To prevent lock ordering problems with the kernel lock, we need to make sure

we block all interrupts that can grab the kernel lock.  The simplest way to
achieve this is to make sure mutexes always raise the ipl to the highest
level that has interrupts that grab the kernel lock.  This will allow us
to have "mpsafe" interrupt handlers at lower priority levels.

No change for non-MULTIPROCESSOR kernels.

ok matthew@

1 files changed, 19 insertions, 2 deletions

diff --git a/sys/arch/i386/include/mutex.h b/sys/arch/i386/include/mutex.h
index de340320e57..b2fb16802bb 100644
--- a/sys/arch/i386/include/mutex.h
+++ b/sys/arch/i386/include/mutex.h
@@ -1,4 +1,4 @@
-/*	$OpenBSD: mutex.h,v 1.4 2011/03/23 16:54:35 pirofti Exp $	*/
+/*	$OpenBSD: mutex.h,v 1.5 2013/07/10 21:31:12 kettenis Exp $	*/
 
 /*
  * Copyright (c) 2004 Artur Grabowski <art@openbsd.org>
@@ -38,7 +38,24 @@ struct mutex {
 	void *mtx_owner;
 };
 
-#define MUTEX_INITIALIZER(IPL) { 0, (IPL), 0, NULL }
+/*
+ * To prevent lock ordering problems with the kernel lock, we need to
+ * make sure we block all interrupts that can grab the kernel lock.
+ * The simplest way to achieve this is to make sure mutexes always
+ * raise the interrupt priority level to the highest level that has
+ * interrupts that grab the kernel lock.
+ */
+#ifdef MULTIPROCESSOR
+#define __MUTEX_IPL(ipl) \
+    (((ipl) > IPL_NONE && (ipl) < IPL_VM) ? IPL_VM : (ipl))
+#else
+#define __MUTEX_IPL(ipl) (ipl)
+#endif
+
+#define MUTEX_INITIALIZER(ipl) { 0, __MUTEX_IPL((ipl)), 0, NULL }
+
+void __mtx_init(struct mutex *, int);
+#define mtx_init(mtx, ipl) __mtx_init((mtx), __MUTEX_IPL((ipl)))
 
 #define MUTEX_ASSERT_LOCKED(mtx) do {					\
 	if ((mtx)->mtx_lock != 1 ||					\