[src/trunk]: src/sys/arch/powerpc/powerpc powerpc: Add missing barriers in cp...

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

details:   https://anonhg.NetBSD.org/src/rev/974a8025210a
branches:  trunk
changeset: 373671:974a8025210a
user:      riastradh <riastradh%NetBSD.org@localhost>
date:      Thu Feb 23 14:56:11 2023 +0000

description:
powerpc: Add missing barriers in cpu_switchto.

Details in comments.

PR kern/57240

XXX pullup-8
XXX pullup-9
XXX pullup-10

diffstat:

 sys/arch/powerpc/powerpc/locore_subr.S |  39 +++++++++++++++++++++++++++++++++-
 1 files changed, 38 insertions(+), 1 deletions(-)

diffs (70 lines):

diff -r d6bb1cb01278 -r 974a8025210a sys/arch/powerpc/powerpc/locore_subr.S
--- a/sys/arch/powerpc/powerpc/locore_subr.S    Thu Feb 23 14:56:00 2023 +0000
+++ b/sys/arch/powerpc/powerpc/locore_subr.S    Thu Feb 23 14:56:11 2023 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: locore_subr.S,v 1.66 2022/03/16 09:48:23 andvar Exp $  */
+/*     $NetBSD: locore_subr.S,v 1.67 2023/02/23 14:56:11 riastradh Exp $       */
 
 /*
  * Copyright (c) 2001 Wasabi Systems, Inc.
@@ -215,7 +215,32 @@
         */
 
        GET_CPUINFO(%r7)
+
+       /*
+        * 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.
+        */
+#ifdef MULTIPROCESSOR
+       sync    /* store-before-store XXX use eieio if available -- cheaper */
+#endif
        stptr   %r31,CI_CURLWP(%r7)
+#ifdef MULTIPROCESSOR
+       sync    /* store-before-load */
+#endif
        mr      %r13,%r31
 #ifdef PPC_BOOKE
        mtsprg2 %r31                    /* save curlwp in sprg2 */
@@ -389,7 +414,13 @@
         * to a kernel thread
         */
 
+#ifdef MULTIPROCESSOR
+       sync    /* XXX eieio */         /* for mutex_enter; see cpu_switchto */
+#endif
        stptr   %r3, CI_CURLWP(%r7)
+#ifdef MULTIPROCESSOR
+       sync                            /* for mutex_enter; see cpu_switchto */
+#endif
        mr      %r13, %r3
 #ifdef PPC_BOOKE
        mtsprg2 %r3
@@ -423,7 +454,13 @@
 #endif
 
        GET_CPUINFO(%r7)
+#ifdef MULTIPROCESSOR
+       sync    /* XXX eieio */         /* for mutex_enter; see cpu_switchto */
+#endif
        stptr   %r30, CI_CURLWP(%r7)
+#ifdef MULTIPROCESSOR
+       sync                            /* for mutex_enter; see cpu_switchto */
+#endif
        mr      %r13, %r30
 #ifdef PPC_BOOKE
        mtsprg2 %r30