v10-0001-Give-the-postmaster-a-WaitEventSet-and-a-latch.patch

From 01bd9b3ef6029d5e5d568b514874a23a167d826d Mon Sep 17 00:00:00 2001
From: Thomas Munro <thomas.munro@gmail.com>
Date: Wed, 9 Nov 2022 22:59:58 +1300
Subject: [PATCH v10 1/2] Give the postmaster a WaitEventSet and a latch.

Switch to an architecture similar to regular backends, where signal
handlers just set flags instead of doing real work.

Changes:

 * Allow the postmaster to set up its own local latch.  For now, we don't
   want other backends setting a shared memory latch directly (but that
   could be made to work with more research on robustness).

 * The existing signal handlers are cut in two: a handle_pm_XXX part that
   sets a pending_pm_XXX variable and sets the local latch, and a
   process_pm_XXX part.

 * Signal handlers are now installed with the regular pqsignal()
   function rather then the special pqsignal_pm() function; the concerns
   about the portability of SA_RESTART vs select() are no longer
   relevant, as we are not using select() or relying on EINTR.

Reviewed-by: Andres Freund <andres@anarazel.de>
Discussion: https://postgr.es/m/CA%2BhUKG%2BZ-HpOj1JsO9eWUP%2Bar7npSVinsC_npxSy%2BjdOMsx%3DGg%40mail.gmail.com
---
 src/backend/libpq/pqcomm.c            |   3 +-
 src/backend/libpq/pqsignal.c          |  40 ---
 src/backend/postmaster/fork_process.c |  18 +-
 src/backend/postmaster/postmaster.c   | 412 +++++++++++++++-----------
 src/backend/tcop/postgres.c           |   1 -
 src/backend/utils/init/miscinit.c     |  13 +-
 src/include/libpq/pqsignal.h          |   3 -
 src/include/miscadmin.h               |   1 +
 8 files changed, 264 insertions(+), 227 deletions(-)

diff --git a/src/backend/libpq/pqcomm.c b/src/backend/libpq/pqcomm.c
index 7a043bf6b0..864c9debe8 100644
--- a/src/backend/libpq/pqcomm.c
+++ b/src/backend/libpq/pqcomm.c
@@ -683,8 +683,7 @@ Setup_AF_UNIX(const char *sock_path)
  *		server port.  Set port->sock to the FD of the new connection.
  *
  * ASSUME: that this doesn't need to be non-blocking because
- *		the Postmaster uses select() to tell when the socket is ready for
- *		accept().
+ *		the Postmaster waits for the socket to be ready to accept().
  *
  * RETURNS: STATUS_OK or STATUS_ERROR
  */
diff --git a/src/backend/libpq/pqsignal.c b/src/backend/libpq/pqsignal.c
index b815be6eea..d233e3a2fd 100644
--- a/src/backend/libpq/pqsignal.c
+++ b/src/backend/libpq/pqsignal.c
@@ -97,43 +97,3 @@ pqinitmask(void)
 	sigdelset(&StartupBlockSig, SIGALRM);
 #endif
 }
-
-/*
- * Set up a postmaster signal handler for signal "signo"
- *
- * Returns the previous handler.
- *
- * This is used only in the postmaster, which has its own odd approach to
- * signal handling.  For signals with handlers, we block all signals for the
- * duration of signal handler execution.  We also do not set the SA_RESTART
- * flag; this should be safe given the tiny range of code in which the
- * postmaster ever unblocks signals.
- *
- * pqinitmask() must have been invoked previously.
- */
-pqsigfunc
-pqsignal_pm(int signo, pqsigfunc func)
-{
-	struct sigaction act,
-				oact;
-
-	act.sa_handler = func;
-	if (func == SIG_IGN || func == SIG_DFL)
-	{
-		/* in these cases, act the same as pqsignal() */
-		sigemptyset(&act.sa_mask);
-		act.sa_flags = SA_RESTART;
-	}
-	else
-	{
-		act.sa_mask = BlockSig;
-		act.sa_flags = 0;
-	}
-#ifdef SA_NOCLDSTOP
-	if (signo == SIGCHLD)
-		act.sa_flags |= SA_NOCLDSTOP;
-#endif
-	if (sigaction(signo, &act, &oact) < 0)
-		return SIG_ERR;
-	return oact.sa_handler;
-}
diff --git a/src/backend/postmaster/fork_process.c b/src/backend/postmaster/fork_process.c
index 569b52e849..509587636e 100644
--- a/src/backend/postmaster/fork_process.c
+++ b/src/backend/postmaster/fork_process.c
@@ -12,24 +12,28 @@
 #include "postgres.h"
 
