[libvirt] [PATCH] nwfilter: serialize execution of scripts with ebtables cmds

[Stefan Berger]

libvir-list-bounces at redhat.com wrote on 08/13/2010 03:08:11 PM:

> [image removed] 
> 
> Re: [libvirt] [PATCH] nwfilter: serialize execution of scripts with 
> ebtables cmds
> 
> Eric Blake 
> 
> to:
> 
> Stefan Berger
> 
> 08/13/2010 03:17 PM
> 
> Sent by:
> 
> libvir-list-bounces at redhat.com
> 
> Cc:
> 
> libvir-list
> 
> On 08/13/2010 12:35 PM, Stefan Berger wrote:
> >  While testing the SIGHUP handling and reloading of the nwfilter 
driver,
> > I found that when the filters are rebuilt and mutlipe threads handled
> > the individual interfaces, concurrently running multiple external bash
> > scripts causes strange failures even though the executed ebtables
> > commands are working on different tables for different interfaces. I
> > cannot say for sure where the concurrency problems are caused, but
> > introducing this lock definitely helps.
> > 
> > Signed-off-by: Stefan Berger <stefanb at us.ibm.com>
> 
> ACK.

I'll push this shortly. For the record, here two scripts, that each 
execute fine but once run concurrently cause a race.

script 1:

#!/bin/bash
dev=xyzdev
while test 1; do
   ebtables -t nat -A PREROUTING -i ${dev} -j ACCEPT
   if [ $? -ne 0 ]; then
       echo "odd!"
   fi
   ebtables -t nat -D PREROUTING -i ${dev} -j ACCEPT
   if [ $? -ne 0 ]; then
       echo "odd!"
   fi

script 2:

#!/bin/bash
dev=xyzdev2
while test 1; do
   ebtables -t nat -A PREROUTING -i ${dev} -j ACCEPT
   if [ $? -ne 0 ]; then
       echo "odd!"
   fi
   ebtables -t nat -D PREROUTING -i ${dev} -j ACCEPT
   if [ $? -ne 0 ]; then
       echo "odd!"
   fi


Output when run concurrently:

The kernel doesn't support a certain ebtables extension, consider 
recompiling your kernel or insmod the extension.
odd!
The kernel doesn't support a certain ebtables extension, consider 
recompiling your kernel or insmod the extension.
odd!


   Stefan
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