Re: [PATCH 1/7] netfilter: use a linked list of loggers.

[Patrick McHardy <kaber@trash.net>]

Eric Leblond wrote:
> This patch modifies nf_log to use a linked list of loggers for each
> protocol. It also separate registration and binding. To be used as
> logging module, a module has to register calling nf_log_register()
> and to bind to a protocol it has to call nf_log_bind_pf().
> 
> Signed-off-by: Eric Leblond <eric@inl.fr>
> ---
>  include/net/netfilter/nf_log.h |   10 +++-
>  net/netfilter/nf_log.c         |  107 +++++++++++++++++++++++++++++++---------
>  2 files changed, 91 insertions(+), 26 deletions(-)
> 
> diff --git a/net/netfilter/nf_log.c b/net/netfilter/nf_log.c
> index fa8ae5d..8a5e4aa 100644
> --- a/net/netfilter/nf_log.c
> +++ b/net/netfilter/nf_log.c
> @@ -14,13 +14,25 @@
>     LOG target modules */
>  
>  #define NF_LOG_PREFIXLEN		128
> +#define NFLOGGER_NAME_LEN		12

Just wondering what this limit is based on, I can't seem to
fine anything requiring a limit at all since the names are
const char *.

>  static const struct nf_logger *nf_loggers[NFPROTO_NUMPROTO] __read_mostly;
> -static DEFINE_MUTEX(nf_log_mutex);
> +static struct list_head nf_loggers_l[NFPROTO_NUMPROTO] __read_mostly;
> +static DEFINE_SPINLOCK(nf_log_lock);

I don't understand how locking is supposed to work now. You change
the mutex to a spinlock and use it with _bh everywhere, yet I don't
see a single spot thats called outside of process context and the
RCU assignments are still present.

The users of nf_log_register are also not converted simultaneously,
so this patch breaks bisection.

> @@ -29,50 +41,91 @@ int nf_log_register(u_int8_t pf, const struct nf_logger *logger)
>  
>  	/* Any setup of logging members must be done before
>  	 * substituting pointer. */
> -	ret = mutex_lock_interruptible(&nf_log_mutex);
> -	if (ret < 0)
> -		return ret;
> -
> -	if (!nf_loggers[pf])
> -		rcu_assign_pointer(nf_loggers[pf], logger);
> -	else if (nf_loggers[pf] == logger)
> -		ret = -EEXIST;
> -	else
> -		ret = -EBUSY;
> -
> -	mutex_unlock(&nf_log_mutex);
> +	spin_lock_bh(&nf_log_lock);
> +
> +	ret = -EEXIST;
> +	if (pf == NFPROTO_UNSPEC) {
> +		int i;
> +		for (i = NFPROTO_UNSPEC; i < NFPROTO_NUMPROTO; i++) {
> +			if (__find_logger(i, logger->name) == NULL) {
> +				ret = 0;
> +				INIT_LIST_HEAD(&(logger->list[i]));

This is not necessary, list_add_* doesn't require the new element
to be initialized. Also please remove the unneeded parens (same
remarks for below).

> +				list_add_tail(&(logger->list[i]),
> +						  &(nf_loggers_l[i]));
> +			}
> +		}
> +	} else {
> +		if (__find_logger(pf, logger->name) == NULL) {
> +			ret = 0;
> +			INIT_LIST_HEAD(&(logger->list[pf]));
> +			/* register at end of list to honor first register win */
> +			list_add_tail(&(logger->list[pf]),
> +					  &nf_loggers_l[pf]);
> +		}
> +	}
> +
> +	spin_unlock_bh(&nf_log_lock);
>  	return ret;
>  }
>  EXPORT_SYMBOL(nf_log_register);
>  
>  void nf_log_unregister_pf(u_int8_t pf)
>  {
> +	struct nf_logger *e;
>  	if (pf >= ARRAY_SIZE(nf_loggers))
>  		return;
> -	mutex_lock(&nf_log_mutex);
> -	rcu_assign_pointer(nf_loggers[pf], NULL);
> -	mutex_unlock(&nf_log_mutex);
> +	spin_lock_bh(&nf_log_lock);
> +	list_for_each_entry(e, &(nf_loggers_l[pf]), list[pf])
> +		list_del(&(e->list[pf]));
> +	spin_unlock_bh(&nf_log_lock);
>  
>  	/* Give time to concurrent readers. */
>  	synchronize_rcu();
>  }
>  EXPORT_SYMBOL(nf_log_unregister_pf);
>  
> -void nf_log_unregister(const struct nf_logger *logger)
> +void nf_log_unregister(struct nf_logger *logger)
>  {
>  	int i;
> +	struct nf_logger *llog;
>  
> -	mutex_lock(&nf_log_mutex);
> +	spin_lock_bh(&nf_log_lock);
>  	for (i = 0; i < ARRAY_SIZE(nf_loggers); i++) {
> -		if (nf_loggers[i] == logger)
> -			rcu_assign_pointer(nf_loggers[i], NULL);
> +		llog = __find_logger(i, logger->name);
> +		if (llog) {
> +			const struct nf_logger *c_logger = rcu_dereference(nf_loggers[i]);
> +			if (c_logger == llog)
> +				rcu_assign_pointer(nf_loggers[i], NULL);
> +			list_del(&(logger->list[i]));
> +		}
>  	}
> -	mutex_unlock(&nf_log_mutex);
> +	spin_unlock_bh(&nf_log_lock);
>  
>  	synchronize_rcu();
>  }
>  EXPORT_SYMBOL(nf_log_unregister);
>  
> +int nf_log_bind_pf(u_int8_t pf, const struct nf_logger *logger)
> +{
> +	if (__find_logger(pf, logger->name) == NULL)
> +		return -1;
> +
> +	spin_lock_bh(&nf_log_lock);
> +	rcu_assign_pointer(nf_loggers[pf], logger);
> +	spin_unlock_bh(&nf_log_lock);
> +	return 0;
> +}
> +EXPORT_SYMBOL(nf_log_bind_pf);
> +
> +int nf_log_unbind_pf(u_int8_t pf)
> +{
> +	spin_lock_bh(&nf_log_lock);
> +	rcu_assign_pointer(nf_loggers[pf], NULL);
> +	spin_unlock_bh(&nf_log_lock);
> +	return 0;
> +}
> +EXPORT_SYMBOL(nf_log_unbind_pf);
> +
>  void nf_log_packet(u_int8_t pf,
>  		   unsigned int hooknum,
>  		   const struct sk_buff *skb,
> @@ -163,10 +216,16 @@ static const struct file_operations nflog_file_ops = {
>  
>  int __init netfilter_log_init(void)
>  {
> +	int i;
>  #ifdef CONFIG_PROC_FS
>  	if (!proc_create("nf_log", S_IRUGO,
>  			 proc_net_netfilter, &nflog_file_ops))
>  		return -1;
>  #endif
> +
> +	for (i = NFPROTO_UNSPEC; i < NFPROTO_NUMPROTO; i++) {
> +		INIT_LIST_HEAD(&(nf_loggers_l[i]));
> +	}

Please no parens for single statements.