thing probably ought to use dev_mc_sync/unsync instead of
> what it does now.
>
> 	Since the bond_enslave, et al, business isn't a new problem, and
> I've never heard of it being hit, I'm thinking now to just leave the
> bond_enslave part for 2.6.25, and fix the lockdep warning for 2.6.24.

It is a new problem, as it never happened with <=2.6.23.

Best regards,

 				Krzysztof Olędzki