Date:	Mon, 25 Aug 2014 21:17:31 +0000
From:	Jon Maloy <jon.maloy@...csson.com>
To:	Erik Hugne <erik.hugne@...csson.com>,
	"ying.xue@...driver.com" <ying.xue@...driver.com>,
	Richard Alpe <richard.alpe@...csson.com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
CC:	"tipc-discussion@...ts.sourceforge.net" 
	<tipc-discussion@...ts.sourceforge.net>
Subject: RE: [PATCH net-next 2/2] tipc: add name distributor resiliency queue



> -----Original Message-----
> From: Erik Hugne
> Sent: August-25-14 10:54 AM
> To: Jon Maloy; ying.xue@...driver.com; Richard Alpe;
> netdev@...r.kernel.org
> Cc: tipc-discussion@...ts.sourceforge.net; Erik Hugne
> Subject: [PATCH net-next 2/2] tipc: add name distributor resiliency queue
> 
> From: Erik Hugne <erik.hugne@...csson.com>
> 
> TIPC name table updates are distributed asynchronously in a cluster, entailing
> a risk of certain race conditions. E.g., if two nodes simultaneously issue
> conflicting (overlapping) publications, this may not be detected until both
> publications have reached a third node, in which case one of the publications
> will be silently dropped on that node. Hence, we end up with an inconsistent
> name table.
> 
> In most cases this conflict is just a temporary race, e.g., one node is issuing a
> publication under the assumption that a previous, conflicting, publication has
> already been withdrawn by the other node.
> However, because of the (rtt related) distributed update delay, this may not
> yet hold true on all nodes. The symptom of this failure is a syslog message:
> "tipc: Cannot publish {%u,%u,%u}, overlap error".
> 
> In this commit we add a resiliency queue at the receiving end of the name
> table distributor. When insertion of an arriving publication fails, we retain it in
> this queue for a short amount of time, assuming that another update will
> arrive very soon and clear the conflict. If so happens, we insert the
> publication, otherwise we drop it.
> 
> The (configurable) retention value defaults to 2000 ms. Knowing from
> experience that the situation described above is extremely rare, there is no
> risk that the queue will accumulate any large number of items.
> 
> Signed-off-by: Erik Hugne <erik.hugne@...csson.com>
> Signed-off-by: Jon Maloy <jon.maloy@...csson.com>
> ---
>  Documentation/sysctl/net.txt | 14 +++++++++
>  net/tipc/core.h              |  1 +
>  net/tipc/name_distr.c        | 69
> ++++++++++++++++++++++++++++++++++++++++++--
>  net/tipc/name_distr.h        |  1 +
>  net/tipc/name_table.c        |  8 ++---
>  net/tipc/sysctl.c            |  7 +++++
>  6 files changed, 93 insertions(+), 7 deletions(-)
> 
> diff --git a/Documentation/sysctl/net.txt b/Documentation/sysctl/net.txt
> index 9a0319a..89ce54e 100644
> --- a/Documentation/sysctl/net.txt
> +++ b/Documentation/sysctl/net.txt
> @@ -241,6 +241,9 @@ address of the router (or Connected) for internal
> networks.
>  6. TIPC
>  -------------------------------------------------------
> 
> +tipc_rmem
> +----------
> +
>  The TIPC protocol now has a tunable for the receive memory, similar to the
> tcp_rmem - i.e. a vector of 3 INTEGERs: (min, default, max)
> 
> @@ -252,3 +255,14 @@ The max value is set to CONN_OVERLOAD_LIMIT,
> and the default and min values  are scaled (shifted) versions of that same
> value.  Note that the min value  is not at this point in time used in any
> meaningful way, but the triplet is  preserved in order to be consistent with
> things like tcp_rmem.
> +
> +named_timeout
> +--------------
> +
> +TIPC name table updates are distributed asynchronous

asynchronously

>+ in a cluster,
without any form of transaction handling.

This means that different race scenarios are possible.  One such is that
a  name withdrawal sent out by one node and received by a another node
may arrive after a second, overlapping name publication already has been
accepted from a third node, although the conflicting updates originally may
have been  issued in the correct sequential order.

