[src/trunk]: src/sys/arch/hppa/include hppa: Add missing barriers in cpu_swit...

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

details:   https://anonhg.NetBSD.org/src/rev/a1a88c9a1536
branches:  trunk
changeset: 373668:a1a88c9a1536
user:      riastradh <riastradh%NetBSD.org@localhost>
date:      Thu Feb 23 14:55:36 2023 +0000

description:
hppa: Add missing barriers in cpu_switchto.

PR kern/57240

Not sure hppa has ever had working MULTIPROCESSOR, so maybe no
pullups needed?

diffstat:

 sys/arch/hppa/include/cpu.h |  23 +++++++++++++++++++++--
 1 files changed, 21 insertions(+), 2 deletions(-)

diffs (37 lines):

diff -r 1ea5b2ca3002 -r a1a88c9a1536 sys/arch/hppa/include/cpu.h
--- a/sys/arch/hppa/include/cpu.h       Thu Feb 23 14:55:24 2023 +0000
+++ b/sys/arch/hppa/include/cpu.h       Thu Feb 23 14:55:36 2023 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: cpu.h,v 1.12 2021/11/02 11:26:04 ryo Exp $     */
+/*     $NetBSD: cpu.h,v 1.13 2023/02/23 14:55:36 riastradh Exp $       */
 
 /*     $OpenBSD: cpu.h,v 1.55 2008/07/23 17:39:35 kettenis Exp $       */
 
@@ -200,7 +200,26 @@
 #define        GET_CURLWP(r)           mfctl CR_CURCPU, r ! ldw CI_CURLWP(r), r
 #define        GET_CURLWP_SPACE(s, r)  mfctl CR_CURCPU, r ! ldw CI_CURLWP(s, r), r
 
-#define        SET_CURLWP(r,t)         mfctl CR_CURCPU, t ! stw r, CI_CURLWP(t)
+/*
+ * 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.
+ */
+#define        SET_CURLWP(r,t)         \
+       sync ! mfctl CR_CURCPU, t ! stw r, CI_CURLWP(t) ! sync
 
 #else /*  MULTIPROCESSOR */