[PATCH 02/13] OpenACC reference count overhaul

[Thomas Schwinge]

Hi Julian!

On 2019-12-17T22:02:27-0800, Julian Brown <julian@codesourcery.com> wrote:
> --- a/libgomp/oacc-mem.c
> +++ b/libgomp/oacc-mem.c

> @@ -571,14 +570,16 @@ present_create_copy (unsigned f, void *h, size_t s, int async)
>
>        goacc_aq aq = get_goacc_asyncqueue (async);
>
> -      tgt = gomp_map_vars_async (acc_dev, aq, mapnum, &hostaddrs, NULL, &s,
> -                              &kinds, true, GOMP_MAP_VARS_OPENACC);
> -      n = tgt->list[0].key;
> -      assert (n->refcount == 1);
> -      assert (n->dynamic_refcount == 0);
> -      n->dynamic_refcount++;
> +      gomp_map_vars_async (acc_dev, aq, mapnum, &hostaddrs, NULL, &s, &kinds,
> +                        true, GOMP_MAP_VARS_OPENACC_ENTER_DATA);
>
> -      d = tgt->to_free;
> +      gomp_mutex_lock (&acc_dev->lock);
> +      n = lookup_host (acc_dev, h, s);
> +      assert (n != NULL);
> +      assert (n->tgt_offset == 0);
> +      assert ((uintptr_t) h == n->host_start);
> +      d = (void *) n->tgt->tgt_start;
> +      gomp_mutex_unlock (&acc_dev->lock);
>      }

Notwithstanding the open question of the "'gomp_map_vars' locking
protocol" (discussed in a different thread, to be resolved
independently), is there a reason that you changed this code to look up
'n = lookup_host ([...])'?  This is the case that 'gomp_map_vars' enters
a new mapping, so by construction, 'n = tgt->list[0].key' must hold?  I
tested the following:

    --- libgomp/oacc-mem.c
    +++ libgomp/oacc-mem.c
    @@ -555,16 +555,17 @@ goacc_enter_datum (void **hostaddrs, size_t *sizes, void *kinds, int async)

           goacc_aq aq = get_goacc_asyncqueue (async);

    -      gomp_map_vars_async (acc_dev, aq, mapnum, hostaddrs, NULL, sizes, kinds,
    -                      true, GOMP_MAP_VARS_OPENACC_ENTER_DATA);
    +      struct target_mem_desc *tgt
    +   = gomp_map_vars_async (acc_dev, aq, mapnum, hostaddrs, NULL, sizes, kinds,
    +                          true, GOMP_MAP_VARS_OPENACC_ENTER_DATA);
    +      assert (tgt);
    +      n = tgt->list[0].key;
    +      assert (n->refcount == 1);
    +      assert (n->virtual_refcount == 0);

    -      gomp_mutex_lock (&acc_dev->lock);
    -      n = lookup_host (acc_dev, hostaddrs[0], sizes[0]);
    -      assert (n != NULL);
           assert (n->tgt_offset == 0);
           assert ((uintptr_t) hostaddrs[0] == n->host_start);
           d = (void *) n->tgt->tgt_start;
    -      gomp_mutex_unlock (&acc_dev->lock);
         }

..., and don't see any regressions.  If approving this patch, please
respond with "Reviewed-by: NAME <EMAIL>" so that your effort will be
recorded in the commit log, see <https://gcc.gnu.org/wiki/Reviewed-by>.


Grüße
 Thomas
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