Module Name: src
Committed By: ozaki-r
Date: Fri Nov 17 09:26:36 UTC 2017
Modified Files:
src/sys/kern: subr_localcount.c
src/sys/sys: localcount.h
Log Message:
Implement a debugging facility (overflow/underflow detection) for localcount
We cannot get an accurate count from a localcount instance because it consists
of per-cpu counters and we have no way to sum them up atomically. So we cannot
detect counter overflow/underflow as we can do on a normal refcount.
The facility adds an atomic counter to each localcount instance to enable the
validations. The counter ups and downs in synchronization with the per-CPU
counters. The counter is used iff both DEBUG and LOCKDEBUG are enabled in the
kernel.
Discussed on tech-kern@
To generate a diff of this commit:
cvs rdiff -u -r1.6 -r1.7 src/sys/kern/subr_localcount.c
cvs rdiff -u -r1.4 -r1.5 src/sys/sys/localcount.h
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/subr_localcount.c
diff -u src/sys/kern/subr_localcount.c:1.6 src/sys/kern/subr_localcount.c:1.7
--- src/sys/kern/subr_localcount.c:1.6 Mon Jun 12 21:08:34 2017
+++ src/sys/kern/subr_localcount.c Fri Nov 17 09:26:36 2017
@@ -1,4 +1,4 @@
-/* $NetBSD: subr_localcount.c,v 1.6 2017/06/12 21:08:34 riastradh Exp $ */
+/* $NetBSD: subr_localcount.c,v 1.7 2017/11/17 09:26:36 ozaki-r Exp $ */
/*-
* Copyright (c) 2016 The NetBSD Foundation, Inc.
@@ -44,7 +44,7 @@
*/
#include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: subr_localcount.c,v 1.6 2017/06/12 21:08:34 riastradh Exp $");
+__KERNEL_RCSID(0, "$NetBSD: subr_localcount.c,v 1.7 2017/11/17 09:26:36 ozaki-r Exp $");
#include <sys/param.h>
#include <sys/localcount.h>
@@ -54,6 +54,9 @@ __KERNEL_RCSID(0, "$NetBSD: subr_localco
#include <sys/mutex.h>
#include <sys/percpu.h>
#include <sys/xcall.h>
+#if defined(DEBUG) && defined(LOCKDEBUG)
+#include <sys/atomic.h>
+#endif
static void localcount_xc(void *, void *);
@@ -209,6 +212,10 @@ localcount_acquire(struct localcount *lc
KASSERT(lc->lc_totalp == NULL);
localcount_adjust(lc, +1);
+#if defined(DEBUG) && defined(LOCKDEBUG)
+ if (atomic_inc_32_nv(&lc->lc_refcnt) == 0)
+ panic("counter overflow");
+#endif
}
/*
@@ -253,5 +260,26 @@ localcount_release(struct localcount *lc
}
localcount_adjust(lc, -1);
+#if defined(DEBUG) && defined(LOCKDEBUG)
+ if (atomic_dec_32_nv(&lc->lc_refcnt) == UINT_MAX)
+ panic("counter underflow");
+#endif
out: kpreempt_enable();
}
+
+/*
+ * localcount_debug_refcnt(lc)
+ *
+ * Return a total reference count of lc. It returns a correct value
+ * only if DEBUG and LOCKDEBUG enabled. Otherwise always return 0.
+ */
+uint32_t
+localcount_debug_refcnt(const struct localcount *lc)
+{
+
+#if defined(DEBUG) && defined(LOCKDEBUG)
+ return lc->lc_refcnt;
+#else
+ return 0;
+#endif
+}
Index: src/sys/sys/localcount.h
diff -u src/sys/sys/localcount.h:1.4 src/sys/sys/localcount.h:1.5
--- src/sys/sys/localcount.h:1.4 Fri Jun 2 00:32:12 2017
+++ src/sys/sys/localcount.h Fri Nov 17 09:26:36 2017
@@ -1,4 +1,4 @@
-/* $NetBSD: localcount.h,v 1.4 2017/06/02 00:32:12 chs Exp $ */
+/* $NetBSD: localcount.h,v 1.5 2017/11/17 09:26:36 ozaki-r Exp $ */
/*-
* Copyright (c) 2016 The NetBSD Foundation, Inc.
@@ -43,8 +43,9 @@ struct kmutex;
struct percpu;
struct localcount {
- int64_t *lc_totalp;
- struct percpu *lc_percpu; /* int64_t */
+ int64_t *lc_totalp;
+ struct percpu *lc_percpu; /* int64_t */
+ volatile uint32_t lc_refcnt; /* only for debugging */
};
void localcount_init(struct localcount *);
@@ -55,4 +56,7 @@ void localcount_acquire(struct localcoun
void localcount_release(struct localcount *, struct kcondvar *,
struct kmutex *);
+uint32_t
+ localcount_debug_refcnt(const struct localcount *);
+
#endif /* _SYS_LOCALCOUNT_H */