 #include <fcntl.h>
+#include <signal.h>
 #include <time.h>
 #include <sys/stat.h>
 #include <sys/time.h>
 #include <unistd.h>
 
+#include "libpq/pqsignal.h"
 #include "postmaster/fork_process.h"
 
 #ifndef WIN32
 /*
  * Wrapper for fork(). Return values are the same as those for fork():
  * -1 if the fork failed, 0 in the child process, and the PID of the
- * child in the parent process.
+ * child in the parent process.  Signals are blocked while forking, so
+ * the child must unblock.
  */
 pid_t
 fork_process(void)
 {
 	pid_t		result;
 	const char *oomfilename;
+	sigset_t	save_mask;
 
 #ifdef LINUX_PROFILE
 	struct itimerval prof_itimer;
@@ -51,6 +55,13 @@ fork_process(void)
 	getitimer(ITIMER_PROF, &prof_itimer);
 #endif
 
+	/*
+	 * We start postmaster children with signals blocked.  This allows them to
+	 * install their own handlers before unblocking, to avoid races where they
+	 * might run the postmaster's handler and miss an important control signal.
+	 * With more analysis this could potentially be relaxed.
+	 */
+	sigprocmask(SIG_SETMASK, &BlockSig, &save_mask);
 	result = fork();
 	if (result == 0)
 	{
@@ -103,6 +114,11 @@ fork_process(void)
 		/* do post-fork initialization for random number generation */
 		pg_strong_random_init();
 	}
+	else
+	{
+		/* in parent, restore signal mask */
+		sigprocmask(SIG_SETMASK, &save_mask, NULL);
+	}
 
 	return result;
 }
diff --git a/src/backend/postmaster/postmaster.c b/src/backend/postmaster/postmaster.c
index eac3450774..8bbc1042a5 100644
--- a/src/backend/postmaster/postmaster.c
+++ b/src/backend/postmaster/postmaster.c
@@ -70,7 +70,6 @@
 #include <time.h>
 #include <sys/wait.h>
 #include <ctype.h>
-#include <sys/select.h>
 #include <sys/stat.h>
 #include <sys/socket.h>
 #include <fcntl.h>
@@ -362,6 +361,17 @@ static volatile sig_atomic_t WalReceiverRequested = false;
 static volatile bool StartWorkerNeeded = true;
 static volatile bool HaveCrashedWorker = false;
 
