Remove few pointer dereferences in dbuf_read()

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Richard Yao <richard.yao@alumni.stonybrook.edu>
Reviewed-by: Ryan Moeller <ryan@iXsystems.com>
Signed-off-by: Alexander Motin <mav@FreeBSD.org>
Closes #14199
openzfs/zfs#14199

Change-Id: I73642a34711d27a43d5dd18e6fe5342570039af2

usr/src/uts/common/fs/zfs/dbuf.c

@@ -1158,8 +1158,8 @@ dbuf_read_verify_dnode_crypt(dmu_buf_impl_t *db, uint32_t flags)
 
 	ASSERT(MUTEX_HELD(&db->db_mtx));
 
-	if (!os->os_encrypted || os->os_raw_receive ||
-	    (flags & DB_RF_NO_DECRYPT) != 0)
+	if ((flags & DB_RF_NO_DECRYPT) != 0 ||
+	   !os->os_encrypted || os->os_raw_receive)
 		return (0);
 
 	DB_DNODE_ENTER(db);
@@ -1380,8 +1380,6 @@ dbuf_read(dmu_buf_impl_t *db, zio_t *zio, uint32_t flags)
 
 	mutex_enter(&db->db_mtx);
 	if (db->db_state == DB_CACHED) {
-		spa_t *spa = dn->dn_objset->os_spa;
-
 		/*
 		 * Ensure that this block's dnode has been decrypted if
 		 * the caller has requested decrypted data.
@@ -1400,6 +1398,7 @@ dbuf_read(dmu_buf_impl_t *db, zio_t *zio, uint32_t flags)
 		    (arc_is_encrypted(db->db_buf) ||
 		    arc_is_unauthenticated(db->db_buf) ||
 		    arc_get_compression(db->db_buf) != ZIO_COMPRESS_OFF)) {
+			spa_t *spa = dn->dn_objset->os_spa;
 			zbookmark_phys_t zb;
 
 			SET_BOOKMARK(&zb, dmu_objset_id(db->db_objset),
@@ -1415,13 +1414,13 @@ dbuf_read(dmu_buf_impl_t *db, zio_t *zio, uint32_t flags)
 		}
 		DB_DNODE_EXIT(db);
 	} else if (db->db_state == DB_UNCACHED) {
-		spa_t *spa = dn->dn_objset->os_spa;
 		boolean_t need_wait = B_FALSE;
 
 		db_lock_type_t dblt = dmu_buf_lock_parent(db, RW_READER, FTAG);
 
 		if (zio == NULL &&
 		    db->db_blkptr != NULL && !BP_IS_HOLE(db->db_blkptr)) {
+			spa_t *spa = dn->dn_objset->os_spa;
 			zio = zio_root(spa, NULL, NULL, ZIO_FLAG_CANFAIL);
 			need_wait = B_TRUE;
 		}

usr/src/uts/common/fs/zfs/dnode.c

@@ -2252,19 +2252,11 @@ dnode_spill_freed(dnode_t *dn)
 uint64_t
 dnode_block_freed(dnode_t *dn, uint64_t blkid)
 {
-	void *dp = spa_get_dsl(dn->dn_objset->os_spa);
 	int i;
 
 	if (blkid == DMU_BONUS_BLKID)
 		return (FALSE);
 
-	/*
-	 * If we're in the process of opening the pool, dp will not be
-	 * set yet, but there shouldn't be anything dirty.
-	 */
-	if (dp == NULL)
-		return (FALSE);
-
 	if (dn->dn_free_txg)
 		return (TRUE);