Author: hrs
Date: Sat Dec 31 06:23:05 2016
New Revision: 310890
URL: https://svnweb.freebsd.org/changeset/base/310890
Log:
Replace two fat signal handlers with function calls in
the main I/O multiplex loop. select() now watches
a pipe which is written by the new skinny signal
handlers and the received signals are handled inside
the loop sequencially.
This eliminates a complex signal mask to guarantee
async-signal safety.
Modified:
head/usr.sbin/syslogd/syslogd.c
Modified: head/usr.sbin/syslogd/syslogd.c
==============================================================================
--- head/usr.sbin/syslogd/syslogd.c Sat Dec 31 06:07:48 2016
(r310889)
+++ head/usr.sbin/syslogd/syslogd.c Sat Dec 31 06:23:05 2016
(r310890)
@@ -321,8 +321,9 @@ static int LogFacPri; /* Put facility an
static int KeepKernFac; /* Keep remotely logged kernel facility */
static int needdofsync = 0; /* Are any file(s) waiting to be fsynced? */
static struct pidfh *pfh;
+static int sigp[2]; /* Pipe to catch a signal during select(). */
-static volatile sig_atomic_t MarkSet, WantDie;
+static volatile sig_atomic_t MarkSet, WantDie, WantInitialize, WantReapchild;
static int allowaddr(char *);
static int addfile(struct filed *);
@@ -340,6 +341,7 @@ static void dofsync(void);
static void domark(int);
static void fprintlog(struct filed *, int, const char *);
static void init(int);
+static void init_sh(int);
static void logerror(const char *);
static void logmsg(int, const char *, const char *, int);
static void log_deadchild(pid_t, int, const char *);
@@ -347,11 +349,13 @@ static void markit(void);
static int socksetup(struct peer *);
static int socklist_recv_file(struct socklist *);
static int socklist_recv_sock(struct socklist *);
+static int socklist_recv_signal(struct socklist *);
static int skip_message(const char *, const char *, int);
static void printline(const char *, char *, int);
static void printsys(char *);
static int p_open(const char *, pid_t *);
static void reapchild(int);
+static void reapchild_sh(int);
static const char *ttymsg_check(struct iovec *, int, char *, int);
static void usage(void);
static int validate(struct sockaddr *, const char *);
@@ -435,7 +439,6 @@ main(int argc, char *argv[])
struct timeval tv, *tvp;
struct peer *pe;
struct socklist *sl;
- sigset_t mask;
pid_t ppid = 1, spid;
char *p;
@@ -578,6 +581,17 @@ main(int argc, char *argv[])
if ((argc -= optind) != 0)
usage();
+ /* Pipe to catch a signal during select(). */
+ s = pipe2(sigp, O_NONBLOCK);
+ if (s < 0) {
+ err(1, "cannot open a pipe for signals");
+ } else {
+ addsock(NULL, 0, &(struct socklist){
+ .sl_socket = sigp[1],
+ .sl_recv = socklist_recv_signal
+ });
+ }
+
/* Listen by default: /dev/klog. */
s = open(_PATH_KLOG, O_RDONLY|O_NONBLOCK, 0);
if (s < 0) {
@@ -632,19 +646,8 @@ main(int argc, char *argv[])
(void)signal(SIGTERM, dodie);
(void)signal(SIGINT, Debug ? dodie : SIG_IGN);
(void)signal(SIGQUIT, Debug ? dodie : SIG_IGN);
- /*
- * We don't want the SIGCHLD and SIGHUP handlers to interfere
- * with each other; they are likely candidates for being called
- * simultaneously (SIGHUP closes pipe descriptor, process dies,
- * SIGCHLD happens).
