[PATCH 3/4] openacc: Fix asynchronous host-to-device copies in libgomp runtime

Julian Brown julian@codesourcery.com
Tue Jun 29 23:42:03 GMT 2021


This patch fixes several places in libgomp/target.c where "ephemeral" data
(on the stack or in temporary heap locations) may be used as the source of
an asynchronous host-to-device copy that may not complete before the host
data disappears.  Versions of the patch have been posted several times
before, but this one (at Chung-Lin Tang's prior suggesion, IIRC) moves
all logic into target.c rather than pushing it out to each target plugin.

An existing, but flawed, workaround for this problem in the AMD GCN
libgomp offloading plugin is currently present on mainline, and was
posted for the og9 branch here:

  https://gcc.gnu.org/legacy-ml/gcc-patches/2019-08/msg00901.html

and previous versions of this patch were posted here (for mainline/og9):

  https://gcc.gnu.org/legacy-ml/gcc-patches/2019-11/msg01482.html
  https://gcc.gnu.org/legacy-ml/gcc-patches/2019-09/msg01026.html

This patch exposes a problem with OpenACC profiling support that is
fixed by the next patch in the series. The acc_prof-parallel-1.c test
is XFAILed for now.

Tested with offloading to AMD GCN. OK?

Julian

2021-06-29  Julian Brown  <julian@codesourcery.com>

libgomp/
	* libgomp.h (gomp_copy_host2dev): Update prototype.
	(memcpy_tofrom_device, update_dev_host): Add new argument to
	gomp_copy_host2dev (false).
	* plugin/plugin-gcn.c (struct copy_data): Remove free_src field.
	(copy_data): Don't free free_src.
	(queue_push_copy): Remove free_src handling.
	(GOMP_OFFLOAD_dev2dev): Update call to queue_push_copy.
	(GOMP_OFFLOAD_openacc_async_host2dev): Remove source-data snapshotting.
	(GOMP_OFFLOAD_openacc_async_dev2host): Update call to queue_push_copy.
	* target.c (goacc_device_copy_async): Remove.
	(gomp_copy_host2dev): Add EPHEMERAL parameter. Snapshot source data
	when true, and set up deferred freeing of temporary buffer.
	(gomp_copy_dev2host): Inline device-to-host copy handling instead of
	calling goacc_device_copy_async.
	(gomp_map_vars_existing): Update calls to gomp_copy_host2dev with
	appropriate ephemeral argument.
	(gomp_map_pointer, gomp_attach_pointer, gomp_detach_pointer,
	gomp_update): Likewise.
	(gomp_map_vars_internal): Likewise. Don't use coalescing buffer for
	async copies.
	* testsuite/libgomp.oacc-c-c++-common/acc_prof-parallel-1.c: XFAIL for
	now.
---
 libgomp/libgomp.h                             |   2 +-
 libgomp/oacc-mem.c                            |   4 +-
 libgomp/plugin/plugin-gcn.c                   |  20 +---
 libgomp/target.c                              | 111 +++++++++++-------
 .../acc_prof-parallel-1.c                     |   2 +
 5 files changed, 77 insertions(+), 62 deletions(-)

diff --git a/libgomp/libgomp.h b/libgomp/libgomp.h
index 8d25dc8e2a8..e8901da1069 100644
--- a/libgomp/libgomp.h
+++ b/libgomp/libgomp.h
@@ -1226,7 +1226,7 @@ extern void gomp_acc_declare_allocate (bool, size_t, void **, size_t *,
 struct gomp_coalesce_buf;
 extern void gomp_copy_host2dev (struct gomp_device_descr *,
 				struct goacc_asyncqueue *, void *, const void *,
-				size_t, struct gomp_coalesce_buf *);
+				size_t, bool, struct gomp_coalesce_buf *);
 extern void gomp_copy_dev2host (struct gomp_device_descr *,
 				struct goacc_asyncqueue *, void *, const void *,
 				size_t);
diff --git a/libgomp/oacc-mem.c b/libgomp/oacc-mem.c
index c21508f3739..5988db0b886 100644
--- a/libgomp/oacc-mem.c
+++ b/libgomp/oacc-mem.c
@@ -202,7 +202,7 @@ memcpy_tofrom_device (bool from, void *d, void *h, size_t s, int async,
   if (from)
     gomp_copy_dev2host (thr->dev, aq, h, d, s);
   else
-    gomp_copy_host2dev (thr->dev, aq, d, h, s, /* TODO: cbuf? */ NULL);
+    gomp_copy_host2dev (thr->dev, aq, d, h, s, false, /* TODO: cbuf? */ NULL);
 
