Don't use static storage for SaveTransactionCharacteristics().

This is pretty queasy-making on general principles, and the more so
once you notice that CommitTransactionCommand() is actually stomping
on the values saved by _SPI_commit().  It's okay as long as the
active values didn't change during HoldPinnedPortals(); but that's
a larger assumption than I think we want to make, especially since
the fix is so simple.

Discussion: https://postgr.es/m/1533956.1645731245@sss.pgh.pa.us

src/backend/access/transam/xact.c

@@ -2983,24 +2983,20 @@ StartTransactionCommand(void)
  * GUC system resets the characteristics at transaction end, so for example
  * just skipping the reset in StartTransaction() won't work.)
  */
-static int	save_XactIsoLevel;
-static bool save_XactReadOnly;
-static bool save_XactDeferrable;
-
 void
-SaveTransactionCharacteristics(void)
+SaveTransactionCharacteristics(SavedTransactionCharacteristics *s)
 {
-	save_XactIsoLevel = XactIsoLevel;
-	save_XactReadOnly = XactReadOnly;
-	save_XactDeferrable = XactDeferrable;
+	s->save_XactIsoLevel = XactIsoLevel;
+	s->save_XactReadOnly = XactReadOnly;
+	s->save_XactDeferrable = XactDeferrable;
 }
 
 void
-RestoreTransactionCharacteristics(void)
+RestoreTransactionCharacteristics(const SavedTransactionCharacteristics *s)
 {
-	XactIsoLevel = save_XactIsoLevel;
-	XactReadOnly = save_XactReadOnly;
-	XactDeferrable = save_XactDeferrable;
+	XactIsoLevel = s->save_XactIsoLevel;
+	XactReadOnly = s->save_XactReadOnly;
+	XactDeferrable = s->save_XactDeferrable;
 }
 
 
@@ -3011,9 +3007,9 @@ void
 CommitTransactionCommand(void)
 {
 	TransactionState s = CurrentTransactionState;
+	SavedTransactionCharacteristics savetc;
 
-	if (s->chain)
-		SaveTransactionCharacteristics();
+	SaveTransactionCharacteristics(&savetc);
 
 	switch (s->blockState)
 	{
@@ -3071,7 +3067,7 @@ CommitTransactionCommand(void)
 				StartTransaction();
 				s->blockState = TBLOCK_INPROGRESS;
 				s->chain = false;
-				RestoreTransactionCharacteristics();
+				RestoreTransactionCharacteristics(&savetc);
 			}
 			break;
 
@@ -3097,7 +3093,7 @@ CommitTransactionCommand(void)
 				StartTransaction();
 				s->blockState = TBLOCK_INPROGRESS;
 				s->chain = false;
-				RestoreTransactionCharacteristics();
+				RestoreTransactionCharacteristics(&savetc);
 			}
 			break;
 
@@ -3115,7 +3111,7 @@ CommitTransactionCommand(void)
 				StartTransaction();
 				s->blockState = TBLOCK_INPROGRESS;
 				s->chain = false;
-				RestoreTransactionCharacteristics();
+				RestoreTransactionCharacteristics(&savetc);
 			}
 			break;
 
@@ -3182,7 +3178,7 @@ CommitTransactionCommand(void)
 					StartTransaction();
 					s->blockState = TBLOCK_INPROGRESS;
 					s->chain = false;
-					RestoreTransactionCharacteristics();
+					RestoreTransactionCharacteristics(&savetc);
 				}
 			}
 			else if (s->blockState == TBLOCK_PREPARE)

src/backend/executor/spi.c

@@ -228,6 +228,7 @@ static void
 _SPI_commit(bool chain)
 {
 	MemoryContext oldcontext = CurrentMemoryContext;
+	SavedTransactionCharacteristics savetc;
 
