netdev - Re: [PATCH 1/2] net: Fix sysctl restarts...

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Date:	Fri, 19 Feb 2010 15:35:27 -0800
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	David Miller <davem@...emloft.net>
Cc:	netdev@...r.kernel.org
Subject: Re: [PATCH 1/2] net: Fix sysctl restarts...

David Miller <davem@...emloft.net> writes:

> From: ebiederm@...ssion.com (Eric W. Biederman)
> Date: Fri, 19 Feb 2010 15:22:59 -0800
>
>> 
>> Yuck.  It turns out that when we restart sysctls we were restarting
>> with the values already changed.  Which unfortunately meant that
>> the second time through we thought there was no change and skipped
>> all kinds of work, despite the fact that there was indeed a change.
>> 
>> I have fixed this the simplest way possible by restoring the changed
>> values when we restart the sysctl write.
>> 
>> One of my coworkers spotted this bug when after disabling forwarding
>> on an interface pings were still forwarded.
>> 
>> Signed-off-by: Eric W. Biederman <ebiederm@...ssion.com>
>
> What commit added this bug?

When we I fixed the deadlock that can happen if you write to forwarding
while removing the device.  The deadlock was fixed, the restart worked
but I somehow missed the fact that proc_dointvec modifies state and so
defeated the change detection.  *embarrassing*

commit 9b8adb5ea005fe73acd5dd58f9bd47eafa74c9d1
Author: Eric W. Biederman <ebiederm@...ssion.com>
Date:   Wed May 13 16:59:21 2009 +0000

    net: Fix devinet_sysctl_forward
    
    sysctls are unregistered with the rntl_lock held making
    it unsafe to unconditionally grab the the rtnl_lock.  Instead
    we need to call rtnl_trylock and restart the system call
    if we can not grab it.  Otherwise we could deadlock at unregistration
    time.
    
    Signed-off-by: Eric W. Biederman <ebiederm@...stanetworks.com>
    Signed-off-by: David S. Miller <davem@...emloft.net>




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