Module Name: src
Committed By: riastradh
Date: Thu Oct 5 13:05:18 UTC 2023
Modified Files:
src/sys/kern: kern_lwp.c
Log Message:
lwp_pctr(9): Make this a little more robust.
No substantive change to machine code on aarch64. (Instructions and
registers got reordered a little but not in a way that matters.)
To generate a diff of this commit:
cvs rdiff -u -r1.263 -r1.264 src/sys/kern/kern_lwp.c
Please note that diffs are not public domain; they are subject to the
copyright notices on the relevant files.
Modified files:
Index: src/sys/kern/kern_lwp.c
diff -u src/sys/kern/kern_lwp.c:1.263 src/sys/kern/kern_lwp.c:1.264
--- src/sys/kern/kern_lwp.c:1.263 Wed Oct 4 22:17:09 2023
+++ src/sys/kern/kern_lwp.c Thu Oct 5 13:05:18 2023
@@ -1,4 +1,4 @@
-/* $NetBSD: kern_lwp.c,v 1.263 2023/10/04 22:17:09 ad Exp $ */
+/* $NetBSD: kern_lwp.c,v 1.264 2023/10/05 13:05:18 riastradh Exp $ */
/*-
* Copyright (c) 2001, 2006, 2007, 2008, 2009, 2019, 2020, 2023
@@ -217,7 +217,7 @@
*/
#include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: kern_lwp.c,v 1.263 2023/10/04 22:17:09 ad Exp $");
+__KERNEL_RCSID(0, "$NetBSD: kern_lwp.c,v 1.264 2023/10/05 13:05:18 riastradh Exp $");
#include "opt_ddb.h"
#include "opt_lockdebug.h"
@@ -2144,12 +2144,23 @@ lwp_ctl_exit(void)
* Return the current LWP's "preemption counter". Used to detect
* preemption across operations that can tolerate preemption without
* crashing, but which may generate incorrect results if preempted.
+ *
+ * We do arithmetic in unsigned long to avoid undefined behaviour in
+ * the event of arithmetic overflow on LP32, and issue __insn_barrier()
+ * on both sides so this can safely be used to detect changes to the
+ * preemption counter in loops around other memory accesses even in the
+ * event of whole-program optimization (e.g., gcc -flto).
*/
long
lwp_pctr(void)
{
+ unsigned long pctr;
- return curlwp->l_ru.ru_nvcsw + curlwp->l_ru.ru_nivcsw;
+ __insn_barrier();
+ pctr = curlwp->l_ru.ru_nvcsw;
+ pctr += curlwp->l_ru.ru_nivcsw;
+ __insn_barrier();
+ return pctr;
}
/*
