Adding upstream version 16.2.upstream/16.2

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 126 insertions, 0 deletions

diff --git a/src/backend/postmaster/fork_process.c b/src/backend/postmaster/fork_process.c
new file mode 100644
index 0000000..6f9c276
--- /dev/null
+++ b/src/backend/postmaster/fork_process.c
@@ -0,0 +1,126 @@
+/*
+ * fork_process.c
+ *	 A simple wrapper on top of fork(). This does not handle the
+ *	 EXEC_BACKEND case; it might be extended to do so, but it would be
+ *	 considerably more complex.
+ *
+ * Copyright (c) 1996-2023, PostgreSQL Global Development Group
+ *
+ * IDENTIFICATION
+ *	  src/backend/postmaster/fork_process.c
+ */
+#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.  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;
+#endif
+
+	/*
+	 * Flush stdio channels just before fork, to avoid double-output problems.
+	 */
+	fflush(NULL);
+
+#ifdef LINUX_PROFILE
+
+	/*
+	 * Linux's fork() resets the profiling timer in the child process. If we
+	 * want to profile child processes then we need to save and restore the
+	 * timer setting.  This is a waste of time if not profiling, however, so
+	 * only do it if commanded by specific -DLINUX_PROFILE switch.
+	 */
+	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)
+	{
+		/* fork succeeded, in child */
+#ifdef LINUX_PROFILE
+		setitimer(ITIMER_PROF, &prof_itimer, NULL);
+#endif
+
+		/*
+		 * By default, Linux tends to kill the postmaster in out-of-memory
+		 * situations, because it blames the postmaster for the sum of child
+		 * process sizes *including shared memory*.  (This is unbelievably
+		 * stupid, but the kernel hackers seem uninterested in improving it.)
+		 * Therefore it's often a good idea to protect the postmaster by
+		 * setting its OOM score adjustment negative (which has to be done in
+		 * a root-owned startup script).  Since the adjustment is inherited by
+		 * child processes, this would ordinarily mean that all the
+		 * postmaster's children are equally protected against OOM kill, which
+		 * is not such a good idea.  So we provide this code to allow the
+		 * children to change their OOM score adjustments again.  Both the
+		 * file name to write to and the value to write are controlled by
+		 * environment variables, which can be set by the same startup script
+		 * that did the original adjustment.
+		 */
+		oomfilename = getenv("PG_OOM_ADJUST_FILE");
+
+		if (oomfilename != NULL)
+		{
+			/*
+			 * Use open() not stdio, to ensure we control the open flags. Some
+			 * Linux security environments reject anything but O_WRONLY.
+			 */
+			int			fd = open(oomfilename, O_WRONLY, 0);
+
+			/* We ignore all errors */
+			if (fd >= 0)
+			{
+				const char *oomvalue = getenv("PG_OOM_ADJUST_VALUE");
+				int			rc;
+
+				if (oomvalue == NULL)	/* supply a useful default */
+					oomvalue = "0";
+
+				rc = write(fd, oomvalue, strlen(oomvalue));
+				(void) rc;
+				close(fd);
+			}
+		}
+
+		/* 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;
+}
+
+#endif							/* ! WIN32 */