   if (profiling_p)
     {
@@ -874,7 +874,7 @@ update_dev_host (int is_dev, void *h, size_t s, int async)
   goacc_aq aq = get_goacc_asyncqueue (async);
 
   if (is_dev)
-    gomp_copy_host2dev (acc_dev, aq, d, h, s, /* TODO: cbuf? */ NULL);
+    gomp_copy_host2dev (acc_dev, aq, d, h, s, false, /* TODO: cbuf? */ NULL);
   else
     gomp_copy_dev2host (acc_dev, aq, h, d, s);
 
diff --git a/libgomp/plugin/plugin-gcn.c b/libgomp/plugin/plugin-gcn.c
index cfed42a2d4d..98da48b77cb 100644
--- a/libgomp/plugin/plugin-gcn.c
+++ b/libgomp/plugin/plugin-gcn.c
@@ -292,7 +292,6 @@ struct copy_data
   void *dst;
   const void *src;
   size_t len;
-  bool free_src;
   struct goacc_asyncqueue *aq;
 };
 
@@ -2914,8 +2913,6 @@ copy_data (void *data_)
 	     data->aq->agent->device_id, data->aq->id, data->len, data->src,
 	     data->dst);
   hsa_memory_copy_wrapper (data->dst, data->src, data->len);
-  if (data->free_src)
-    free ((void *) data->src);
   free (data);
 }
 
@@ -2934,7 +2931,7 @@ gomp_offload_free (void *ptr)
 
 static void
 queue_push_copy (struct goacc_asyncqueue *aq, void *dst, const void *src,
-		 size_t len, bool free_src)
+		 size_t len)
 {
   if (DEBUG_QUEUES)
     GCN_DEBUG ("queue_push_copy %d:%d: %zu bytes from (%p) to (%p)\n",
@@ -2944,7 +2941,6 @@ queue_push_copy (struct goacc_asyncqueue *aq, void *dst, const void *src,
   data->dst = dst;
   data->src = src;
   data->len = len;
-  data->free_src = free_src;
   data->aq = aq;
   queue_push_callback (aq, copy_data, data);
 }
@@ -3646,7 +3642,7 @@ GOMP_OFFLOAD_dev2dev (int device, void *dst, const void *src, size_t n)
     {
       struct agent_info *agent = get_agent_info (device);
       maybe_init_omp_async (agent);
-      queue_push_copy (agent->omp_async_queue, dst, src, n, false);
+      queue_push_copy (agent->omp_async_queue, dst, src, n);
       return true;
     }
 
@@ -3916,15 +3912,7 @@ GOMP_OFFLOAD_openacc_async_host2dev (int device, void *dst, const void *src,
 {
   struct agent_info *agent = get_agent_info (device);
   assert (agent == aq->agent);
-  /* The source data does not necessarily remain live until the deferred
-     copy happens.  Taking a snapshot of the data here avoids reading
-     uninitialised data later, but means that (a) data is copied twice and
-     (b) modifications to the copied data between the "spawning" point of
-     the asynchronous kernel and when it is executed will not be seen.
-     But, that is probably correct.  */
-  void *src_copy = GOMP_PLUGIN_malloc (n);
-  memcpy (src_copy, src, n);
-  queue_push_copy (aq, dst, src_copy, n, true);
+  queue_push_copy (aq, dst, src, n);
   return true;
 }
 
@@ -3936,7 +3924,7 @@ GOMP_OFFLOAD_openacc_async_dev2host (int device, void *dst, const void *src,
 {
   struct agent_info *agent = get_agent_info (device);
   assert (agent == aq->agent);
-  queue_push_copy (aq, dst, src, n, false);
+  queue_push_copy (aq, dst, src, n);
   return true;
 }
 
diff --git a/libgomp/target.c b/libgomp/target.c
index bb09d501dd6..5e4a80a67e1 100644
--- a/libgomp/target.c
+++ b/libgomp/target.c
@@ -208,22 +208,6 @@ gomp_device_copy (struct gomp_device_descr *devicep,
     }
 }
 