 	/*
 	 * Complain if we are in a context that doesn't permit transaction
@@ -255,9 +256,8 @@ _SPI_commit(bool chain)
 				(errcode(ERRCODE_INVALID_TRANSACTION_TERMINATION),
 				 errmsg("cannot commit while a subtransaction is active")));
 
-	/* XXX this ain't re-entrant enough for my taste */
 	if (chain)
-		SaveTransactionCharacteristics();
+		SaveTransactionCharacteristics(&savetc);
 
 	/* Catch any error occurring during the COMMIT */
 	PG_TRY();
@@ -281,7 +281,7 @@ _SPI_commit(bool chain)
 		/* Immediately start a new transaction */
 		StartTransactionCommand();
 		if (chain)
-			RestoreTransactionCharacteristics();
+			RestoreTransactionCharacteristics(&savetc);
 
 		MemoryContextSwitchTo(oldcontext);
 
@@ -305,7 +305,7 @@ _SPI_commit(bool chain)
 		/* ... and start a new one */
 		StartTransactionCommand();
 		if (chain)
-			RestoreTransactionCharacteristics();
+			RestoreTransactionCharacteristics(&savetc);
 
 		MemoryContextSwitchTo(oldcontext);
 
@@ -333,6 +333,7 @@ static void
 _SPI_rollback(bool chain)
 {
 	MemoryContext oldcontext = CurrentMemoryContext;
+	SavedTransactionCharacteristics savetc;
 
 	/* see under SPI_commit() */
 	if (_SPI_current->atomic)
@@ -346,9 +347,8 @@ _SPI_rollback(bool chain)
 				(errcode(ERRCODE_INVALID_TRANSACTION_TERMINATION),
 				 errmsg("cannot roll back while a subtransaction is active")));
 
-	/* XXX this ain't re-entrant enough for my taste */
 	if (chain)
-		SaveTransactionCharacteristics();
+		SaveTransactionCharacteristics(&savetc);
 
 	/* Catch any error occurring during the ROLLBACK */
 	PG_TRY();
@@ -373,7 +373,7 @@ _SPI_rollback(bool chain)
 		/* Immediately start a new transaction */
 		StartTransactionCommand();
 		if (chain)
-			RestoreTransactionCharacteristics();
+			RestoreTransactionCharacteristics(&savetc);
 
 		MemoryContextSwitchTo(oldcontext);
 
@@ -398,7 +398,7 @@ _SPI_rollback(bool chain)
 		/* ... and start a new one */
 		StartTransactionCommand();
 		if (chain)
-			RestoreTransactionCharacteristics();
+			RestoreTransactionCharacteristics(&savetc);
 
 		MemoryContextSwitchTo(oldcontext);
 

src/include/access/xact.h

@@ -135,6 +135,14 @@ typedef enum
 typedef void (*SubXactCallback) (SubXactEvent event, SubTransactionId mySubid,
 								 SubTransactionId parentSubid, void *arg);
 
+/* Data structure for Save/RestoreTransactionCharacteristics */
+typedef struct SavedTransactionCharacteristics
+{
+	int			save_XactIsoLevel;
+	bool		save_XactReadOnly;
+	bool		save_XactDeferrable;
+} SavedTransactionCharacteristics;
+
 
 /* ----------------
  *		transaction-related XLOG entries
@@ -399,8 +407,8 @@ extern bool TransactionIdIsCurrentTransactionId(TransactionId xid);
 extern void CommandCounterIncrement(void);
 extern void ForceSyncCommit(void);
 extern void StartTransactionCommand(void);
-extern void SaveTransactionCharacteristics(void);
-extern void RestoreTransactionCharacteristics(void);
+extern void SaveTransactionCharacteristics(SavedTransactionCharacteristics *s);
+extern void RestoreTransactionCharacteristics(const SavedTransactionCharacteristics *s);
 extern void CommitTransactionCommand(void);
 extern void AbortCurrentTransaction(void);
 extern void BeginTransactionBlock(void);