# Re: \[net PATCH v3 3/3\] net: netprio: fix cgrp create and write priomap race

- From: Neil Horman \<nhorman@tuxdriver.com\>
- Date: 2012-08-15 10:56:25 
- List: netdev
- Page: https://ratatoskr.run/netdev/2012/08/3908581
- Thread: https://ratatoskr.run/netdev/2012/08/3908401/t.md

```text
On Tue, Aug 14, 2012 at 03:34:35PM -0700, John Fastabend wrote:
> A race exists where creating cgroups and also updating the priomap
> may result in losing a priomap update. This is because priomap
> writers are not protected by rtnl_lock.
> 
> Move priority writer into rtnl_lock()/rtnl_unlock().
> 
> CC: Neil Horman <nhorman@tuxdriver.com>
> Reported-by: Al Viro <viro@ZenIV.linux.org.uk>
> Signed-off-by: John Fastabend <redacted>
> ---
> 
>  net/core/netprio_cgroup.c |    8 +++-----
>  1 files changed, 3 insertions(+), 5 deletions(-)
> 
> diff --git a/net/core/netprio_cgroup.c b/net/core/netprio_cgroup.c
> index f65dba3..c75e3f9 100644
> --- a/net/core/netprio_cgroup.c
> +++ b/net/core/netprio_cgroup.c
> @@ -101,12 +101,10 @@ static int write_update_netdev_table(struct net_device *dev)
>  	u32 max_len;
>  	struct netprio_map *map;
>  
> -	rtnl_lock();
>  	max_len = atomic_read(&max_prioidx) + 1;
>  	map = rtnl_dereference(dev->priomap);
>  	if (!map || map->priomap_len < max_len)
>  		ret = extend_netdev_table(dev, max_len);
> -	rtnl_unlock();
>  
>  	return ret;
>  }
> @@ -256,17 +254,17 @@ static int write_priomap(struct cgroup *cgrp, struct cftype *cft,
>  	if (!dev)
>  		goto out_free_devname;
>  
> +	rtnl_lock();
>  	ret = write_update_netdev_table(dev);
>  	if (ret < 0)
>  		goto out_put_dev;
>  
> -	rcu_read_lock();
> -	map = rcu_dereference(dev->priomap);
> +	map = rtnl_dereference(dev->priomap);
>  	if (map)
>  		map->priomap[prioidx] = priority;
> -	rcu_read_unlock();
>  
>  out_put_dev:
> +	rtnl_unlock();
>  	dev_put(dev);
>  
>  out_free_devname:
> 
> 

Acked-by: Neil Horman <nhorman@tuxdriver.com>
```