dbuf: Handle arcbuf assignment after block cloning

In some cases dbuf_assign_arcbuf() may be called on a block that
was recently cloned.  If it happened in current TXG we must undo
the block cloning first, since the only one dirty record per TXG
can't and shouldn't mean both cloning and overwrite same time.

Reviewed-by: Kay Pedersen <[email protected]>
Reviewed-by: Brian Behlendorf <[email protected]>
Signed-off-by:	Alexander Motin <[email protected]>
Sponsored by:	iXsystems, Inc.
Closes #15653 

1 files changed, 11 insertions, 1 deletions

diff --git a/module/zfs/dbuf.c b/module/zfs/dbuf.c
index 5a7fe42b6..7691cd85f 100644
--- a/module/zfs/dbuf.c
+++ b/module/zfs/dbuf.c
@@ -2930,7 +2930,8 @@ dbuf_assign_arcbuf(dmu_buf_impl_t *db, arc_buf_t *buf, dmu_tx_t *tx)
 	while (db->db_state == DB_READ || db->db_state == DB_FILL)
 		cv_wait(&db->db_changed, &db->db_mtx);
 
-	ASSERT(db->db_state == DB_CACHED || db->db_state == DB_UNCACHED);
+	ASSERT(db->db_state == DB_CACHED || db->db_state == DB_UNCACHED ||
+	    db->db_state == DB_NOFILL);
 
 	if (db->db_state == DB_CACHED &&
 	    zfs_refcount_count(&db->db_holds) - 1 > db->db_dirtycnt) {
@@ -2967,6 +2968,15 @@ dbuf_assign_arcbuf(dmu_buf_impl_t *db, arc_buf_t *buf, dmu_tx_t *tx)
 			arc_buf_destroy(db->db_buf, db);
 		}
 		db->db_buf = NULL;
+	} else if (db->db_state == DB_NOFILL) {
+		/*
+		 * We will be completely replacing the cloned block.  In case
+		 * it was cloned in this transaction group, let's undirty the
+		 * pending clone and mark the block as uncached. This will be
+		 * as if the clone was never done.
+		 */
+		VERIFY(!dbuf_undirty(db, tx));
+		db->db_state = DB_UNCACHED;
 	}
 	ASSERT(db->db_buf == NULL);
 	dbuf_set_data(db, buf);