[src/trunk]: src/sys/external/bsd/drm2/linux Judiciously insert __insn_barrie...

[riastradh <riastradh%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/b9fdd34b513c
branches:  trunk
changeset: 1028095:b9fdd34b513c
user:      riastradh <riastradh%NetBSD.org@localhost>
date:      Sun Dec 19 01:50:25 2021 +0000

description:
Judiciously insert __insn_barrier into reservation logic.

Nothing is volatile here, so we must handle the barriers ourselves.

Also note where membar_producer is implied.

diffstat:

 sys/external/bsd/drm2/linux/linux_reservation.c |  62 +++++++++++++++++++-----
 1 files changed, 48 insertions(+), 14 deletions(-)

diffs (177 lines):

diff -r 7a8a568633dc -r b9fdd34b513c sys/external/bsd/drm2/linux/linux_reservation.c
--- a/sys/external/bsd/drm2/linux/linux_reservation.c   Sun Dec 19 01:50:17 2021 +0000
+++ b/sys/external/bsd/drm2/linux/linux_reservation.c   Sun Dec 19 01:50:25 2021 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: linux_reservation.c,v 1.22 2021/12/19 01:50:18 riastradh Exp $ */
+/*     $NetBSD: linux_reservation.c,v 1.23 2021/12/19 01:50:25 riastradh Exp $ */
 
 /*-
  * Copyright (c) 2018 The NetBSD Foundation, Inc.
@@ -30,7 +30,7 @@
  */
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: linux_reservation.c,v 1.22 2021/12/19 01:50:18 riastradh Exp $");
+__KERNEL_RCSID(0, "$NetBSD: linux_reservation.c,v 1.23 2021/12/19 01:50:25 riastradh Exp $");
 
 #include <sys/param.h>
 #include <sys/poll.h>
@@ -256,7 +256,7 @@
        prealloc = robj->robj_prealloc;
 
        /* If there's an existing list, check it for space.  */
-       if (list != NULL) {
+       if (list) {
                /* If there's too many already, give up.  */
                if (list->shared_count == UINT32_MAX)
                        return -ENOMEM;
@@ -312,6 +312,9 @@
  *     reservation_object_write_commit to commit the writes.
  *
  *     Caller must have robj locked.
+ *
+ *     Implies membar_producer, i.e. store-before-store barrier.  Does
+ *     NOT serve as an acquire operation, however.
  */
 static void
 reservation_object_write_begin(struct reservation_object *robj,
@@ -330,6 +333,9 @@
  *     reservation_object_write_begin that returned ticket.
  *
  *     Caller must have robj locked.
+ *
+ *     Implies membar_producer, i.e. store-before-store barrier.  Does
+ *     NOT serve as a release operation, however.
  */
 static void
 reservation_object_write_commit(struct reservation_object *robj,
@@ -464,7 +470,7 @@
                KASSERT(list != NULL);
                KASSERT(list->shared_count < list->shared_max);
 
-               /* Begin an update.  */
+               /* Begin an update.  Implies membar_producer for fence.  */
                reservation_object_write_begin(robj, &ticket);
 
                /* Find a fence with the same context number.  */
@@ -512,7 +518,10 @@
                if (replace == NULL)
                        prealloc->shared[prealloc->shared_count++] = fence;
 
-               /* Now ready to replace the list.  Begin an update.  */
+               /*
+                * Now ready to replace the list.  Begin an update.
+                * Implies membar_producer for fence and prealloc.
+                */
                reservation_object_write_begin(robj, &ticket);
 
                /* Replace the list.  */
@@ -527,7 +536,7 @@
                 * (We are not in a position at this point to sleep
                 * waiting for activity on all CPUs.)
                 */
-               if (list != NULL)
+               if (list)
                        objlist_defer_free(list);
        }
 
@@ -572,7 +581,9 @@
        reservation_object_read_begin(robj, &ticket);
 
        /* If there is a shared list, grab it.  */
-       if ((list = robj->fence) != NULL) {
+       list = robj->fence;
+       __insn_barrier();
+       if (list) {
                /* Make sure the content of the list has been published.  */
                membar_datadep_consumer();
 
@@ -627,7 +638,9 @@
        }
 
        /* If there is an exclusive fence, grab it.  */
-       if ((fence = robj->fence_excl) != NULL) {
+       fence = robj->fence_excl;
+       __insn_barrier();
+       if (fence) {
                /* Make sure the content of the fence has been published.  */
                membar_datadep_consumer();
        }
@@ -707,7 +720,11 @@
        reservation_object_read_begin(robj, &ticket);
 
        /* If shared is requested and there is a shared list, test it.  */
-       if (shared && (list = robj->fence) != NULL) {
+       if (!shared)
+               goto excl;
+       list = robj->fence;
+       __insn_barrier();
+       if (list) {
                /* Make sure the content of the list has been published.  */
                membar_datadep_consumer();
 
@@ -738,8 +755,11 @@
                }
        }
 
+excl:
        /* If there is an exclusive fence, test it.  */
-       if ((fence = robj->fence_excl) != NULL) {
+       fence = robj->fence_excl;
+       __insn_barrier();
+       if (fence) {
                /* Make sure the content of the fence has been published.  */
                membar_datadep_consumer();
 
@@ -804,7 +824,11 @@
        reservation_object_read_begin(robj, &ticket);
 
        /* If shared is requested and there is a shared list, wait on it.  */
-       if (shared && (list = robj->fence) != NULL) {
+       if (!shared)
+               goto excl;
+       list = robj->fence;
+       __insn_barrier();
+       if (list) {
                /* Make sure the content of the list has been published.  */
                membar_datadep_consumer();
 
@@ -834,8 +858,11 @@
                }
        }
 
+excl:
        /* If there is an exclusive fence, test it.  */
-       if ((fence = robj->fence_excl) != NULL) {
+       fence = robj->fence_excl;
+       __insn_barrier();
+       if (fence) {
                /* Make sure the content of the fence has been published.  */
                membar_datadep_consumer();
 
@@ -976,7 +1003,11 @@
        reservation_object_read_begin(robj, &ticket);
 
        /* If we want to wait for all fences, get the shared list.  */
-       if ((events & POLLOUT) && (list = robj->fence) != NULL) do {
+       if (!(events & POLLOUT))
+               goto excl;
+       list = robj->fence;
+       __insn_barrier();
+       if (list) do {
                /* Make sure the content of the list has been published.  */
                membar_datadep_consumer();
 
@@ -1047,8 +1078,11 @@
                }
        } while (0);
 
+excl:
        /* We always wait for at least the exclusive fence, so get it.  */
-       if ((fence = robj->fence_excl) != NULL) do {
+       fence = robj->fence_excl;
+       __insn_barrier();
+       if (fence) do {
                /* Make sure the content of the fence has been published.  */
                membar_datadep_consumer();