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

David Miller [off-list ref] writes:

From: ebiederm@xmission.com (Eric W. Biederman)
Date: Fri, 19 Feb 2010 15:22:59 -0800

quoted

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 <redacted>

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 [off-list ref]
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 [off-list ref]
    Signed-off-by: David S. Miller [off-list ref]