sql: use RLock in connExecutor.CancelQuery and connExecutor.CancelAct…

…iveQueries

Fixes #95994

`connExecutor.CancelQuery` and `connExecutor.CancelActiveQueries` do not
modify `mu.ActiveQueries` or the `*queryMetas` inside so they can safely
use `RLock` instead of `Lock`.

Release note: None

pkg/server/status.go

@@ -3056,7 +3056,7 @@ func (s *statusServer) CancelSession(
 		}, nil
 	}
 
-	if err := s.checkCancelPrivilege(ctx, reqUsername, session.BaseSessionUser()); err != nil {
+	if err := s.checkCancelPrivilege(ctx, reqUsername, session.SessionUser()); err != nil {
 		// NB: not using serverError() here since the priv checker
 		// already returns a proper gRPC error status.
 		return nil, err
@@ -3109,7 +3109,7 @@ func (s *statusServer) CancelQuery(
 		}, nil
 	}
 
-	if err := s.checkCancelPrivilege(ctx, reqUsername, session.BaseSessionUser()); err != nil {
+	if err := s.checkCancelPrivilege(ctx, reqUsername, session.SessionUser()); err != nil {
 		// NB: not using serverError() here since the priv checker
 		// already returns a proper gRPC error status.
 		return nil, err

pkg/sql/conn_executor.go

@@ -3144,22 +3144,26 @@ func (ex *connExecutor) hasQuery(queryID clusterunique.ID) bool {
 
 // CancelQuery is part of the RegistrySession interface.
 func (ex *connExecutor) CancelQuery(queryID clusterunique.ID) bool {
-	ex.mu.Lock()
-	defer ex.mu.Unlock()
+	// RLock can be used because map deletion happens in
+	// connExecutor.removeActiveQuery.
+	ex.mu.RLock()
+	defer ex.mu.RUnlock()
 	if queryMeta, exists := ex.mu.ActiveQueries[queryID]; exists {
-		queryMeta.cancel()
+		queryMeta.cancelQuery()
 		return true
 	}
 	return false
 }
 
 // CancelActiveQueries is part of the RegistrySession interface.
 func (ex *connExecutor) CancelActiveQueries() bool {
-	ex.mu.Lock()
-	defer ex.mu.Unlock()
+	// RLock can be used because map deletion happens in
+	// connExecutor.removeActiveQuery.
+	ex.mu.RLock()
+	defer ex.mu.RUnlock()
 	canceled := false
 	for _, queryMeta := range ex.mu.ActiveQueries {
-		queryMeta.cancel()
+		queryMeta.cancelQuery()
 		canceled = true
 	}
 	return canceled
@@ -3174,13 +3178,10 @@ func (ex *connExecutor) CancelSession() {
 	ex.onCancelSession()
 }
 
-// user is part of the RegistrySession interface.
-func (ex *connExecutor) user() username.SQLUsername {
-	return ex.sessionData().User()
-}
-
-// BaseSessionUser is part of the RegistrySession interface.
-func (ex *connExecutor) BaseSessionUser() username.SQLUsername {
+// SessionUser is part of the RegistrySession interface.
+func (ex *connExecutor) SessionUser() username.SQLUsername {
+	// SessionUser is the same for all elements in the stack so use Base()
+	// to avoid needing a lock and race conditions.
 	return ex.sessionDataStack.Base().SessionUser()
 }
 

pkg/sql/exec_util.go

@@ -2034,12 +2034,6 @@ type queryMeta struct {
 	database string
 }
 
-// cancel cancels the query associated with this queryMeta, by closing the
-// associated stmt context.
-func (q *queryMeta) cancel() {
-	q.cancelQuery()
-}
-
 // SessionDefaults mirrors fields in Session, for restoring default
 // configuration values in SET ... TO DEFAULT (or RESET ...) statements.
 type SessionDefaults map[string]string
@@ -2138,9 +2132,8 @@ func (r *SessionRegistry) deregister(
 }
 
 type RegistrySession interface {
-	user() username.SQLUsername
-	// BaseSessionUser returns the base session's username.
-	BaseSessionUser() username.SQLUsername
+	// SessionUser returns the session user's username.
+	SessionUser() username.SQLUsername
 	hasQuery(queryID clusterunique.ID) bool
 	// CancelQuery cancels the query specified by queryID if it exists.
 	CancelQuery(queryID clusterunique.ID) bool