+/* set when signals arrive */
+static volatile sig_atomic_t pending_pm_pmsignal;
+static volatile sig_atomic_t pending_pm_child_exit;
+static volatile sig_atomic_t pending_pm_reload_request;
+static volatile sig_atomic_t pending_pm_shutdown_request;
+static volatile sig_atomic_t pending_pm_fast_shutdown_request;
+static volatile sig_atomic_t pending_pm_immediate_shutdown_request;
+
+/* I/O multiplexing object */
+static WaitEventSet *pm_wait_set;
+
 #ifdef USE_SSL
 /* Set when and if SSL has been initialized properly */
 static bool LoadedSSL = false;
@@ -380,10 +390,14 @@ static void getInstallationPaths(const char *argv0);
 static void checkControlFile(void);
 static Port *ConnCreate(int serverFd);
 static void ConnFree(Port *port);
-static void SIGHUP_handler(SIGNAL_ARGS);
-static void pmdie(SIGNAL_ARGS);
-static void reaper(SIGNAL_ARGS);
-static void sigusr1_handler(SIGNAL_ARGS);
+static void handle_pm_pmsignal_signal(SIGNAL_ARGS);
+static void handle_pm_child_exit_signal(SIGNAL_ARGS);
+static void handle_pm_reload_request_signal(SIGNAL_ARGS);
+static void handle_pm_shutdown_request_signal(SIGNAL_ARGS);
+static void process_pm_pmsignal(void);
+static void process_pm_child_exit(void);
+static void process_pm_reload_request(void);
+static void process_pm_shutdown_request(void);
 static void process_startup_packet_die(SIGNAL_ARGS);
 static void dummy_handler(SIGNAL_ARGS);
 static void StartupPacketTimeoutHandler(void);
@@ -401,7 +415,6 @@ static int	BackendStartup(Port *port);
 static int	ProcessStartupPacket(Port *port, bool ssl_done, bool gss_done);
 static void SendNegotiateProtocolVersion(List *unrecognized_protocol_options);
 static void processCancelRequest(Port *port, void *pkt);
-static int	initMasks(fd_set *rmask);
 static void report_fork_failure_to_client(Port *port, int errnum);
 static CAC_state canAcceptConnections(int backend_type);
 static bool RandomCancelKey(int32 *cancel_key);
@@ -609,26 +622,6 @@ PostmasterMain(int argc, char *argv[])
 	/*
 	 * Set up signal handlers for the postmaster process.
 	 *
-	 * In the postmaster, we use pqsignal_pm() rather than pqsignal() (which
-	 * is used by all child processes and client processes).  That has a
-	 * couple of special behaviors:
-	 *
-	 * 1. We tell sigaction() to block all signals for the duration of the
-	 * signal handler.  This is faster than our old approach of
-	 * blocking/unblocking explicitly in the signal handler, and it should also
-	 * prevent excessive stack consumption if signals arrive quickly.
-	 *
-	 * 2. We do not set the SA_RESTART flag.  This is because signals will be
-	 * blocked at all times except when ServerLoop is waiting for something to
-	 * happen, and during that window, we want signals to exit the select(2)
-	 * wait so that ServerLoop can respond if anything interesting happened.
-	 * On some platforms, signals marked SA_RESTART would not cause the
-	 * select() wait to end.
-	 *
-	 * Child processes will generally want SA_RESTART, so pqsignal() sets that
-	 * flag.  We expect children to set up their own handlers before
-	 * unblocking signals.
-	 *
 	 * CAUTION: when changing this list, check for side-effects on the signal
 	 * handling setup of child processes.  See tcop/postgres.c,
 	 * bootstrap/bootstrap.c, postmaster/bgwriter.c, postmaster/walwriter.c,
@@ -638,26 +631,19 @@ PostmasterMain(int argc, char *argv[])
 	pqinitmask();
 	PG_SETMASK(&BlockSig);
 
-	pqsignal_pm(SIGHUP, SIGHUP_handler);	/* reread config file and have
-											 * children do same */
-	pqsignal_pm(SIGINT, pmdie); /* send SIGTERM and shut down */
-	pqsignal_pm(SIGQUIT, pmdie);	/* send SIGQUIT and die */
-	pqsignal_pm(SIGTERM, pmdie);	/* wait for children and shut down */
-	pqsignal_pm(SIGALRM, SIG_IGN);	/* ignored */
-	pqsignal_pm(SIGPIPE, SIG_IGN);	/* ignored */
-	pqsignal_pm(SIGUSR1, sigusr1_handler);	/* message from child process */
-	pqsignal_pm(SIGUSR2, dummy_handler);	/* unused, reserve for children */
-	pqsignal_pm(SIGCHLD, reaper);	/* handle child termination */
-
-#ifdef SIGURG
+	pqsignal(SIGHUP, handle_pm_reload_request_signal);
+	pqsignal(SIGINT, handle_pm_shutdown_request_signal);
+	pqsignal(SIGQUIT, handle_pm_shutdown_request_signal);
+	pqsignal(SIGTERM, handle_pm_shutdown_request_signal);
+	pqsignal(SIGALRM, SIG_IGN); /* ignored */
+	pqsignal(SIGPIPE, SIG_IGN); /* ignored */
+	pqsignal(SIGUSR1, handle_pm_pmsignal_signal);
+	pqsignal(SIGUSR2, dummy_handler);	/* unused, reserve for children */
+	pqsignal(SIGCHLD, handle_pm_child_exit_signal);
 