-static inline void
-goacc_device_copy_async (struct gomp_device_descr *devicep,
-			 bool (*copy_func) (int, void *, const void *, size_t,
-					    struct goacc_asyncqueue *),
-			 const char *dst, void *dstaddr,
-			 const char *src, const void *srcaddr,
-			 size_t size, struct goacc_asyncqueue *aq)
-{
-  if (!copy_func (devicep->target_id, dstaddr, srcaddr, size, aq))
-    {
-      gomp_mutex_unlock (&devicep->lock);
-      gomp_fatal ("Copying of %s object [%p..%p) to %s object [%p..%p) failed",
-		  src, srcaddr, srcaddr + size, dst, dstaddr, dstaddr + size);
-    }
-}
-
 /* Infrastructure for coalescing adjacent or nearly adjacent (in device addresses)
    host to device memory transfers.  */
 
@@ -317,11 +301,18 @@ gomp_to_device_kind_p (int kind)
     }
 }
 
+/* Copy host memory to an offload device.  In asynchronous mode (if AQ is
+   non-NULL), when the source data is stack or may otherwise be deallocated
+   before the asynchronous copy takes place, EPHEMERAL must be passed as
+   TRUE.  The CBUF isn't used for non-ephemeral asynchronous copies, because
+   the host data might not be computed yet (by an earlier asynchronous compute
+   region).  */
+
 attribute_hidden void
 gomp_copy_host2dev (struct gomp_device_descr *devicep,
 		    struct goacc_asyncqueue *aq,
 		    void *d, const void *h, size_t sz,
-		    struct gomp_coalesce_buf *cbuf)
+		    bool ephemeral, struct gomp_coalesce_buf *cbuf)
 {
   if (cbuf)
     {
@@ -349,8 +340,30 @@ gomp_copy_host2dev (struct gomp_device_descr *devicep,
 	}
     }
   if (__builtin_expect (aq != NULL, 0))
-    goacc_device_copy_async (devicep, devicep->openacc.async.host2dev_func,
-			     "dev", d, "host", h, sz, aq);
+    {
+      void *srcdata = (void *) h;
+      if (ephemeral)
+	{
+	  /* We're queueing up an asynchronous copy from data that may
+	     disappear before the transfer takes place (i.e. because it is a
+	     stack local in a function that is no longer executing).  Make a
+	     copy of the data into a temporary buffer in those cases.  */
+	  void *tmpbuf = gomp_malloc (sz);
+	  memcpy (tmpbuf, h, sz);
+	  srcdata = tmpbuf;
+	}
+      if (!devicep->openacc.async.host2dev_func (devicep->target_id, d,
+						 srcdata, sz, aq))
+	{
+	  gomp_mutex_unlock (&devicep->lock);
+	  gomp_fatal ("Copying of host object [%p..%p) to dev object [%p..%p) "
+		      "failed", h, h + sz, d, d + sz);
+	}
+      /* Free any temporary buffer created above once the transfer has
+	 completed.  */
+      if (srcdata != h)
+	devicep->openacc.async.queue_callback_func (aq, free, srcdata);
+    }
   else
     gomp_device_copy (devicep, devicep->host2dev_func, "dev", d, "host", h, sz);
 }
@@ -361,8 +374,15 @@ gomp_copy_dev2host (struct gomp_device_descr *devicep,
 		    void *h, const void *d, size_t sz)
 {
   if (__builtin_expect (aq != NULL, 0))
-    goacc_device_copy_async (devicep, devicep->openacc.async.dev2host_func,
-			     "host", h, "dev", d, sz, aq);
+    {
+      if (!devicep->openacc.async.dev2host_func (devicep->target_id, h, d, sz,
+						 aq))
+	{
+	  gomp_mutex_unlock (&devicep->lock);
+	  gomp_fatal ("Copying of dev object [%p..%p) to host object [%p..%p) "
+		      "failed", d, d + sz, h, h + sz);
+	}
+    }
   else
     gomp_device_copy (devicep, devicep->dev2host_func, "host", h, "dev", d, sz);
 }
@@ -521,7 +541,7 @@ gomp_map_vars_existing (struct gomp_device_descr *devicep,
 			(void *) (oldn->tgt->tgt_start + oldn->tgt_offset
 				  + newn->host_start - oldn->host_start),
 			(void *) newn->host_start,
-			newn->host_end - newn->host_start, cbuf);
+			newn->host_end - newn->host_start, false, cbuf);
 
