Subject: Re: [PATCH 2/3] netlink: Mark dumps as inconsistent which have been interrupted by a resize

From: Ying Xue <[email-masked]>
Date: Wed, 21 Jan 2015 16:13:56 +0800

On 01/20/2015 09:20 PM, Thomas Graf wrote:
> A deferred resize of nl_table causes the offsets that Netlink diag keeps
> to become inaccurate. Mark the dump as inconsistent and have user space
> request a new dump.
> 
> Signed-off-by: Thomas Graf <[email-masked]>
> ---
>  net/netlink/af_netlink.c | 10 ++++++++++
>  net/netlink/af_netlink.h |  1 +
>  net/netlink/diag.c       |  1 +
>  3 files changed, 12 insertions(+)
> 
> diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c
> index 7a94185..e214557 100644
> --- a/net/netlink/af_netlink.c
> +++ b/net/netlink/af_netlink.c
> @@ -91,6 +91,9 @@ static inline int netlink_is_kernel(struct sock *sk)
>  struct netlink_table *nl_table;
>  EXPORT_SYMBOL_GPL(nl_table);
>  
> +atomic_t nl_table_seq;

It sounds like the atomic variable is not initialized.

Regards,
Ying

> +EXPORT_SYMBOL_GPL(nl_table_seq);
> +
>  static DECLARE_WAIT_QUEUE_HEAD(nl_table_wait);
>  
>  static int netlink_dump(struct sock *sk);
> @@ -3071,6 +3074,12 @@ static const struct net_proto_family netlink_family_ops = {
>  	.owner	= THIS_MODULE,	/* for consistency 8) */
>  };
>  
> +static void nl_table_resize_notify(const struct rhashtable *ht,
> +				   enum rht_resize_op op)
> +{
> +	atomic_inc(&nl_table_seq);
> +}
> +
>  static int __net_init netlink_net_init(struct net *net)
>  {
>  #ifdef CONFIG_PROC_FS
> @@ -3124,6 +3133,7 @@ static int __init netlink_proto_init(void)
>  		.max_shift = 16, /* 64K */
>  		.grow_decision = rht_grow_above_75,
>  		.shrink_decision = rht_shrink_below_30,
> +		.resize_notify = nl_table_resize_notify,
>  	};
>  
>  	if (err != 0)
> diff --git a/net/netlink/af_netlink.h b/net/netlink/af_netlink.h
> index 7518375..51c23c0 100644
> --- a/net/netlink/af_netlink.h
> +++ b/net/netlink/af_netlink.h
> @@ -74,5 +74,6 @@ struct netlink_table {
>  
>  extern struct netlink_table *nl_table;
>  extern rwlock_t nl_table_lock;
> +extern atomic_t nl_table_seq;
>  
>  #endif
> diff --git a/net/netlink/diag.c b/net/netlink/diag.c
> index 3ee63a3..50aa385 100644
> --- a/net/netlink/diag.c
> +++ b/net/netlink/diag.c
> @@ -112,6 +112,7 @@ static int __netlink_diag_dump(struct sk_buff *skb, struct netlink_callback *cb,
>  	int ret = 0, num = 0, i;
>  
>  	req = nlmsg_data(cb->nlh);
> +	cb->seq = atomic_read(&nl_table_seq);
>  
>  	for (i = 0; i < htbl->size; i++) {
>  		struct rhash_head *pos;
>