-	/*
-	 * Ignore SIGURG for now.  Child processes may change this (see
-	 * InitializeLatchSupport), but they will not receive any such signals
-	 * until they wait on a latch.
-	 */
-	pqsignal_pm(SIGURG, SIG_IGN);	/* ignored */
-#endif
+	/* This may configure SIGURG, depending on platform. */
+	InitializeLatchSupport();
+	InitProcessLocalLatch();
 
 	/*
 	 * No other place in Postgres should touch SIGTTIN/SIGTTOU handling.  We
@@ -667,17 +653,20 @@ PostmasterMain(int argc, char *argv[])
 	 * child processes should just allow the inherited settings to stand.
 	 */
 #ifdef SIGTTIN
-	pqsignal_pm(SIGTTIN, SIG_IGN);	/* ignored */
+	pqsignal(SIGTTIN, SIG_IGN); /* ignored */
 #endif
 #ifdef SIGTTOU
-	pqsignal_pm(SIGTTOU, SIG_IGN);	/* ignored */
+	pqsignal(SIGTTOU, SIG_IGN); /* ignored */
 #endif
 
 	/* ignore SIGXFSZ, so that ulimit violations work like disk full */
 #ifdef SIGXFSZ
-	pqsignal_pm(SIGXFSZ, SIG_IGN);	/* ignored */
+	pqsignal(SIGXFSZ, SIG_IGN); /* ignored */
 #endif
 
+	/* Begin accepting signals. */
+	PG_SETMASK(&UnBlockSig);
+
 	/*
 	 * Options setup
 	 */
@@ -1698,105 +1687,107 @@ DetermineSleepTime(struct timeval *timeout)
 	}
 }
 
+/*
+ * Activate or deactivate notifications of server socket events.  Since we
+ * don't currently have a way to remove events from an existing WaitEventSet,
+ * we'll just destroy and recreate the whole thing.  This is called during
+ * shutdown so we can wait for backends to exit without accepting new
+ * connections, and during crash reinitialization when we need to start
+ * listening for new connections again.  This will be freed in fork children by
+ * ClosePostmasterPorts().
+ */
+static void
+ConfigurePostmasterWaitSet(bool accept_connections)
+{
+	int			nsockets;
+
+	if (pm_wait_set)
+		FreeWaitEventSet(pm_wait_set);
+	pm_wait_set = NULL;
+
+	/* How many server sockets do we need to wait for? */
+	nsockets = 0;
+	if (accept_connections)
+	{
+		while (nsockets < MAXLISTEN &&
+			   ListenSocket[nsockets] != PGINVALID_SOCKET)
+			++nsockets;
+	}
+
+	pm_wait_set = CreateWaitEventSet(CurrentMemoryContext, 1 + nsockets);
+	AddWaitEventToSet(pm_wait_set, WL_LATCH_SET, PGINVALID_SOCKET, MyLatch,
+					  NULL);
+
+	if (accept_connections)
+	{
+		for (int i = 0; i < nsockets; i++)
+			AddWaitEventToSet(pm_wait_set, WL_SOCKET_ACCEPT, ListenSocket[i],
+							  NULL, NULL);
+	}
+}
+
 /*
  * Main idle loop of postmaster
- *
- * NB: Needs to be called with signals blocked
  */
 static int
 ServerLoop(void)
 {
-	fd_set		readmask;
-	int			nSockets;
 	time_t		last_lockfile_recheck_time,
 				last_touch_time;
+	WaitEvent	events[MAXLISTEN];
+	int			nevents;
 
