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Date:      Mon, 7 Sep 2009 08:37:25 +0000 (UTC)
From:      Attilio Rao <attilio@FreeBSD.org>
To:        src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-stable@freebsd.org, svn-src-stable-7@freebsd.org
Subject:   svn commit: r196912 - in stable/7/sys: kern sys
Message-ID:  <200909070837.n878bP79008232@svn.freebsd.org>

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Author: attilio
Date: Mon Sep  7 08:37:25 2009
New Revision: 196912
URL: http://svn.freebsd.org/changeset/base/196912

Log:
  MFC r196334:
  Add the macro ASSERT_ATOMIC_LOAD_PTR(), enabled through INVARIANTS,
  which asserts for the correct alignment of datas which need to be read
  atomically without locks.
  Use that macro in locking primitives.

Modified:
  stable/7/sys/kern/kern_mutex.c
  stable/7/sys/kern/kern_rwlock.c
  stable/7/sys/kern/kern_sx.c
  stable/7/sys/sys/systm.h

Modified: stable/7/sys/kern/kern_mutex.c
==============================================================================
--- stable/7/sys/kern/kern_mutex.c	Mon Sep  7 06:37:44 2009	(r196911)
+++ stable/7/sys/kern/kern_mutex.c	Mon Sep  7 08:37:25 2009	(r196912)
@@ -724,6 +724,9 @@ mtx_init(struct mtx *m, const char *name
 
 	MPASS((opts & ~(MTX_SPIN | MTX_QUIET | MTX_RECURSE |
 		MTX_NOWITNESS | MTX_DUPOK | MTX_NOPROFILE)) == 0);
+	ASSERT_ATOMIC_LOAD_PTR(m->mtx_lock,
+	    ("%s: mtx_lock not aligned for %s:%p", __func__, name,
+	    &m->mtx_lock));
 
 #ifdef MUTEX_DEBUG
 	/* Diagnostic and error correction */

Modified: stable/7/sys/kern/kern_rwlock.c
==============================================================================
--- stable/7/sys/kern/kern_rwlock.c	Mon Sep  7 06:37:44 2009	(r196911)
+++ stable/7/sys/kern/kern_rwlock.c	Mon Sep  7 08:37:25 2009	(r196912)
@@ -137,6 +137,9 @@ rw_init_flags(struct rwlock *rw, const c
 
 	MPASS((opts & ~(RW_DUPOK | RW_NOPROFILE | RW_NOWITNESS | RW_QUIET |
 	    RW_RECURSE)) == 0);
+	ASSERT_ATOMIC_LOAD_PTR(rw->rw_lock,
+	    ("%s: rw_lock not aligned for %s:%p", __func__, name,
+	    &rw->rw_lock));
 
 	flags = LO_UPGRADABLE | LO_RECURSABLE;
 	if (opts & RW_DUPOK)

Modified: stable/7/sys/kern/kern_sx.c
==============================================================================
--- stable/7/sys/kern/kern_sx.c	Mon Sep  7 06:37:44 2009	(r196911)
+++ stable/7/sys/kern/kern_sx.c	Mon Sep  7 08:37:25 2009	(r196912)
@@ -166,6 +166,9 @@ sx_init_flags(struct sx *sx, const char 
 
 	MPASS((opts & ~(SX_QUIET | SX_RECURSE | SX_NOWITNESS | SX_DUPOK |
 	    SX_NOPROFILE | SX_ADAPTIVESPIN)) == 0);
+	ASSERT_ATOMIC_LOAD_PTR(sx->sx_lock,
+	    ("%s: sx_lock not aligned for %s:%p", __func__, description,
+	    &sx->sx_lock));
 
 	flags = LO_RECURSABLE | LO_SLEEPABLE | LO_UPGRADABLE;
 	if (opts & SX_DUPOK)

Modified: stable/7/sys/sys/systm.h
==============================================================================
--- stable/7/sys/sys/systm.h	Mon Sep  7 06:37:44 2009	(r196911)
+++ stable/7/sys/sys/systm.h	Mon Sep  7 08:37:25 2009	(r196912)
@@ -96,6 +96,17 @@ extern int maxusers;		/* system tune hin
 #endif
 
 /*
+ * Assert that a pointer can be loaded from memory atomically.
+ *
+ * This assertion enforces stronger alignment than necessary.  For example,
+ * on some architectures, atomicity for unaligned loads will depend on
+ * whether or not the load spans multiple cache lines.
+ */
+#define	ASSERT_ATOMIC_LOAD_PTR(var, msg)				\
+	KASSERT(sizeof(var) == sizeof(void *) &&			\
+	    ((uintptr_t)&(var) & (sizeof(void *) - 1)) == 0, msg)
+
+/*
  * XXX the hints declarations are even more misplaced than most declarations
  * in this file, since they are needed in one file (per arch) and only used
  * in two files.



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