   gomp_increment_refcount (oldn, refcount_set);
 }
@@ -548,8 +568,8 @@ gomp_map_pointer (struct target_mem_desc *tgt, struct goacc_asyncqueue *aq,
       cur_node.tgt_offset = (uintptr_t) NULL;
       gomp_copy_host2dev (devicep, aq,
 			  (void *) (tgt->tgt_start + target_offset),
-			  (void *) &cur_node.tgt_offset,
-			  sizeof (void *), cbuf);
+			  (void *) &cur_node.tgt_offset, sizeof (void *),
+			  true, cbuf);
       return;
     }
   /* Add bias to the pointer value.  */
@@ -569,7 +589,8 @@ gomp_map_pointer (struct target_mem_desc *tgt, struct goacc_asyncqueue *aq,
      to initialize the pointer with.  */
   cur_node.tgt_offset -= bias;
   gomp_copy_host2dev (devicep, aq, (void *) (tgt->tgt_start + target_offset),
-		      (void *) &cur_node.tgt_offset, sizeof (void *), cbuf);
+		      (void *) &cur_node.tgt_offset, sizeof (void *), true,
+		      cbuf);
 }
 
 static void
@@ -702,7 +723,7 @@ gomp_attach_pointer (struct gomp_device_descr *devicep,
 		  (void *) (n->tgt->tgt_start + n->tgt_offset), (void *) data);
 
       gomp_copy_host2dev (devicep, aq, (void *) devptr, (void *) &data,
-			  sizeof (void *), cbufp);
+			  sizeof (void *), true, cbufp);
     }
   else
     gomp_debug (1, "%s: attach count for %p -> %u\n", __FUNCTION__,
@@ -755,7 +776,7 @@ gomp_detach_pointer (struct gomp_device_descr *devicep,
 		  (void *) target);
 
       gomp_copy_host2dev (devicep, aq, (void *) devptr, (void *) &target,
-			  sizeof (void *), cbufp);
+			  sizeof (void *), true, cbufp);
     }
   else
     gomp_debug (1, "%s: attach count for %p -> %u\n", __FUNCTION__,
@@ -927,8 +948,9 @@ gomp_map_vars_internal (struct gomp_device_descr *devicep,
 	      for (i = first; i <= last; i++)
 		{
 		  tgt->list[i].key = NULL;
-		  if (gomp_to_device_kind_p (get_kind (short_mapkind, kinds, i)
-					     & typemask))
+		  if (!aq
+		      && gomp_to_device_kind_p (get_kind (short_mapkind, kinds,
+							  i) & typemask))
 		    gomp_coalesce_buf_add (&cbuf,
 					   tgt_size - cur_node.host_end
 					   + (uintptr_t) hostaddrs[i],
@@ -969,8 +991,9 @@ gomp_map_vars_internal (struct gomp_device_descr *devicep,
 	  if (tgt_align < align)
 	    tgt_align = align;
 	  tgt_size = (tgt_size + align - 1) & ~(align - 1);
-	  gomp_coalesce_buf_add (&cbuf, tgt_size,
-				 cur_node.host_end - cur_node.host_start);
+	  if (!aq)
+	    gomp_coalesce_buf_add (&cbuf, tgt_size,
+				   cur_node.host_end - cur_node.host_start);
 	  tgt_size += cur_node.host_end - cur_node.host_start;
 	  has_firstprivate = true;
 	  continue;
@@ -1063,7 +1086,7 @@ gomp_map_vars_internal (struct gomp_device_descr *devicep,
 	  if (tgt_align < align)
 	    tgt_align = align;
 	  tgt_size = (tgt_size + align - 1) & ~(align - 1);
-	  if (gomp_to_device_kind_p (kind & typemask))
+	  if (!aq && gomp_to_device_kind_p (kind & typemask))
 	    gomp_coalesce_buf_add (&cbuf, tgt_size,
 				   cur_node.host_end - cur_node.host_start);
 	  tgt_size += cur_node.host_end - cur_node.host_start;
@@ -1218,7 +1241,7 @@ gomp_map_vars_internal (struct gomp_device_descr *devicep,
 		len = sizes[i];
 		gomp_copy_host2dev (devicep, aq,
 				    (void *) (tgt->tgt_start + tgt_size),
-				    (void *) hostaddrs[i], len, cbufp);
+				    (void *) hostaddrs[i], len, false, cbufp);
 		tgt_size += len;
 		continue;
 	      case GOMP_MAP_FIRSTPRIVATE_INT:
@@ -1307,12 +1330,11 @@ gomp_map_vars_internal (struct gomp_device_descr *devicep,
 		if (cur_node.tgt_offset)
 		  cur_node.tgt_offset -= sizes[i];
 		gomp_copy_host2dev (devicep, aq,
-				    (void *) (n->tgt->tgt_start
-					      + n->tgt_offset
+				    (void *) (n->tgt->tgt_start + n->tgt_offset
 					      + cur_node.host_start
 					      - n->host_start),
 				    (void *) &cur_node.tgt_offset,
-				    sizeof (void *), cbufp);
+				    sizeof (void *), true, cbufp);
 		cur_node.tgt_offset = n->tgt->tgt_start + n->tgt_offset
 				      + cur_node.host_start - n->host_start;
 		continue;
@@ -1450,7 +1472,8 @@ gomp_map_vars_internal (struct gomp_device_descr *devicep,
 					(void *) (tgt->tgt_start
 						  + k->tgt_offset),
 					(void *) k->host_start,
-					k->host_end - k->host_start, cbufp);
+					k->host_end - k->host_start, false,
+					cbufp);
 		    break;
 		  case GOMP_MAP_POINTER:
 		    gomp_map_pointer (tgt, aq,
@@ -1462,7 +1485,8 @@ gomp_map_vars_internal (struct gomp_device_descr *devicep,
 					(void *) (tgt->tgt_start
 						  + k->tgt_offset),
 					(void *) k->host_start,
-					k->host_end - k->host_start, cbufp);
+					k->host_end - k->host_start, false,
+					cbufp);
 		    tgt->list[i].has_null_ptr_assoc = false;
 
