Index: sys/kern/vfs_bio.c
===================================================================
--- sys/kern/vfs_bio.c
+++ sys/kern/vfs_bio.c
@@ -4524,7 +4524,10 @@
 	mtxp = mtx_pool_find(mtxpool_sleep, bp);
 	mtx_lock(mtxp);
 	bp->b_flags |= B_DONE;
-	wakeup(bp);
+	if (bp->b_flags & B_WAITING) {
+		bp->b_flags &= ~B_WAITING;
+		wakeup(bp);
+	}
 	mtx_unlock(mtxp);
 }
 
@@ -4535,8 +4538,10 @@
 
 	mtxp = mtx_pool_find(mtxpool_sleep, bp);
 	mtx_lock(mtxp);
-	while ((bp->b_flags & B_DONE) == 0)
+	while ((bp->b_flags & B_DONE) == 0) {
+		bp->b_flags |= B_WAITING;
 		msleep(bp, mtxp, pri, wchan, 0);
+	}
 	mtx_unlock(mtxp);
 }
 
Index: sys/sys/buf.h
===================================================================
--- sys/sys/buf.h
+++ sys/sys/buf.h
@@ -199,7 +199,7 @@
 #define	B_CACHE		0x00000020	/* Bread found us in the cache. */
 #define	B_VALIDSUSPWRT	0x00000040	/* Valid write during suspension. */
 #define	B_DELWRI	0x00000080	/* Delay I/O until buffer reused. */
-#define	B_00000100	0x00000100	/* Available flag. */
+#define	B_WAITING	0x00000100	/* Waiter(s) active in bwait(). */
 #define	B_DONE		0x00000200	/* I/O completed. */
 #define	B_EINTR		0x00000400	/* I/O was interrupted */
 #define	B_NOREUSE	0x00000800	/* Contents not reused once released. */