Unify SIGHUP handling between normal and walsender backends.

Because walsender and normal backends share the same main loop it's
problematic to have two different flag variables, set in signal
handlers, indicating a pending configuration reload.  Only certain
walsender commands reach code paths checking for the
variable (START_[LOGICAL_]REPLICATION, CREATE_REPLICATION_SLOT
... LOGICAL, notably not base backups).

This is a bug present since the introduction of walsender, but has
gotten worse in releases since then which allow walsender to do more.

A later patch, not slated for v10, will similarly unify SIGHUP
handling in other types of processes as well.

Author: Petr Jelinek, Andres Freund
Reviewed-By: Michael Paquier
Discussion: https://postgr.es/m/20170423235941.qosiuoyqprq4nu7v@alap3.anarazel.de
Backpatch: 9.2-, bug is present since 9.0

src/backend/replication/walsender.c

@@ -182,7 +182,6 @@ static bool streamingDoneReceiving;
 static bool WalSndCaughtUp = false;
 
 /* Flags set by signal handlers for later service in main loop */
-static volatile sig_atomic_t got_SIGHUP = false;
 static volatile sig_atomic_t got_SIGUSR2 = false;
 static volatile sig_atomic_t got_STOPPING = false;
 
@@ -218,7 +217,6 @@ static struct
 }	LagTracker;
 
 /* Signal handlers */
-static void WalSndSigHupHandler(SIGNAL_ARGS);
 static void WalSndLastCycleHandler(SIGNAL_ARGS);
 
 /* Prototypes for private functions */
@@ -1201,9 +1199,9 @@ WalSndWriteData(LogicalDecodingContext *ctx, XLogRecPtr lsn, TransactionId xid,
 		CHECK_FOR_INTERRUPTS();
 
 		/* Process any requests or signals received recently */
-		if (got_SIGHUP)
+		if (ConfigReloadPending)
 		{
-			got_SIGHUP = false;
+			ConfigReloadPending = false;
 			ProcessConfigFile(PGC_SIGHUP);
 			SyncRepInitConfig();
 		}
@@ -1309,9 +1307,9 @@ WalSndWaitForWal(XLogRecPtr loc)
 		CHECK_FOR_INTERRUPTS();
 
 		/* Process any requests or signals received recently */
-		if (got_SIGHUP)
+		if (ConfigReloadPending)
 		{
-			got_SIGHUP = false;
+			ConfigReloadPending = false;
 			ProcessConfigFile(PGC_SIGHUP);
 			SyncRepInitConfig();
 		}
@@ -2101,9 +2099,9 @@ WalSndLoop(WalSndSendDataCallback send_data)
 		CHECK_FOR_INTERRUPTS();
 
 		/* Process any requests or signals received recently */
-		if (got_SIGHUP)
+		if (ConfigReloadPending)
 		{
-			got_SIGHUP = false;
+			ConfigReloadPending = false;
 			ProcessConfigFile(PGC_SIGHUP);
 			SyncRepInitConfig();
 		}
@@ -2908,19 +2906,6 @@ HandleWalSndInitStopping(void)
 		got_STOPPING = true;
 }
 
-/* SIGHUP: set flag to re-read config file at next convenient time */
-static void
-WalSndSigHupHandler(SIGNAL_ARGS)
-{
-	int			save_errno = errno;
-
-	got_SIGHUP = true;
-
-	SetLatch(MyLatch);
-
-	errno = save_errno;
-}
-
 /*
  * SIGUSR2: set flag to do a last cycle and shut down afterwards. The WAL
  * sender should already have been switched to WALSNDSTATE_STOPPING at
@@ -2942,7 +2927,7 @@ void
 WalSndSignals(void)
 {
 	/* Set up signal handlers */
-	pqsignal(SIGHUP, WalSndSigHupHandler);		/* set flag to read config
+	pqsignal(SIGHUP, PostgresSigHupHandler);	/* set flag to read config
 												 * file */
 	pqsignal(SIGINT, SIG_IGN);	/* not used */
 	pqsignal(SIGTERM, die);		/* request shutdown */

src/backend/tcop/postgres.c

@@ -122,13 +122,6 @@ char	   *stack_base_ptr = NULL;
 char	   *register_stack_base_ptr = NULL;
 #endif
 