 		    for (j = i + 1; j < mapnum; j++)
@@ -1525,7 +1549,7 @@ gomp_map_vars_internal (struct gomp_device_descr *devicep,
 					(void *) (tgt->tgt_start
 						  + k->tgt_offset),
 					(void *) k->host_start,
-					sizeof (void *), cbufp);
+					sizeof (void *), false, cbufp);
 		    break;
 		  default:
 		    gomp_mutex_unlock (&devicep->lock);
@@ -1541,7 +1565,7 @@ gomp_map_vars_internal (struct gomp_device_descr *devicep,
 		    /* We intentionally do not use coalescing here, as it's not
 		       data allocated by the current call to this function.  */
 		    gomp_copy_host2dev (devicep, aq, (void *) n->tgt_offset,
-					&tgt_addr, sizeof (void *), NULL);
+					&tgt_addr, sizeof (void *), true, NULL);
 		  }
 		array++;
 	      }
@@ -1556,7 +1580,7 @@ gomp_map_vars_internal (struct gomp_device_descr *devicep,
 	  gomp_copy_host2dev (devicep, aq,
 			      (void *) (tgt->tgt_start + i * sizeof (void *)),
 			      (void *) &cur_node.tgt_offset, sizeof (void *),
-			      cbufp);
+			      true, cbufp);
 	}
     }
 
@@ -1568,7 +1592,8 @@ gomp_map_vars_internal (struct gomp_device_descr *devicep,
 			    (void *) (tgt->tgt_start + cbuf.chunks[c].start),
 			    (char *) cbuf.buf + (cbuf.chunks[c].start
 						 - cbuf.chunks[0].start),
-			    cbuf.chunks[c].end - cbuf.chunks[c].start, NULL);
+			    cbuf.chunks[c].end - cbuf.chunks[c].start, true,
+			    NULL);
       free (cbuf.buf);
       cbuf.buf = NULL;
       cbufp = NULL;
@@ -1892,7 +1917,7 @@ gomp_update (struct gomp_device_descr *devicep, size_t mapnum, void **hostaddrs,
 
 	    if (GOMP_MAP_COPY_TO_P (kind & typemask))
 	      gomp_copy_host2dev (devicep, NULL, devaddr, hostaddr, size,
-				  NULL);
+				  false, NULL);
 	    if (GOMP_MAP_COPY_FROM_P (kind & typemask))
 	      gomp_copy_dev2host (devicep, NULL, hostaddr, devaddr, size);
 	  }
diff --git a/libgomp/testsuite/libgomp.oacc-c-c++-common/acc_prof-parallel-1.c b/libgomp/testsuite/libgomp.oacc-c-c++-common/acc_prof-parallel-1.c
index a5e9ab3f936..dc1807c6ce4 100644
--- a/libgomp/testsuite/libgomp.oacc-c-c++-common/acc_prof-parallel-1.c
+++ b/libgomp/testsuite/libgomp.oacc-c-c++-common/acc_prof-parallel-1.c
@@ -1,3 +1,5 @@
+/* { dg-xfail-run-if "Async profiling bug" { *-*-* } } */
+
 /* Test dispatch of events to callbacks.  */
 
 #undef NDEBUG
-- 
2.29.2



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