Module Name: src
Committed By: ad
Date: Fri Jan 24 20:05:15 UTC 2020
Modified Files:
src/sys/kern: kern_lock.c kern_synch.c
Log Message:
Carefully put kernel_lock back the way it was, and add a comment hinting
that changing it is not a good idea, and hopefully nobody will ever try to
change it ever again.
To generate a diff of this commit:
cvs rdiff -u -r1.166 -r1.167 src/sys/kern/kern_lock.c
cvs rdiff -u -r1.337 -r1.338 src/sys/kern/kern_synch.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_lock.c
diff -u src/sys/kern/kern_lock.c:1.166 src/sys/kern/kern_lock.c:1.167
--- src/sys/kern/kern_lock.c:1.166 Wed Jan 22 13:19:33 2020
+++ src/sys/kern/kern_lock.c Fri Jan 24 20:05:15 2020
@@ -1,4 +1,4 @@
-/* $NetBSD: kern_lock.c,v 1.166 2020/01/22 13:19:33 ad Exp $ */
+/* $NetBSD: kern_lock.c,v 1.167 2020/01/24 20:05:15 ad Exp $ */
/*-
* Copyright (c) 2002, 2006, 2007, 2008, 2009, 2020 The NetBSD Foundation, Inc.
@@ -31,7 +31,7 @@
*/
#include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: kern_lock.c,v 1.166 2020/01/22 13:19:33 ad Exp $");
+__KERNEL_RCSID(0, "$NetBSD: kern_lock.c,v 1.167 2020/01/24 20:05:15 ad Exp $");
#include <sys/param.h>
#include <sys/proc.h>
@@ -156,6 +156,11 @@ _kernel_lock_dump(const volatile void *j
/*
* Acquire 'nlocks' holds on the kernel lock.
+ *
+ * Although it may not look it, this is one of the most central, intricate
+ * routines in the kernel, and tons of code elsewhere depends on its exact
+ * behaviour. If you change something in here, expect it to bite you in the
+ * rear.
*/
void
_kernel_lock(int nlocks)
@@ -164,7 +169,6 @@ _kernel_lock(int nlocks)
LOCKSTAT_TIMER(spintime);
LOCKSTAT_FLAG(lsflag);
struct lwp *owant;
- u_int count;
#ifdef LOCKDEBUG
u_int spins = 0;
#endif
@@ -210,16 +214,15 @@ _kernel_lock(int nlocks)
*/
membar_producer();
owant = ci->ci_biglock_wanted;
+ ci->ci_biglock_wanted = l;
/*
- * Stay pinned to the CPU and spin until we acquire the lock. Once
- * we have it, record the time spent with lockstat.
+ * Spin until we acquire the lock. Once we have it, record the
+ * time spent with lockstat.
*/
- l->l_nopreempt++;
LOCKSTAT_ENTER(lsflag);
LOCKSTAT_START_TIMER(lsflag, spintime);
- count = SPINLOCK_BACKOFF_MIN;
do {
splx(s);
while (__SIMPLELOCK_LOCKED_P(kernel_lock)) {
@@ -230,24 +233,12 @@ _kernel_lock(int nlocks)
_KERNEL_LOCK_ABORT("spinout");
}
#endif
- SPINLOCK_BACKOFF(count);
- if (count == SPINLOCK_BACKOFF_MAX) {
- /* Ok, waiting for real. */
- ci->ci_biglock_wanted = l;
- }
}
s = splvm();
} while (!__cpu_simple_lock_try(kernel_lock));
- /*
- * Got it; not re-enable preemption, although we now can't do a
- * preemption as kernel_lock is held!
- */
- l->l_nopreempt--;
ci->ci_biglock_count = nlocks;
l->l_blcnt = nlocks;
- splx(s);
-
LOCKSTAT_STOP_TIMER(lsflag, spintime);
LOCKDEBUG_LOCKED(kernel_lock_dodebug, kernel_lock, NULL,
RETURN_ADDRESS, 0);
@@ -256,6 +247,7 @@ _kernel_lock(int nlocks)
LB_KERNEL_LOCK | LB_SPIN, 1, spintime, RETURN_ADDRESS);
}
LOCKSTAT_EXIT(lsflag);
+ splx(s);
/*
* Now that we have kernel_lock, reset ci_biglock_wanted. This
Index: src/sys/kern/kern_synch.c
diff -u src/sys/kern/kern_synch.c:1.337 src/sys/kern/kern_synch.c:1.338
--- src/sys/kern/kern_synch.c:1.337 Wed Jan 22 13:19:33 2020
+++ src/sys/kern/kern_synch.c Fri Jan 24 20:05:15 2020
@@ -1,4 +1,4 @@
-/* $NetBSD: kern_synch.c,v 1.337 2020/01/22 13:19:33 ad Exp $ */
+/* $NetBSD: kern_synch.c,v 1.338 2020/01/24 20:05:15 ad Exp $ */
/*-
* Copyright (c) 1999, 2000, 2004, 2006, 2007, 2008, 2009, 2019
@@ -69,7 +69,7 @@
*/
#include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: kern_synch.c,v 1.337 2020/01/22 13:19:33 ad Exp $");
+__KERNEL_RCSID(0, "$NetBSD: kern_synch.c,v 1.338 2020/01/24 20:05:15 ad Exp $");
#include "opt_kstack.h"
#include "opt_dtrace.h"
@@ -353,7 +353,8 @@ kpreempt(uintptr_t where)
break;
}
s = splsched();
- if (__predict_false(l->l_blcnt != 0)) {
+ if (__predict_false(l->l_blcnt != 0 ||
+ curcpu()->ci_biglock_wanted != NULL)) {
/* Hold or want kernel_lock, code is not MT safe. */
splx(s);
if ((dop & DOPREEMPT_COUNTED) == 0) {
