netdev - Re: [PATCH] bonding: prevent deadlock on slave store with alb mode

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Date:	Tue, 24 May 2011 22:51:26 +0200
From:	Nicolas de Pesloüan 
	<nicolas.2p.debian@...il.com>
To:	Neil Horman <nhorman@...driver.com>
CC:	Andy Gospodarek <andy@...yhouse.net>, netdev@...r.kernel.org,
	Jay Vosburgh <fubar@...ibm.com>,
	"David S. Miller" <davem@...emloft.net>
Subject: Re: [PATCH] bonding: prevent deadlock on slave store with alb mode

Le 24/05/2011 22:37, Neil Horman a écrit :

>>>> +		return -EINVAL;
>>
>> This will turn a warning into an error.
>>
> Yes, because it should have been an error all along.
>
>> This warning existed for long, but never caused the bonding setup to
>> fail. This patch cause some regression for user space. For example,
>> current ifenslave-2.6 package in Debian doesn't ensure bond is UP
>> before enslaving, because this was never required.
>>
> Thats not a regression, thats the kernel returning an error where it should have
> done so all along.  Just because a utility got away with it for awhile and it
> didn't always cause a lockup, doesn't grandfather that application in to a
> situation where the kernel has to support its broken behavior in perpituity.
>
> Besides, iirc, the ifsenslave utility still uses the ioctl path, which this
> patch doesn't touch, so ifenslave is currently unaffected (although I should
> look in the ioctl path to see if we have already added such a check, lest you be
> able to deadlock your system as previously indicated using that tool).

Unfortunately, no. Recent versions of ifenslave-2.6 on Debian don't use ioctl (ifenslave binary) 
anymore, but only sysfs.

Documentation/bonding.txt should be updated to reflect this change.
pr_warning should be changed to pr_ err.
Bonding version should be bumped.

Anyway, I will fix this package, but I suspect there exist many user scripts that don't ensure bond 
is up before enslaving.

	Nicolas.
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