+	ConfigurePostmasterWaitSet(true);
 	last_lockfile_recheck_time = last_touch_time = time(NULL);
 
-	nSockets = initMasks(&readmask);
-
 	for (;;)
 	{
-		fd_set		rmask;
-		int			selres;
 		time_t		now;
+		struct timeval timeout;
 
-		/*
-		 * Wait for a connection request to arrive.
-		 *
-		 * We block all signals except while sleeping. That makes it safe for
-		 * signal handlers, which again block all signals while executing, to
-		 * do nontrivial work.
-		 *
-		 * If we are in PM_WAIT_DEAD_END state, then we don't want to accept
-		 * any new connections, so we don't call select(), and just sleep.
-		 */
-		memcpy((char *) &rmask, (char *) &readmask, sizeof(fd_set));
+		DetermineSleepTime(&timeout);
 
-		if (pmState == PM_WAIT_DEAD_END)
-		{
-			PG_SETMASK(&UnBlockSig);
-
-			pg_usleep(100000L); /* 100 msec seems reasonable */
-			selres = 0;
-
-			PG_SETMASK(&BlockSig);
-		}
-		else
-		{
-			/* must set timeout each time; some OSes change it! */
-			struct timeval timeout;
-
-			/* Needs to run with blocked signals! */
-			DetermineSleepTime(&timeout);
-
-			PG_SETMASK(&UnBlockSig);
-
-			selres = select(nSockets, &rmask, NULL, NULL, &timeout);
-
-			PG_SETMASK(&BlockSig);
-		}
-
-		/* Now check the select() result */
-		if (selres < 0)
-		{
-			if (errno != EINTR && errno != EWOULDBLOCK)
-			{
-				ereport(LOG,
-						(errcode_for_socket_access(),
-						 errmsg("select() failed in postmaster: %m")));
-				return STATUS_ERROR;
-			}
-		}
+		nevents = WaitEventSetWait(pm_wait_set,
+								   timeout.tv_sec * 1000 + timeout.tv_usec / 1000,
+								   events,
+								   lengthof(events),
+								   0 /* postmaster posts no wait_events */ );
 
 		/*
-		 * New connection pending on any of our sockets? If so, fork a child
-		 * process to deal with it.
+		 * Latch set by signal handler, or new connection pending on any of
+		 * our sockets? If the latter, fork a child process to deal with it.
 		 */
-		if (selres > 0)
+		for (int i = 0; i < nevents; i++)
 		{
-			int			i;
-
-			for (i = 0; i < MAXLISTEN; i++)
+			if (events[i].events & WL_LATCH_SET)
 			{
-				if (ListenSocket[i] == PGINVALID_SOCKET)
-					break;
-				if (FD_ISSET(ListenSocket[i], &rmask))
+				ResetLatch(MyLatch);
+
+				/* Process work requested via signal handlers. */
+				if (pending_pm_shutdown_request)
+					process_pm_shutdown_request();
+				if (pending_pm_child_exit)
+					process_pm_child_exit();
+				if (pending_pm_reload_request)
+					process_pm_reload_request();
+				if (pending_pm_pmsignal)
+					process_pm_pmsignal();
+			}
+			else if (events[i].events & WL_SOCKET_ACCEPT)
+			{
+				Port	   *port;
+
+				port = ConnCreate(events[i].fd);
+				if (port)
 				{
-					Port	   *port;
+					BackendStartup(port);
 
-					port = ConnCreate(ListenSocket[i]);
-					if (port)
-					{
-						BackendStartup(port);
-
-						/*
-						 * We no longer need the open socket or port structure
-						 * in this process
-						 */
-						StreamClose(port->sock);
-						ConnFree(port);
-					}
+					/*
+					 * We no longer need the open socket or port structure in
+					 * this process
+					 */
+					StreamClose(port->sock);
+					ConnFree(port);
 				}
 			}
 		}
@@ -1939,34 +1930,6 @@ ServerLoop(void)
 	}
 }
 
