Age Owner Branch data TLA Line data Source code
1 : : /*
2 : : * fork_process.c
3 : : * A simple wrapper on top of fork(). This does not handle the
4 : : * EXEC_BACKEND case; it might be extended to do so, but it would be
5 : : * considerably more complex.
6 : : *
7 : : * Copyright (c) 1996-2024, PostgreSQL Global Development Group
8 : : *
9 : : * IDENTIFICATION
10 : : * src/backend/postmaster/fork_process.c
11 : : */
12 : : #include "postgres.h"
13 : :
14 : : #include <fcntl.h>
15 : : #include <signal.h>
16 : : #include <time.h>
17 : : #include <sys/stat.h>
18 : : #include <sys/time.h>
19 : : #include <unistd.h>
20 : :
21 : : #include "libpq/pqsignal.h"
22 : : #include "postmaster/fork_process.h"
23 : :
24 : : #ifndef WIN32
25 : : /*
26 : : * Wrapper for fork(). Return values are the same as those for fork():
27 : : * -1 if the fork failed, 0 in the child process, and the PID of the
28 : : * child in the parent process. Signals are blocked while forking, so
29 : : * the child must unblock.
30 : : */
31 : : pid_t
6975 neilc@samurai.com 32 :CBC 19834 : fork_process(void)
33 : : {
34 : : pid_t result;
35 : : const char *oomfilename;
36 : : sigset_t save_mask;
37 : :
38 : : #ifdef LINUX_PROFILE
39 : : struct itimerval prof_itimer;
40 : : #endif
41 : :
42 : : /*
43 : : * Flush stdio channels just before fork, to avoid double-output problems.
44 : : */
594 tgl@sss.pgh.pa.us 45 : 19834 : fflush(NULL);
46 : :
47 : : #ifdef LINUX_PROFILE
48 : :
49 : : /*
50 : : * Linux's fork() resets the profiling timer in the child process. If we
51 : : * want to profile child processes then we need to save and restore the
52 : : * timer setting. This is a waste of time if not profiling, however, so
53 : : * only do it if commanded by specific -DLINUX_PROFILE switch.
54 : : */
55 : : getitimer(ITIMER_PROF, &prof_itimer);
56 : : #endif
57 : :
58 : : /*
59 : : * We start postmaster children with signals blocked. This allows them to
60 : : * install their own handlers before unblocking, to avoid races where they
61 : : * might run the postmaster's handler and miss an important control
62 : : * signal. With more analysis this could potentially be relaxed.
63 : : */
458 tmunro@postgresql.or 64 : 19834 : sigprocmask(SIG_SETMASK, &BlockSig, &save_mask);
6975 neilc@samurai.com 65 : 19834 : result = fork();
6674 bruce@momjian.us 66 [ + + ]: 39527 : if (result == 0)
67 : : {
68 : : /* fork succeeded, in child */
69 : : #ifdef LINUX_PROFILE
70 : : setitimer(ITIMER_PROF, &prof_itimer, NULL);
71 : : #endif
72 : :
73 : : /*
74 : : * By default, Linux tends to kill the postmaster in out-of-memory
75 : : * situations, because it blames the postmaster for the sum of child
76 : : * process sizes *including shared memory*. (This is unbelievably
77 : : * stupid, but the kernel hackers seem uninterested in improving it.)
78 : : * Therefore it's often a good idea to protect the postmaster by
79 : : * setting its OOM score adjustment negative (which has to be done in
80 : : * a root-owned startup script). Since the adjustment is inherited by
81 : : * child processes, this would ordinarily mean that all the
82 : : * postmaster's children are equally protected against OOM kill, which
83 : : * is not such a good idea. So we provide this code to allow the
84 : : * children to change their OOM score adjustments again. Both the
85 : : * file name to write to and the value to write are controlled by
86 : : * environment variables, which can be set by the same startup script
87 : : * that did the original adjustment.
88 : : */
3588 tgl@sss.pgh.pa.us 89 : 19693 : oomfilename = getenv("PG_OOM_ADJUST_FILE");
90 : :
91 [ - + ]: 19693 : if (oomfilename != NULL)
92 : : {
93 : : /*
94 : : * Use open() not stdio, to ensure we control the open flags. Some
95 : : * Linux security environments reject anything but O_WRONLY.
96 : : */
3588 tgl@sss.pgh.pa.us 97 :UBC 0 : int fd = open(oomfilename, O_WRONLY, 0);
98 : :
99 : : /* We ignore all errors */
5207 100 [ # # ]: 0 : if (fd >= 0)
101 : : {
3588 102 : 0 : const char *oomvalue = getenv("PG_OOM_ADJUST_VALUE");
103 : : int rc;
104 : :
105 [ # # ]: 0 : if (oomvalue == NULL) /* supply a useful default */
106 : 0 : oomvalue = "0";
107 : :
108 : 0 : rc = write(fd, oomvalue, strlen(oomvalue));
109 : : (void) rc;
5207 110 : 0 : close(fd);
111 : : }
112 : : }
113 : :
114 : : /* do post-fork initialization for random number generation */
1255 magnus@hagander.net 115 :CBC 19693 : pg_strong_random_init();
116 : : }
117 : : else
118 : : {
119 : : /* in parent, restore signal mask */
458 tmunro@postgresql.or 120 : 19834 : sigprocmask(SIG_SETMASK, &save_mask, NULL);
121 : : }
122 : :
6975 neilc@samurai.com 123 : 39527 : return result;
124 : : }
125 : :
126 : : #endif /* ! WIN32 */
|
