Subject: Re: [PATCH net 3/3] sctp: remove the dead field of sctp_transport

From: Marcelo Ricardo Leitner <[email-masked]>
Date: Thu, 21 Jan 2016 15:54:38 -0200

On Fri, Jan 22, 2016 at 01:49:09AM +0800, Xin Long wrote:
> After we use refcnt to check if transport is alive, the dead can be
> removed from sctp_transport.
> 
> The traversal of transport_addr_list in procfs dump is using
> list_for_each_entry_rcu, no need to check if it has been freed.
> 
> sctp_generate_t3_rtx_event and sctp_generate_heartbeat_event is
> protected by sock lock, it's not necessary to check dead, either.
> also, the timers are cancelled when sctp_transport_free() is
> called, that it doesn't wait for refcnt to reach 0 to cancel them.
> 
> Signed-off-by: Xin Long <[email-masked]>

Signed-off-by: Marcelo Ricardo Leitner <[email-masked]>

> ---
>  include/net/sctp/structs.h |  3 +--
>  net/sctp/proc.c            |  4 ----
>  net/sctp/sm_sideeffect.c   | 12 ------------
>  net/sctp/transport.c       |  4 +---
>  4 files changed, 2 insertions(+), 21 deletions(-)
> 
> diff --git a/include/net/sctp/structs.h b/include/net/sctp/structs.h
> index 344da04..205630b 100644
> --- a/include/net/sctp/structs.h
> +++ b/include/net/sctp/structs.h
> @@ -756,7 +756,6 @@ struct sctp_transport {
>  
>  	/* Reference counting. */
>  	atomic_t refcnt;
> -	__u32	 dead:1,
>  		/* RTO-Pending : A flag used to track if one of the DATA
>  		 *		chunks sent to this address is currently being
>  		 *		used to compute a RTT. If this flag is 0,
> @@ -766,7 +765,7 @@ struct sctp_transport {
>  		 *		calculation completes (i.e. the DATA chunk
>  		 *		is SACK'd) clear this flag.
>  		 */
> -		 rto_pending:1,
> +	__u32	rto_pending:1,
>  
>  		/*
>  		 * hb_sent : a flag that signals that we have a pending
> diff --git a/net/sctp/proc.c b/net/sctp/proc.c
> index c74a810..ded7d93 100644
> --- a/net/sctp/proc.c
> +++ b/net/sctp/proc.c
> @@ -165,8 +165,6 @@ static void sctp_seq_dump_remote_addrs(struct seq_file *seq, struct sctp_associa
>  	list_for_each_entry_rcu(transport, &assoc->peer.transport_addr_list,
>  			transports) {
>  		addr = &transport->ipaddr;
> -		if (transport->dead)
> -			continue;
>  
>  		af = sctp_get_af_specific(addr->sa.sa_family);
>  		if (af->cmp_addr(addr, primary)) {
> @@ -499,8 +497,6 @@ static int sctp_remaddr_seq_show(struct seq_file *seq, void *v)
>  
>  	list_for_each_entry_rcu(tsp, &assoc->peer.transport_addr_list,
>  				transports) {
> -		if (tsp->dead)
> -			continue;
>  		/*
>  		 * The remote address (ADDR)
>  		 */
> diff --git a/net/sctp/sm_sideeffect.c b/net/sctp/sm_sideeffect.c
> index 2e21384..b5327bb 100644
> --- a/net/sctp/sm_sideeffect.c
> +++ b/net/sctp/sm_sideeffect.c
> @@ -259,12 +259,6 @@ void sctp_generate_t3_rtx_event(unsigned long peer)
>  		goto out_unlock;
>  	}
>  
> -	/* Is this transport really dead and just waiting around for
> -	 * the timer to let go of the reference?
> -	 */
> -	if (transport->dead)
> -		goto out_unlock;
> -
>  	/* Run through the state machine.  */
>  	error = sctp_do_sm(net, SCTP_EVENT_T_TIMEOUT,
>  			   SCTP_ST_TIMEOUT(SCTP_EVENT_TIMEOUT_T3_RTX),
> @@ -380,12 +374,6 @@ void sctp_generate_heartbeat_event(unsigned long data)
>  		goto out_unlock;
>  	}
>  
> -	/* Is this structure just waiting around for us to actually
> -	 * get destroyed?
> -	 */
> -	if (transport->dead)
> -		goto out_unlock;
> -
>  	error = sctp_do_sm(net, SCTP_EVENT_T_TIMEOUT,
>  			   SCTP_ST_TIMEOUT(SCTP_EVENT_TIMEOUT_HEARTBEAT),
>  			   asoc->state, asoc->ep, asoc,
> diff --git a/net/sctp/transport.c b/net/sctp/transport.c
> index 69f3799..a431c14 100644
> --- a/net/sctp/transport.c
> +++ b/net/sctp/transport.c
> @@ -132,8 +132,6 @@ fail:
>   */
>  void sctp_transport_free(struct sctp_transport *transport)
>  {
> -	transport->dead = 1;
> -
>  	/* Try to delete the heartbeat timer.  */
>  	if (del_timer(&transport->hb_timer))
>  		sctp_transport_put(transport);
> @@ -169,7 +167,7 @@ static void sctp_transport_destroy_rcu(struct rcu_head *head)
>   */
>  static void sctp_transport_destroy(struct sctp_transport *transport)
>  {
> -	if (unlikely(!transport->dead)) {
> +	if (unlikely(atomic_read(&transport->refcnt))) {
>  		WARN(1, "Attempt to destroy undead transport %p!\n", transport);
>  		return;
>  	}
> -- 
> 2.1.0
> 
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