Hold db_mtx when updating db_state

Commit 555ef90 did some general code refactoring for
dmu_buf_will_not_fill() and dmu_buf_will_fill(). However, the db_mtx was
not held when update db->db_state in those code block. The rest of the
dbuf code always holds the db_mtx when updating db_state. This is
important because cv_wait() db_changed is used to check for db_state
changes.

Updating dmu_buf_will_not_fill() and dmu_buf_will_fill() to hold the
db_mtx when updating db_state.

Reviewed-by: Alexander Motin <[email protected]>
Reviewed-by: Brian Behlendorf <[email protected]>
Signed-off-by: Brian Atkinson <[email protected]>
Closes #14875

Author: bwatkinson

module/zfs/dbuf.c

@@ -2716,8 +2716,10 @@ dmu_buf_will_not_fill(dmu_buf_t *db_fake, dmu_tx_t *tx)
 {
 	dmu_buf_impl_t *db = (dmu_buf_impl_t *)db_fake;
 
+	mutex_enter(&db->db_mtx);
 	db->db_state = DB_NOFILL;
 	DTRACE_SET_STATE(db, "allocating NOFILL buffer");
+	mutex_exit(&db->db_mtx);
 
 	dbuf_noread(db);
 	(void) dbuf_dirty(db, tx);
@@ -2736,18 +2738,18 @@ dmu_buf_will_fill(dmu_buf_t *db_fake, dmu_tx_t *tx)
 	ASSERT(db->db.db_object != DMU_META_DNODE_OBJECT ||
 	    dmu_tx_private_ok(tx));
 
+	mutex_enter(&db->db_mtx);
 	if (db->db_state == DB_NOFILL) {
 		/*
 		 * Block cloning: We will be completely overwriting a block
 		 * cloned in this transaction group, so let's undirty the
 		 * pending clone and mark the block as uncached. This will be
 		 * as if the clone was never done.
 		 */
-		mutex_enter(&db->db_mtx);
 		VERIFY(!dbuf_undirty(db, tx));
-		mutex_exit(&db->db_mtx);
 		db->db_state = DB_UNCACHED;
 	}
+	mutex_exit(&db->db_mtx);
 
 	dbuf_noread(db);
 	(void) dbuf_dirty(db, tx);