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

Hal Rosenstock
2010-04-19T18:20:56Z

On Mon, Apr 19, 2010 at 5:15 AM, Line Holen <Line.Holen-xsfywfwIY+M@public.gmane.org> 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

To me, this begs the question of whether this should return a BUSY
status rather than no record (and whether SA clients should handle
those two differently) but that is a bigger change (and may require
some end node change as well).

Also, should a similar change be made in SA MPR mpr_rcv_get_path_parms ?

-- Hal

> 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>
>
> ---
>
> 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
> +
>  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;
> +               }
>        }
>
>        /*
> --
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