Re: [PATCH] opensm/osm_sa_path_record.c: livelock in pr_rcv_get_path_parms

Sasha Khapyorsky
2010-04-19T15:34:21Z

On 11:15 Mon 19 Apr , Line Holen wrote:
> SA path request handling can end up in a livelock in pr_rcv_get_path_parms().
> This can happen if a path request is handled while LFT updates to the fabric
> are in progress.
> The LFT of the switch data structure is updated as part of the LFT response
> processing. So while the SM is busy pushing the LFT updates, some switches have
> up to date LFT info while others are not yet updated and contains the LFT of
> the previous routing. For a (short) time interval there is a potential for
> loops in the fabric. The livelock occurs if a path request is received during
> this time interval.
> Both LFT response handling and path request processing needs the SM lock.
> When the livelock occurs the LFT response handling blocks forever waiting for
> the lock to be released.
>
> The suggested fix is simply to introduce a max number of hops that should
> be traversed while handling the path request. If this max is reached then
> the request will return with NO_RECORD response and release the SM lock.
> This way the LFT processing will be able to complete.
>
> Signed-off-by: Line Holen <Line.Holen-xsfywfwIY+M@public.gmane.org>

Applied. Thanks. See minor question/note below.

>
> ---
>
> diff --git a/opensm/opensm/osm_sa_path_record.c b/opensm/opensm/osm_sa_path_record.c
> index c4c3f86..b399b70 100644
> --- a/opensm/opensm/osm_sa_path_record.c
> +++ b/opensm/opensm/osm_sa_path_record.c
> @@ -4,6 +4,7 @@
> * Copyright (c) 1996-2003 Intel Corporation. All rights reserved.
> * Copyright (c) 2008 Xsigo Systems Inc. All rights reserved.
> * Copyright (c) 2009 HNR Consulting. All rights reserved.
> + * Copyright (c) 2010 Sun Microsystems, Inc. All rights reserved.
> *
> * This software is available to you under a choice of one of two
> * licenses. You may choose to be licensed under the terms of the GNU
> @@ -69,6 +70,9 @@
> #include <opensm/osm_prefix_route.h>
> #include <opensm/osm_ucast_lash.h>
>
> +
> +#define MAX_HOPS 128

IB spec defines maximal number of hops for a fabric which is 64. Would
it be netter to use this value here?

Sasha

> +
> typedef struct osm_pr_item {
> cl_list_item_t list_item;
> ib_path_rec_t path_rec;
> @@ -178,6 +182,7 @@ static ib_api_status_t pr_rcv_get_path_parms(IN osm_sa_t * sa,
> osm_qos_level_t *p_qos_level = NULL;
> uint16_t valid_sl_mask = 0xffff;
> int is_lash;
> + int hops = 0;
>
> OSM_LOG_ENTER(sa->p_log);
>
> @@ -369,6 +374,25 @@ static ib_api_status_t pr_rcv_get_path_parms(IN osm_sa_t * sa,
> goto Exit;
> }
> }
> +
> + /* update number of hops traversed */
> + hops++;
> + if (hops > MAX_HOPS) {
> +
> + OSM_LOG(sa->p_log, OSM_LOG_ERROR,
> + "Path from GUID 0x%016" PRIx64 " (%s) to lid %u GUID 0x%016"
> + PRIx64 " (%s) needs more than %d hops, "
> + "max %d hops allowed\n",
> + cl_ntoh64(osm_physp_get_port_guid(p_src_physp)),
> + p_src_physp->p_node->print_desc,
> + dest_lid_ho,
> + cl_ntoh64(osm_physp_get_port_guid(p_dest_physp)),
> + p_dest_physp->p_node->print_desc,
> + hops, MAX_HOPS);
> +
> + status = IB_NOT_FOUND;
> + goto Exit;
> + }
> }
>
> /*