diff --git a/dm-sflc/src/lite/flush.c b/dm-sflc/src/lite/flush.c
index cac0922..25a1112 100644
--- a/dm-sflc/src/lite/flush.c
+++ b/dm-sflc/src/lite/flush.c
@@ -247,6 +247,7 @@ static int mark_posmap_blocks_clean(struct sflite_volume *svol)
  */
 int sflite_flush_posmap(struct sflite_volume *svol, struct bio *orig_bio, gfp_t gfp)
 {
+	unsigned nblocks = svol->sdev->posmap_size_blocks;
 	int err;
 
 	/* To prepare the CWBs (encrypt all the `dirty` blocks from `entries`
@@ -261,7 +262,7 @@ int sflite_flush_posmap(struct sflite_volume *svol, struct bio *orig_bio, gfp_t
 	if (err) {
 		// Clean up flush_pending: give up the FLUSH operation altogether
 		DMWARN("FLUSH: could not prepare_cwbs(): error %d", err);
-		bitmap_clear(svol->posmap.flush_pending, 0, svol->sdev->posmap_size_blocks);
+		bitmap_clear(svol->posmap.flush_pending, 0, nblocks);
 	}
 	up_write(&svol->posmap.flush_lock);
 	if (err)
@@ -282,10 +283,10 @@ int sflite_flush_posmap(struct sflite_volume *svol, struct bio *orig_bio, gfp_t
 		// Clean up and abort FLUSH operation.
 		DMWARN("FLUSH: could not send_cwbs(): error %d", err);
 		// All CWB callbacks have finished now, no locking needed
-		bitmap_clear(svol->posmap.cwb_error, 0, svol->sdev->posmap_size_blocks);
+		bitmap_clear(svol->posmap.cwb_error, 0, nblocks);
 		// Need to clear this one under rwsem
 		down_write(&svol->posmap.flush_lock);	// Not killable, for simplicity
-		bitmap_clear(svol->posmap.flush_pending, 0, svol->sdev->posmap_size_blocks);
+		bitmap_clear(svol->posmap.flush_pending, 0, nblocks);
 		up_write(&svol->posmap.flush_lock);
 		goto out;
 	}
@@ -299,10 +300,10 @@ int sflite_flush_posmap(struct sflite_volume *svol, struct bio *orig_bio, gfp_t
 		// Bummer, we got so far then the FLUSH failed. Clean up and abort.
 		DMWARN("FLUSH: could not issue_lowlevel_flush(): error %d", err);
 		// All CWB callbacks have finished now, no locking needed
-		bitmap_clear(svol->posmap.cwb_error, 0, svol->sdev->posmap_size_blocks);
+		bitmap_clear(svol->posmap.cwb_error, 0, nblocks);
 		// Need to clear this one under rwsem
 		down_write(&svol->posmap.flush_lock);	// Not killable, for simplicity
-		bitmap_clear(svol->posmap.flush_pending, 0, svol->sdev->posmap_size_blocks);
+		bitmap_clear(svol->posmap.flush_pending, 0, nblocks);
 		up_write(&svol->posmap.flush_lock);
 		goto out;
 	}
@@ -312,7 +313,13 @@ int sflite_flush_posmap(struct sflite_volume *svol, struct bio *orig_bio, gfp_t
 	 * did not change while we were not holding the locks.
 	 * If some CWBs failed, we return an error (then failing the upper-layer
 	 * bio in the caller, if there is one), but that doesn't mean aborting
-	 * entirely, because we can still mark some blocks as clean. */
+	 * entirely, because we can still mark some blocks as clean.
+	 * Here, we need to lock. */
+	down_write(&svol->posmap.flush_lock);	// Not killable, for simplicity
+	err = mark_posmap_blocks_clean(svol);
+	bitmap_clear(svol->posmap.cwb_error, 0, nblocks);
+	bitmap_clear(svol->posmap.flush_pending, 0, nblocks);
+	up_write(&svol->posmap.flush_lock);
 
 out:
 	if (orig_bio) {
@@ -327,28 +334,16 @@ out:
 void sflite_flush_work_fn(struct work_struct *work)
 {
 	struct sflite_io *io = container_of(work, struct sflite_io, work);
-	struct sflite_volume *svol = io->svol;
-	struct bio *orig_bio = io->orig_bio;
-	blk_status_t bi_status = BLK_STS_OK;
 	int err;
 
-	// Mutual exclusion with WRITEs, not with READs
-	if (down_write_killable(&svol->posmap.flush_lock)) {
-		bi_status = BLK_STS_IOERR;
-		goto endio;
-	}
-	// Just flush the position map: this function sleeps.
-	err = sflite_flush_posmap(svol, GFP_NOIO);
-	if (err) {
-		DMERR("Could not flush position map; error %d", err);
-		bi_status = BLK_STS_IOERR;
-	}
-	up_write(&svol->posmap.flush_lock);
-
-endio:
-	// Signal FLUSH completion
-	orig_bio->bi_status = bi_status;
-	bio_endio(orig_bio);
+	/* Everything is implemented in flush_posmap().
+	 * As for non-reentrancy: the block layer guarantees that at most one
+	 * FLUSH request is in-flight at any given time. The only other caller
+	 * of flush_posmap is the volume dtr(), which cannot be invoked if the
+	 * target is busy (e.g. I/O in flight) TODO double check */
+	err = sflite_flush_posmap(io->svol, io->orig_bio, GFP_NOIO);
+	io->orig_bio->bi_status = errno_to_blk_status(err);
+	bio_endio(io->orig_bio);
 
 	return;