diff --git a/kmod/src/block.c b/kmod/src/block.c
index eb2c3b2e..9a004407 100644
--- a/kmod/src/block.c
+++ b/kmod/src/block.c
@@ -63,6 +63,7 @@ enum {
 	BLOCK_BIT_UPTODATE = 0,	/* contents consistent with media */
 	BLOCK_BIT_NEW,		/* newly allocated, contents undefined */
 	BLOCK_BIT_DIRTY,	/* dirty, writer will write */
+	BLOCK_BIT_IO_BUSY,	/* bios are in flight */
 	BLOCK_BIT_ERROR,	/* saw IO error */
 	BLOCK_BIT_DELETED,	/* has been deleted from rbtree */
 	BLOCK_BIT_PAGE_ALLOC,	/* page (possibly high order) allocation */
@@ -354,6 +355,12 @@ static void block_remove(struct super_block *sb, struct block_private *bp)
 	}
 }
 
+static bool io_busy(struct block_private *bp)
+{
+	smp_rmb(); /* test after adding to wait queue */
+	return test_bit(BLOCK_BIT_IO_BUSY, &bp->bits);
+}
+
 /*
  * Called during shutdown with no other users.
  */
@@ -366,7 +373,7 @@ static void block_remove_all(struct super_block *sb)
 	for (node = rb_first(&binf->root); node; ) {
 		bp = container_of(node, struct block_private, node);
 		node = rb_next(node);
-		wait_event(binf->waitq, atomic_read(&bp->io_count) == 0);
+		wait_event(binf->waitq, !io_busy(bp));
 		block_remove(sb, bp);
 	}
 
@@ -395,17 +402,19 @@ static void block_end_io(struct super_block *sb, int rw,
 		set_bit(BLOCK_BIT_ERROR, &bp->bits);
 	}
 
-	/* update bits before waiters see io_count == 0 */
-	if (atomic_read(&bp->io_count) == 1) {
-		if (is_read && !test_bit(BLOCK_BIT_ERROR, &bp->bits))
-			set_bit(BLOCK_BIT_UPTODATE, &bp->bits);
-	}
+	if (!atomic_dec_and_test(&bp->io_count))
+		return;
 
-	/* make sure bits are visible to woken */
-	smp_mb__after_atomic();
+	if (is_read && !test_bit(BLOCK_BIT_ERROR, &bp->bits))
+		set_bit(BLOCK_BIT_UPTODATE, &bp->bits);
 
-	/* then wake */
-	if (atomic_dec_and_test(&bp->io_count))
+	clear_bit(BLOCK_BIT_IO_BUSY, &bp->bits);
+	block_put(sb, bp);
+
+	/* make sure set and cleared bits are visible to woken */
+	smp_mb();
+
+	if (waitqueue_active(&binf->waitq))
 		wake_up(&binf->waitq);
 }
 
@@ -414,11 +423,9 @@ static void block_bio_end_io(struct bio *bio, int err)
 	struct block_private *bp = bio->bi_private;
 	struct super_block *sb = bp->sb;
 
-
+	TRACE_BLOCK(end_io, bp);
 	block_end_io(sb, bio->bi_rw, bp, err);
 	bio_put(bio);
-	TRACE_BLOCK(end_io, bp);
-	block_put(sb, bp);
 }
 
 /*
@@ -441,6 +448,8 @@ static int block_submit_bio(struct super_block *sb, struct block_private *bp,
 
 	/* don't let racing end_io during submission think block is complete */
 	atomic_inc(&bp->io_count);
+	set_bit(BLOCK_BIT_IO_BUSY, &bp->bits);
+	atomic_inc(&bp->refcount);
 
 	blk_start_plug(&plug);
 
@@ -457,7 +466,6 @@ static int block_submit_bio(struct super_block *sb, struct block_private *bp,
 			bio->bi_end_io = block_bio_end_io;
 			bio->bi_private = bp;
 
-			atomic_inc(&bp->refcount);
 			atomic_inc(&bp->io_count);
 
 			TRACE_BLOCK(submit, bp);
@@ -732,7 +740,7 @@ int scoutfs_block_writer_write(struct super_block *sb,
 
 	list_for_each_entry(bp, &wri->dirty_list, dirty_entry) {
 		/* XXX should this be interruptible? */
-		wait_event(binf->waitq, atomic_read(&bp->io_count) == 0);
+		wait_event(binf->waitq, !io_busy(bp));
 		if (ret == 0 && test_bit(BLOCK_BIT_ERROR, &bp->bits)) {
 			clear_bit(BLOCK_BIT_ERROR, &bp->bits);
 			ret = -EIO;