[src/trunk]: src/sys/uvm/pmap Convert pmap_pvt to atomic_load/store.

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

details:   https://anonhg.NetBSD.org/src/rev/3260489effd0
branches:  trunk
changeset: 1005478:3260489effd0
user:      riastradh <riastradh%NetBSD.org@localhost>
date:      Mon Dec 09 04:39:58 2019 +0000

description:
Convert pmap_pvt to atomic_load/store.

diffstat:

 sys/uvm/pmap/pmap_pvt.c |  28 ++++++++++++++++++++--------
 1 files changed, 20 insertions(+), 8 deletions(-)

diffs (64 lines):

diff -r bc5099b84e6e -r 3260489effd0 sys/uvm/pmap/pmap_pvt.c
--- a/sys/uvm/pmap/pmap_pvt.c   Mon Dec 09 02:30:30 2019 +0000
+++ b/sys/uvm/pmap/pmap_pvt.c   Mon Dec 09 04:39:58 2019 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: pmap_pvt.c,v 1.4 2019/12/07 17:56:08 jmcneill Exp $    */
+/*     $NetBSD: pmap_pvt.c,v 1.5 2019/12/09 04:39:58 riastradh Exp $   */
 
 /*-
  * Copyright (c) 2014 The NetBSD Foundation, Inc.
@@ -30,7 +30,7 @@
  */
 
 #include <sys/cdefs.h>
-__RCSID("$NetBSD: pmap_pvt.c,v 1.4 2019/12/07 17:56:08 jmcneill Exp $");
+__RCSID("$NetBSD: pmap_pvt.c,v 1.5 2019/12/09 04:39:58 riastradh Exp $");
 
 #include <sys/kmem.h>
 #include <sys/pserialize.h>
@@ -92,8 +92,7 @@
 
        mutex_enter(&pv_unmanaged.lock);
        pvt->pvt_next = pv_unmanaged.list;
-       membar_producer();
-       pv_unmanaged.list = pvt;
+       atomic_store_release(&pv_unmanaged.list, pvt);
        mutex_exit(&pv_unmanaged.lock);
 }
 
@@ -119,9 +118,21 @@
                        panic("pmap_pv_untrack: pv-tracking at 0x%"PRIxPADDR
                            ": 0x%"PRIxPSIZE" bytes, not 0x%"PRIxPSIZE" bytes",
                            pvt->pvt_start, pvt->pvt_size, size);
-               *pvtp = pvt->pvt_next;
+
+               /*
+                * Remove from list.  Readers can safely see the old
+                * and new states of the list.
+                */
+               atomic_store_relaxed(pvtp, pvt->pvt_next);
+
+               /* Wait for readers who can see the old state to finish.  */
                pserialize_perform(pv_unmanaged.psz);
-               pvt->pvt_next = NULL;
+
+               /*
+                * We now have exclusive access to pvt and can destroy
+                * it.  Poison it to catch bugs.
+                */
+               explicit_memset(&pvt->pvt_next, 0x1a, sizeof pvt->pvt_next);
                goto out;
        }
        panic("pmap_pv_untrack: pages not pv-tracked at 0x%"PRIxPADDR
@@ -143,8 +154,9 @@
        KASSERT(pa == trunc_page(pa));
 
        s = pserialize_read_enter();
-       for (pvt = pv_unmanaged.list; pvt != NULL; pvt = pvt->pvt_next) {
-               membar_datadep_consumer();
+       for (pvt = atomic_load_consume(&pv_unmanaged.list);
+            pvt != NULL;
+            pvt = pvt->pvt_next) {
                if ((pvt->pvt_start <= pa) &&
                    ((pa - pvt->pvt_start) < pvt->pvt_size))
                        break;