Index: sys/dev/acpica/acpi.c
===================================================================
--- sys/dev/acpica/acpi.c
+++ sys/dev/acpica/acpi.c
@@ -33,6 +33,7 @@
 #include "opt_acpi.h"
 
 #include <sys/param.h>
+#include <sys/buf.h>
 #include <sys/eventhandler.h>
 #include <sys/kernel.h>
 #include <sys/proc.h>
@@ -3070,6 +3071,11 @@
 
     EVENTHANDLER_INVOKE(power_suspend_early);
     stop_all_proc();
+    /*
+     * Sync all buffers to disk and give them a chance to drain before
+     * proceeding.
+     */
+    bufsyncwait(10, true);
     EVENTHANDLER_INVOKE(power_suspend);
 
 #ifdef EARLY_AP_STARTUP
Index: sys/kern/vfs_bio.c
===================================================================
--- sys/kern/vfs_bio.c
+++ sys/kern/vfs_bio.c
@@ -1323,12 +1323,11 @@
 }
 
 /*
- * Shutdown the system cleanly to prepare for reboot, halt, or power off.
+ * Sync the filesystems and wait a while for all buffers to be flushed.
  */
-void
-bufshutdown(int show_busybufs)
+bool
+bufsyncwait(int maxiter, bool first_buf_printf)
 {
-	static int first_buf_printf = 1;
 	struct buf *bp;
 	int iter, nbusy, pbusy;
 #ifndef PREEMPTION
@@ -1336,17 +1335,16 @@
 #endif
 
 	/*
-	 * Sync filesystems for shutdown
+	 * Sync filesystems for suspend / shutdown
 	 */
 	wdog_kern_pat(WD_LASTVAL);
 	kern_sync(curthread);
 
 	/*
-	 * With soft updates, some buffers that are
-	 * written will be remarked as dirty until other
-	 * buffers are written.
+	 * With soft updates, some buffers that are written will be
+	 * remarked as dirty until other buffers are written.
 	 */
-	for (iter = pbusy = 0; iter < 20; iter++) {
+	for (iter = pbusy = 0; iter < maxiter; iter++) {
 		nbusy = 0;
 		for (bp = &buf[nbuf]; --bp >= buf; )
 			if (isbufbusy(bp))
@@ -1358,7 +1356,7 @@
 		}
 		if (first_buf_printf) {
 			printf("Syncing disks, buffers remaining... ");
-			first_buf_printf = 0;
+			first_buf_printf = false;
 		}
 		printf("%d ", nbusy);
 		if (nbusy < pbusy)
@@ -1386,6 +1384,25 @@
 #endif
 	}
 	printf("\n");
+	return (first_buf_printf);
+}
+
+/*
+ * Shutdown the system cleanly to prepare for reboot, halt, or power off.
+ */
+void
+bufshutdown(int show_busybufs)
+{
+	static bool first_buf_printf = true;
+	struct buf *bp;
+	int nbusy;
+
+	/*
+	 * Try to clean all the buffers by repeatedly calling kern_sync() when dirty buffers
+	 * remain after the attempt.
+	 */
+	first_buf_printf = bufsyncwait(20, first_buf_printf);
+
 	/*
 	 * Count only busy local buffers to prevent forcing 
 	 * a fsck if we're just a client of a wedged NFS server
Index: sys/sys/buf.h
===================================================================
--- sys/sys/buf.h
+++ sys/sys/buf.h
@@ -520,6 +520,7 @@
 caddr_t	kern_vfs_bio_buffer_alloc(caddr_t v, long physmem_est);
 void	bufinit(void);
 void	bufshutdown(int);
+bool	bufsyncwait(int maxiter, bool first_buf_printf);
 void	bdata2bio(struct buf *bp, struct bio *bip);
 void	bwillwrite(void);
 int	buf_dirty_count_severe(void);