> +If named_timeout is nonzero, failed topology updates will be placed on
> +a defer queue until another event arrives that clears the error, or
> +until the timeout expires. Value is in milliseconds.
> diff --git a/net/tipc/core.h b/net/tipc/core.h index d2607a8..f773b14 100644
> --- a/net/tipc/core.h
> +++ b/net/tipc/core.h
> @@ -81,6 +81,7 @@ extern u32 tipc_own_addr __read_mostly;  extern int
> tipc_max_ports __read_mostly;  extern int tipc_net_id __read_mostly;
> extern int sysctl_tipc_rmem[3] __read_mostly;
> +extern int sysctl_tipc_named_timeout __read_mostly;
> 
>  /*
>   * Other global variables
> diff --git a/net/tipc/name_distr.c b/net/tipc/name_distr.c index
> 0591f33..0cbe5e1 100644
> --- a/net/tipc/name_distr.c
> +++ b/net/tipc/name_distr.c
> @@ -1,7 +1,7 @@
>  /*
>   * net/tipc/name_distr.c: TIPC name distribution code
>   *
> - * Copyright (c) 2000-2006, Ericsson AB
> + * Copyright (c) 2000-2006, 2014, Ericsson AB
>   * Copyright (c) 2005, 2010-2011, Wind River Systems
>   * All rights reserved.
>   *
> @@ -71,6 +71,21 @@ static struct publ_list *publ_lists[] = {  };
> 
> 
> +int sysctl_tipc_named_timeout __read_mostly = 2000;
> +
> +/**
> + * struct tipc_dist_queue - queue holding deferred name table updates
> +*/ static struct list_head tipc_dist_queue =
> +LIST_HEAD_INIT(tipc_dist_queue);
> +
> +struct distr_queue_item {
> +	struct distr_item i;
> +	u32 dtype;
> +	u32 node;
> +	u64 expiry;
> +	struct list_head next;
> +};
> +
>  /**
>   * publ_to_item - add publication info to a publication message
>   */
> @@ -299,6 +314,52 @@ struct publication *tipc_update_nametbl(struct
> distr_item *i, u32 node,  }
> 
>  /**
> + * tipc_named_add_backlog - add a failed name table update to the
> +backlog
> + *
> + */
> +static void tipc_named_add_backlog(struct distr_item *i, u32 type, u32
> +node) {
> +	struct distr_queue_item *e;
> +	u64 now = get_jiffies_64();
> +
> +	e = kzalloc(sizeof(*e), GFP_ATOMIC);
> +	if (!e)
> +		return;
> +	e->dtype = type;
> +	e->node = node;
> +	e->expiry = now + msecs_to_jiffies(sysctl_tipc_named_timeout);
> +	memcpy(e, i, sizeof(*i));
> +	list_add_tail(&e->next, &tipc_dist_queue); }
> +
> +/**
> + * tipc_named_process_backlog - try to process any pending name table
> +updates
> + * from the network.
> + */
> +void tipc_named_process_backlog(void)
> +{
> +	struct distr_queue_item *e, *tmp;
> +	char addr[16];
> +	u64 now = get_jiffies_64();
> +
> +	list_for_each_entry_safe(e, tmp, &tipc_dist_queue, next) {
> +		if (e->expiry > now) {
> +			if (!tipc_update_nametbl(&e->i, e->node, e-
> >dtype))
> +				continue;
> +		} else {
> +			tipc_addr_string_fill(addr, e->node);
> +			pr_warn_ratelimited("Dropping name table update
> (%d) of {%u, %u, %u} from %s key=%u\n",
> +					    e->dtype, ntohl(e->i.type),
> +					    ntohl(e->i.lower),
> +					    ntohl(e->i.upper),

 
+                                                                                 tipc_addr_string_fill(addr),

Otherwise you'll have a nice little crash here ;)

Apart from this I am ok with it. You can add "Reviewed-by"  from me.

