Re: [PATCH net] neighbor: Reset gc_entries counter if new entry is released before insert

[Alan Maguire <alan.maguire@oracle.com>]

On Wed, 1 May 2019, David Ahern wrote:

> From: David Ahern <dsahern@gmail.com>
> 
> Ian and Alan both reported seeing overflows after upgrades to 5.x kernels:
>   neighbour: arp_cache: neighbor table overflow!
> 
> Alan's mpls script helped get to the bottom of this bug. When a new entry
> is created the gc_entries counter is bumped in neigh_alloc to check if a
> new one is allowed to be created. ___neigh_create then searches for an
> existing entry before inserting the just allocated one. If an entry
> already exists, the new one is dropped in favor of the existing one. In
> this case the cleanup path needs to drop the gc_entries counter. There
> is no memory leak, only a counter leak.
> 
> Fixes: 58956317c8d ("neighbor: Improve garbage collection")
> Reported-by: Ian Kumlien <ian.kumlien@gmail.com>
> Reported-by: Alan Maguire <alan.maguire@oracle.com>
> Signed-off-by: David Ahern <dsahern@gmail.com>
Tested-by: Alan Maguire <alan.maguire@oracle.com>
> ---
>  net/core/neighbour.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/net/core/neighbour.c b/net/core/neighbour.c
> index 30f6fd8f68e0..aff051e5521d 100644
> --- a/net/core/neighbour.c
> +++ b/net/core/neighbour.c
> @@ -663,6 +663,8 @@ static struct neighbour *___neigh_create(struct neigh_table *tbl,
>  out_tbl_unlock:
>  	write_unlock_bh(&tbl->lock);
>  out_neigh_release:
> +	if (!exempt_from_gc)
> +		atomic_dec(&tbl->gc_entries);
>  	neigh_release(n);
>  	goto out;
>  }
> -- 
> 2.11.0
> 
>