-/*
- * Initialise the masks for select() for the ports we are listening on.
- * Return the number of sockets to listen on.
- */
-static int
-initMasks(fd_set *rmask)
-{
-	int			maxsock = -1;
-	int			i;
-
-	FD_ZERO(rmask);
-
-	for (i = 0; i < MAXLISTEN; i++)
-	{
-		int			fd = ListenSocket[i];
-
-		if (fd == PGINVALID_SOCKET)
-			break;
-		FD_SET(fd, rmask);
-
-		if (fd > maxsock)
-			maxsock = fd;
-	}
-
-	return maxsock + 1;
-}
-
-
 /*
  * Read a client's startup packet and do something according to it.
  *
@@ -2609,6 +2572,10 @@ ClosePostmasterPorts(bool am_syslogger)
 {
 	int			i;
 
+	/* Release resources held by the postmaster's WaitEventSet. */
+	if (pm_wait_set)
+		FreeWaitEventSetAfterFork(pm_wait_set);
+
 #ifndef WIN32
 
 	/*
@@ -2707,15 +2674,46 @@ InitProcessGlobals(void)
 #endif
 }
 
+/*
+ * Child processes use SIGUSR1 to notify us of 'pmsignals'.  pg_ctl uses
+ * SIGUSR1 to ask postmaster to check for logrotate and promote files.
+ */
+static void
+handle_pm_pmsignal_signal(SIGNAL_ARGS)
+{
+	int			save_errno = errno;
+
+	pending_pm_pmsignal = true;
+	SetLatch(MyLatch);
+
+	errno = save_errno;
+}
 
 /*
- * SIGHUP -- reread config files, and tell children to do same
+ * pg_ctl uses SIGHUP to request a reload of the configuration files.
  */
 static void
-SIGHUP_handler(SIGNAL_ARGS)
+handle_pm_reload_request_signal(SIGNAL_ARGS)
 {
 	int			save_errno = errno;
 
+	pending_pm_reload_request = true;
+	SetLatch(MyLatch);
+
+	errno = save_errno;
+}
+
+/*
+ * Re-read config files, and tell children to do same.
+ */
+static void
+process_pm_reload_request(void)
+{
+	pending_pm_reload_request = false;
+
+	ereport(DEBUG2,
+			(errmsg_internal("postmaster received reload request signal")));
+
 	if (Shutdown <= SmartShutdown)
 	{
 		ereport(LOG,
@@ -2771,26 +2769,71 @@ SIGHUP_handler(SIGNAL_ARGS)
 		write_nondefault_variables(PGC_SIGHUP);
 #endif
 	}
+}
+
+/*
+ * pg_ctl uses SIGTERM, SIGINT and SIGQUIT to request different types of
+ * shutdown.
+ */
+static void
+handle_pm_shutdown_request_signal(SIGNAL_ARGS)
+{
+	int			save_errno = errno;
+
+	switch (postgres_signal_arg)
+	{
+		case SIGTERM:
+			/* smart is implied if the other two flags aren't set */
+			pending_pm_shutdown_request = true;
+			break;
+		case SIGINT:
+			pending_pm_fast_shutdown_request = true;
+			pending_pm_shutdown_request = true;
+			break;
+		case SIGQUIT:
+			pending_pm_immediate_shutdown_request = true;
+			pending_pm_shutdown_request = true;
+			break;
+	}
+	SetLatch(MyLatch);
 
 	errno = save_errno;
 }
 
-
 /*
- * pmdie -- signal handler for processing various postmaster signals.
+ * Process shutdown request.
  */
 static void
-pmdie(SIGNAL_ARGS)
+process_pm_shutdown_request(void)
 {
-	int			save_errno = errno;
+	int			mode;
 
 	ereport(DEBUG2,
-			(errmsg_internal("postmaster received signal %d",
-							 postgres_signal_arg)));
+			(errmsg_internal("postmaster received shutdown request signal")));
 