///jon


> +                                                                            ntohl(e->i.key));
> +		}
> +		list_del(&e->next);
> +		kfree(e);
> +	}
> +}
> +
> +/**
>   * tipc_named_rcv - process name table update message sent by another
> node
>   */
>  void tipc_named_rcv(struct sk_buff *buf) @@ -306,13 +367,15 @@ void
> tipc_named_rcv(struct sk_buff *buf)
>  	struct tipc_msg *msg = buf_msg(buf);
>  	struct distr_item *item = (struct distr_item *)msg_data(msg);
>  	u32 count = msg_data_sz(msg) / ITEM_SIZE;
> +	u32 node = msg_orignode(msg);
> 
>  	write_lock_bh(&tipc_nametbl_lock);
>  	while (count--) {
> -		tipc_update_nametbl(item, msg_orignode(msg),
> -				    msg_type(msg));
> +		if (!tipc_update_nametbl(item, node, msg_type(msg)))
> +			tipc_named_add_backlog(item, msg_type(msg),
> node);
>  		item++;
>  	}
> +	tipc_named_process_backlog();
>  	write_unlock_bh(&tipc_nametbl_lock);
>  	kfree_skb(buf);
>  }
> diff --git a/net/tipc/name_distr.h b/net/tipc/name_distr.h index
> 8afe32b..b9e75fe 100644
> --- a/net/tipc/name_distr.h
> +++ b/net/tipc/name_distr.h
> @@ -73,5 +73,6 @@ void named_cluster_distribute(struct sk_buff *buf);
> void tipc_named_node_up(u32 dnode);  void tipc_named_rcv(struct sk_buff
> *buf);  void tipc_named_reinit(void);
> +void tipc_named_process_backlog(void);
> 
>  #endif
> diff --git a/net/tipc/name_table.c b/net/tipc/name_table.c index
> c058e30..3a6a0a7 100644
> --- a/net/tipc/name_table.c
> +++ b/net/tipc/name_table.c
> @@ -261,8 +261,6 @@ static struct publication
> *tipc_nameseq_insert_publ(struct name_seq *nseq,
> 
>  		/* Lower end overlaps existing entry => need an exact match
> */
>  		if ((sseq->lower != lower) || (sseq->upper != upper)) {
> -			pr_warn("Cannot publish {%u,%u,%u}, overlap
> error\n",
> -				type, lower, upper);
>  			return NULL;
>  		}
> 
> @@ -284,8 +282,6 @@ static struct publication
> *tipc_nameseq_insert_publ(struct name_seq *nseq,
>  		/* Fail if upper end overlaps into an existing entry */
>  		if ((inspos < nseq->first_free) &&
>  		    (upper >= nseq->sseqs[inspos].lower)) {
> -			pr_warn("Cannot publish {%u,%u,%u}, overlap
> error\n",
> -				type, lower, upper);
>  			return NULL;
>  		}
> 
> @@ -677,6 +673,8 @@ struct publication *tipc_nametbl_publish(u32 type,
> u32 lower, u32 upper,
>  	if (likely(publ)) {
>  		table.local_publ_count++;
>  		buf = tipc_named_publish(publ);
> +		/* Any pending external events? */
> +		tipc_named_process_backlog();
>  	}
>  	write_unlock_bh(&tipc_nametbl_lock);
> 
> @@ -698,6 +696,8 @@ int tipc_nametbl_withdraw(u32 type, u32 lower, u32
> ref, u32 key)
>  	if (likely(publ)) {
>  		table.local_publ_count--;
>  		buf = tipc_named_withdraw(publ);
> +		/* Any pending external events? */
> +		tipc_named_process_backlog();
>  		write_unlock_bh(&tipc_nametbl_lock);
>  		list_del_init(&publ->pport_list);
>  		kfree(publ);
> diff --git a/net/tipc/sysctl.c b/net/tipc/sysctl.c index f3fef93..1a779b1 100644
> --- a/net/tipc/sysctl.c
> +++ b/net/tipc/sysctl.c
> @@ -47,6 +47,13 @@ static struct ctl_table tipc_table[] = {
>  		.mode		= 0644,
>  		.proc_handler	= proc_dointvec,
>  	},
> +	{
> +		.procname	= "named_timeout",
> +		.data		= &sysctl_tipc_named_timeout,
> +		.maxlen		=
> sizeof(sysctl_tipc_named_timeout),
> +		.mode		= 0644,
> +		.proc_handler	= proc_dointvec,
> +	},
>  	{}
>  };
> 
> --
> 1.8.3.2

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