database/sql: ensure all driver interfaces are called under single lock

Russ pointed out in a previous CL golang.org/cl/65731 that not only
was the locking incomplete, previous changes did not correctly
lock driver calls in other sections. After inspecting
driverConn, driverStmt, driverResult, Tx, and Rows structs
where driver interfaces are stored, I discovered a few more places
that failed to lock driver calls. The largest of these
was the parameter type converter "driverArgs".

driverArgs was typically called right before another call to the
driver in a locked region, so I made the entire driverArgs expect
a locked driver mutex and combined the region. This should not
be a problem because the connection is pulled out of the connection
pool either way so there shouldn't be contention.

Fixes #21117

Change-Id: I88d46f74dca25fb11a30f0bf8e79785a73133d23
Reviewed-on: https://go-review.googlesource.com/71433
Run-TryBot: Daniel Theophanes <kardianos@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Russ Cox <rsc@golang.org>

src/database/sql/sql_test.go

@@ -3157,6 +3157,9 @@ func TestIssue6081(t *testing.T) {
 // In the test, a context is canceled while the query is in process so
 // the internal rollback will run concurrently with the explicitly called
 // Tx.Rollback.
+//
+// The addition of calling rows.Next also tests
+// Issue 21117.
 func TestIssue18429(t *testing.T) {
 	db := newTestDB(t, "people")
 	defer closeDB(t, db)
@@ -3189,6 +3192,9 @@ func TestIssue18429(t *testing.T) {
 			// reported.
 			rows, _ := tx.QueryContext(ctx, "WAIT|"+qwait+"|SELECT|people|name|")
 			if rows != nil {
+				// Call Next to test Issue 21117 and check for races.
+				for rows.Next() {
+				}
 				rows.Close()
 			}
 			// This call will race with the context cancel rollback to complete