-	switch (postgres_signal_arg)
+	pending_pm_shutdown_request = false;
+
+	/*
+	 * If more than one shutdown request signal arrived since the last server
+	 * loop, take the one that is the most immediate.  That matches the
+	 * priority that would apply if we processed them one by one in any order.
+	 */
+	if (pending_pm_immediate_shutdown_request)
 	{
-		case SIGTERM:
+		pending_pm_immediate_shutdown_request = false;
+		mode = ImmediateShutdown;
+	}
+	else if (pending_pm_fast_shutdown_request)
+	{
+		pending_pm_fast_shutdown_request = false;
+		mode = FastShutdown;
+	}
+	else
+		mode = SmartShutdown;
+
+	switch (mode)
+	{
+		case SmartShutdown:
 
 			/*
 			 * Smart Shutdown:
@@ -2830,7 +2873,7 @@ pmdie(SIGNAL_ARGS)
 			PostmasterStateMachine();
 			break;
 
-		case SIGINT:
+		case FastShutdown:
 
 			/*
 			 * Fast Shutdown:
@@ -2871,7 +2914,7 @@ pmdie(SIGNAL_ARGS)
 			PostmasterStateMachine();
 			break;
 
-		case SIGQUIT:
+		case ImmediateShutdown:
 
 			/*
 			 * Immediate Shutdown:
@@ -2908,20 +2951,30 @@ pmdie(SIGNAL_ARGS)
 			PostmasterStateMachine();
 			break;
 	}
+}
+
+static void
+handle_pm_child_exit_signal(SIGNAL_ARGS)
+{
+	int			save_errno = errno;
+
+	pending_pm_child_exit = true;
+	SetLatch(MyLatch);
 
 	errno = save_errno;
 }
 
 /*
- * Reaper -- signal handler to cleanup after a child process dies.
+ * Cleanup after a child process dies.
  */
 static void
-reaper(SIGNAL_ARGS)
+process_pm_child_exit(void)
 {
-	int			save_errno = errno;
 	int			pid;			/* process id of dead child process */
 	int			exitstatus;		/* its exit status */
 
+	pending_pm_child_exit = false;
+
 	ereport(DEBUG4,
 			(errmsg_internal("reaping dead processes")));
 
@@ -3213,8 +3266,6 @@ reaper(SIGNAL_ARGS)
 	 * or actions to make.
 	 */
 	PostmasterStateMachine();
-
-	errno = save_errno;
 }
 
 /*
@@ -3642,8 +3693,9 @@ LogChildExit(int lev, const char *procname, int pid, int exitstatus)
 /*
  * Advance the postmaster's state machine and take actions as appropriate
  *
- * This is common code for pmdie(), reaper() and sigusr1_handler(), which
- * receive the signals that might mean we need to change state.
+ * This is common code for process_shutdown_request(), process_child_exit() and
+ * process_pmsignal(), which process the signals that might mean we need
+ * to change state.
  */
 static void
 PostmasterStateMachine(void)
@@ -3796,6 +3848,9 @@ PostmasterStateMachine(void)
 
 	if (pmState == PM_WAIT_DEAD_END)
 	{
+		/* Don't allow any new socket connection events. */
+		ConfigurePostmasterWaitSet(false);
+
 		/*
 		 * PM_WAIT_DEAD_END state ends when the BackendList is entirely empty
 		 * (ie, no dead_end children remain), and the archiver is gone too.
@@ -3905,6 +3960,9 @@ PostmasterStateMachine(void)
 		pmState = PM_STARTUP;
 		/* crash recovery started, reset SIGKILL flag */
 		AbortStartTime = 0;
+
+		/* start accepting server socket connection events again */
+		ConfigurePostmasterWaitSet(true);
 	}
 }
 