-/*
- * Flag to mark SIGHUP. Whenever the main loop comes around it
- * will reread the configuration file. (Better than doing the
- * reading in the signal handler, ey?)
- */
-static volatile sig_atomic_t got_SIGHUP = false;
-
 /*
  * Flag to keep track of whether we have started a transaction.
  * For extended query protocol this has to be remembered across messages.
@@ -187,7 +180,6 @@ static bool IsTransactionExitStmt(Node *parsetree);
 static bool IsTransactionExitStmtList(List *pstmts);
 static bool IsTransactionStmtList(List *pstmts);
 static void drop_unnamed_stmt(void);
-static void SigHupHandler(SIGNAL_ARGS);
 static void log_disconnections(int code, Datum arg);
 
 
@@ -2684,13 +2676,19 @@ FloatExceptionHandler(SIGNAL_ARGS)
 					   "invalid operation, such as division by zero.")));
 }
 
-/* SIGHUP: set flag to re-read config file at next convenient time */
-static void
-SigHupHandler(SIGNAL_ARGS)
+/*
+ * SIGHUP: set flag to re-read config file at next convenient time.
+ *
+ * Sets the ConfigReloadPending flag, which should be checked at convenient
+ * places inside main loops. (Better than doing the reading in the signal
+ * handler, ey?)
+ */
+void
+PostgresSigHupHandler(SIGNAL_ARGS)
 {
 	int			save_errno = errno;
 
-	got_SIGHUP = true;
+	ConfigReloadPending = true;
 	SetLatch(MyLatch);
 
 	errno = save_errno;
@@ -3632,8 +3630,8 @@ PostgresMain(int argc, char *argv[],
 		WalSndSignals();
 	else
 	{
-		pqsignal(SIGHUP, SigHupHandler);		/* set flag to read config
-												 * file */
+		pqsignal(SIGHUP, PostgresSigHupHandler);		/* set flag to read config
+														 * file */
 		pqsignal(SIGINT, StatementCancelHandler);		/* cancel current query */
 		pqsignal(SIGTERM, die); /* cancel current query and exit */
 
@@ -4046,9 +4044,9 @@ PostgresMain(int argc, char *argv[],
 		 * (6) check for any other interesting events that happened while we
 		 * slept.
 		 */
-		if (got_SIGHUP)
+		if (ConfigReloadPending)
 		{
-			got_SIGHUP = false;
+			ConfigReloadPending = false;
 			ProcessConfigFile(PGC_SIGHUP);
 		}
 

src/backend/utils/init/globals.c

@@ -31,6 +31,7 @@ volatile bool QueryCancelPending = false;
 volatile bool ProcDiePending = false;
 volatile bool ClientConnectionLost = false;
 volatile bool IdleInTransactionSessionTimeoutPending = false;
+volatile sig_atomic_t ConfigReloadPending = false;
 volatile uint32 InterruptHoldoffCount = 0;
 volatile uint32 QueryCancelHoldoffCount = 0;
 volatile uint32 CritSectionCount = 0;

src/include/miscadmin.h

@@ -23,6 +23,8 @@
 #ifndef MISCADMIN_H
 #define MISCADMIN_H
 
+#include <signal.h>
+
 #include "pgtime.h"				/* for pg_time_t */
 
 
@@ -81,6 +83,7 @@ extern PGDLLIMPORT volatile bool InterruptPending;
 extern PGDLLIMPORT volatile bool QueryCancelPending;
 extern PGDLLIMPORT volatile bool ProcDiePending;
 extern PGDLLIMPORT volatile bool IdleInTransactionSessionTimeoutPending;
+extern PGDLLIMPORT volatile sig_atomic_t ConfigReloadPending;
 
 extern volatile bool ClientConnectionLost;
 
@@ -273,6 +276,8 @@ extern void restore_stack_base(pg_stack_base_t base);
 extern void check_stack_depth(void);
 extern bool stack_is_too_deep(void);
 
+extern void PostgresSigHupHandler(SIGNAL_ARGS);
+
 /* in tcop/utility.c */
 extern void PreventCommandIfReadOnly(const char *cmdname);
 extern void PreventCommandIfParallelMode(const char *cmdname);