[src/trunk]: src/sys/arch/ia64/ia64 ia64: Add missing barriers in cpu_switchto.

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

details:   https://anonhg.NetBSD.org/src/rev/63d6990cfb79
branches:  trunk
changeset: 373669:63d6990cfb79
user:      riastradh <riastradh%NetBSD.org@localhost>
date:      Thu Feb 23 14:55:47 2023 +0000

description:
ia64: Add missing barriers in cpu_switchto.

(ia64 has never really worked, so no pullups needed, right?)

PR kern/57240

diffstat:

 sys/arch/ia64/ia64/machdep.c    |   6 +++++-
 sys/arch/ia64/ia64/vm_machdep.c |  27 ++++++++++++++++++++++++---
 2 files changed, 29 insertions(+), 4 deletions(-)

diffs (69 lines):

diff -r a1a88c9a1536 -r 63d6990cfb79 sys/arch/ia64/ia64/machdep.c
--- a/sys/arch/ia64/ia64/machdep.c      Thu Feb 23 14:55:36 2023 +0000
+++ b/sys/arch/ia64/ia64/machdep.c      Thu Feb 23 14:55:47 2023 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: machdep.c,v 1.43 2019/04/19 16:28:32 scole Exp $       */
+/*     $NetBSD: machdep.c,v 1.44 2023/02/23 14:55:47 riastradh Exp $   */
 
 /*-
  * Copyright (c) 2003,2004 Marcel Moolenaar
@@ -638,6 +638,10 @@
 
        /*
         * Initialise process context. XXX: This should really be in cpu_switchto
+        *
+        * No membar needed because we're not switching from a
+        * previous lwp, and the idle lwp we're switching to can't be
+        * holding locks already; see cpu_switchto.
         */
        ci->ci_curlwp = &lwp0;
 
diff -r a1a88c9a1536 -r 63d6990cfb79 sys/arch/ia64/ia64/vm_machdep.c
--- a/sys/arch/ia64/ia64/vm_machdep.c   Thu Feb 23 14:55:36 2023 +0000
+++ b/sys/arch/ia64/ia64/vm_machdep.c   Thu Feb 23 14:55:47 2023 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: vm_machdep.c,v 1.17 2022/01/01 21:07:14 andvar Exp $   */
+/*     $NetBSD: vm_machdep.c,v 1.18 2023/02/23 14:55:47 riastradh Exp $        */
 
 /*
  * Copyright (c) 2006 The NetBSD Foundation, Inc.
@@ -37,6 +37,7 @@
 #include <sys/proc.h>
 #include <sys/systm.h>
 #include <sys/cpu.h>
+#include <sys/atomic.h>
 
 #include <machine/frame.h>
 #include <machine/md_var.h>
@@ -77,9 +78,29 @@
        register uint64_t reg9 __asm("r9");
 
        KASSERT(newlwp != NULL);
-       
+
+       /*
+        * Issue barriers to coordinate mutex_exit on this CPU with
+        * mutex_vector_enter on another CPU.
+        *
+        * 1. Any prior mutex_exit by oldlwp must be visible to other
+        *    CPUs before we set ci_curlwp := newlwp on this one,
+        *    requiring a store-before-store barrier.
+        *
+        * 2. ci_curlwp := newlwp must be visible on all other CPUs
+        *    before any subsequent mutex_exit by newlwp can even test
+        *    whether there might be waiters, requiring a
+        *    store-before-load barrier.
+        *
+        * See kern_mutex.c for details -- this is necessary for
+        * adaptive mutexes to detect whether the lwp is on the CPU in
+        * order to safely block without requiring atomic r/m/w in
+        * mutex_exit.
+        */
+       membar_producer();      /* store-before-store */
        ci->ci_curlwp = newlwp;
-       
+       membar_sync();          /* store-before-load */
+
        /* required for lwp_startup, copy oldlwp into r9, "mov r9=in0" */
        __asm __volatile("mov %0=%1" : "=r"(reg9) : "r"(oldlwp));