@@ -5013,12 +5071,16 @@ ExitPostmaster(int status)
 }
 
 /*
- * sigusr1_handler - handle signal conditions from child processes
+ * Handle pmsignal conditions representing requests from backends,
+ * and check for promote and logrotate requests from pg_ctl.
  */
 static void
-sigusr1_handler(SIGNAL_ARGS)
+process_pm_pmsignal(void)
 {
-	int			save_errno = errno;
+	pending_pm_pmsignal = false;
+
+	ereport(DEBUG2,
+			(errmsg_internal("postmaster received action request signal")));
 
 	/*
 	 * RECOVERY_STARTED and BEGIN_HOT_STANDBY signals are ignored in
@@ -5159,8 +5221,6 @@ sigusr1_handler(SIGNAL_ARGS)
 		 */
 		signal_child(StartupPID, SIGUSR2);
 	}
-
-	errno = save_errno;
 }
 
 /*
diff --git a/src/backend/tcop/postgres.c b/src/backend/tcop/postgres.c
index 224ab290af..470b734e9e 100644
--- a/src/backend/tcop/postgres.c
+++ b/src/backend/tcop/postgres.c
@@ -24,7 +24,6 @@
 #include <signal.h>
 #include <unistd.h>
 #include <sys/resource.h>
-#include <sys/select.h>
 #include <sys/socket.h>
 #include <sys/time.h>
 
diff --git a/src/backend/utils/init/miscinit.c b/src/backend/utils/init/miscinit.c
index 9b840a6318..0cdc1e11a3 100644
--- a/src/backend/utils/init/miscinit.c
+++ b/src/backend/utils/init/miscinit.c
@@ -135,8 +135,7 @@ InitPostmasterChild(void)
 
 	/* Initialize process-local latch support */
 	InitializeLatchSupport();
-	MyLatch = &LocalLatchData;
-	InitLatch(MyLatch);
+	InitProcessLocalLatch();
 	InitializeLatchWaitSet();
 
 	/*
@@ -189,8 +188,7 @@ InitStandaloneProcess(const char *argv0)
 
 	/* Initialize process-local latch support */
 	InitializeLatchSupport();
-	MyLatch = &LocalLatchData;
-	InitLatch(MyLatch);
+	InitProcessLocalLatch();
 	InitializeLatchWaitSet();
 
 	/*
@@ -232,6 +230,13 @@ SwitchToSharedLatch(void)
 	SetLatch(MyLatch);
 }
 
+void
+InitProcessLocalLatch(void)
+{
+	MyLatch = &LocalLatchData;
+	InitLatch(MyLatch);
+}
+
 void
 SwitchBackToLocalLatch(void)
 {
diff --git a/src/include/libpq/pqsignal.h b/src/include/libpq/pqsignal.h
index 29ee5ad2b6..1e66f25b76 100644
--- a/src/include/libpq/pqsignal.h
+++ b/src/include/libpq/pqsignal.h
@@ -53,7 +53,4 @@ extern PGDLLIMPORT sigset_t StartupBlockSig;
 
 extern void pqinitmask(void);
 
-/* pqsigfunc is declared in src/include/port.h */
-extern pqsigfunc pqsignal_pm(int signo, pqsigfunc func);
-
 #endif							/* PQSIGNAL_H */
diff --git a/src/include/miscadmin.h b/src/include/miscadmin.h
index 0ffeefc437..96b3a1e1a0 100644
--- a/src/include/miscadmin.h
+++ b/src/include/miscadmin.h
@@ -310,6 +310,7 @@ extern PGDLLIMPORT char *DatabasePath;
 /* now in utils/init/miscinit.c */
 extern void InitPostmasterChild(void);
 extern void InitStandaloneProcess(const char *argv0);
+extern void InitProcessLocalLatch(void);
 extern void SwitchToSharedLatch(void);
 extern void SwitchBackToLocalLatch(void);
 
-- 
2.38.1