- */
- sigemptyset(&mask);
- sigaddset(&mask, SIGHUP);
- (void)sigaction(SIGCHLD, &(struct sigaction){
- .sa_handler = reapchild,
- .sa_mask = mask,
- .sa_flags = SA_RESTART
- }, NULL);
+ (void)signal(SIGHUP, init_sh);
+ (void)signal(SIGCHLD, reapchild_sh);
(void)signal(SIGALRM, domark);
(void)signal(SIGPIPE, SIG_IGN); /* We'll catch EPIPE instead. */
(void)alarm(TIMERINTVL);
@@ -654,16 +657,6 @@ main(int argc, char *argv[])
dprintf("off & running....\n");
- init(0);
- /* prevent SIGHUP and SIGCHLD handlers from running in parallel */
- sigemptyset(&mask);
- sigaddset(&mask, SIGCHLD);
- (void)sigaction(SIGHUP, &(struct sigaction){
- .sa_handler = init,
- .sa_mask = mask,
- .sa_flags = SA_RESTART
- }, NULL);
-
tvp = &tv;
tv.tv_sec = tv.tv_usec = 0;
@@ -677,6 +670,12 @@ main(int argc, char *argv[])
errx(1, "calloc fd_set");
for (;;) {
+ if (Initialized == 0)
+ init(0);
+ else if (WantInitialize)
+ init(WantInitialize);
+ if (WantReapchild)
+ reapchild(WantReapchild);
if (MarkSet)
markit();
if (WantDie)
@@ -716,6 +715,19 @@ main(int argc, char *argv[])
}
static int
+socklist_recv_signal(struct socklist *sl __unused)
+{
+ ssize_t len;
+ static char buf[BUFSIZ];
+
+ /* Clear an wake-up signal by reading dummy data. */
+ while ((len = read(sigp[0], buf, sizeof(buf))) > 0)
+ ;
+
+ return (0);
+}
+
+static int
socklist_recv_sock(struct socklist *sl)
{
struct sockaddr_storage ss;
@@ -987,7 +999,7 @@ static void
logmsg(int pri, const char *msg, const char *from, int flags)
{
struct filed *f;
- int i, fac, msglen, omask, prilev;
+ int i, fac, msglen, prilev;
const char *timestamp;
char prog[NAME_MAX+1];
char buf[MAXLINE+1];
@@ -995,8 +1007,6 @@ logmsg(int pri, const char *msg, const c
dprintf("logmsg: pri %o, flags %x, from %s, msg %s\n",
pri, flags, from, msg);
- omask = sigblock(sigmask(SIGHUP)|sigmask(SIGALRM));
-
/*
* Check to see if msg looks non-standard.
*/
@@ -1027,10 +1037,8 @@ logmsg(int pri, const char *msg, const c
fac = LOG_FAC(pri);
/* Check maximum facility number. */
- if (fac > LOG_NFACILITIES) {
- (void)sigsetmask(omask);
+ if (fac > LOG_NFACILITIES)
return;
- }
prilev = LOG_PRI(pri);
@@ -1067,7 +1075,6 @@ logmsg(int pri, const char *msg, const c
close(f->f_file);
f->f_file = -1;
}
- (void)sigsetmask(omask);
return;
}
STAILQ_FOREACH(f, &fhead, next) {
@@ -1139,7 +1146,6 @@ logmsg(int pri, const char *msg, const c
}
}
}
- (void)sigsetmask(omask);
}
static void
@@ -1507,6 +1513,17 @@ ttymsg_check(struct iovec *iov, int iovc
}
static void
+reapchild_sh(int signo)
+{
+ static char buf[BUFSIZ];
+
+ WantReapchild = signo;
+ /* Send an wake-up signal to the select() loop. */
+ read(sigp[0], buf, sizeof(buf));
+ write(sigp[1], &signo, sizeof(signo));
+}
+
+static void
reapchild(int signo __unused)
{
int status;
@@ -1514,10 +1531,6 @@ reapchild(int signo __unused)
struct filed *f;
while ((pid = wait3(&status, WNOHANG, (struct rusage *)NULL)) > 0) {
- if (!Initialized)
- /* Don't tell while we are initting. */
- continue;
-
/* First, look if it's a process from the dead queue. */
if (deadq_removebypid(pid))
continue;
@@ -1532,6 +1545,7 @@ reapchild(int signo __unused)
}
}
}
+ WantReapchild = 0;
}
/*
@@ -1541,7 +1555,6 @@ static const char *
cvthname(struct sockaddr *f)
{
int error, hl;
- sigset_t omask, nmask;
static char hname[NI_MAXHOST], ip[NI_MAXHOST];
dprintf("cvthname(%d) len = %d\n", f->sa_family, f->sa_len);
@@ -1556,12 +1569,8 @@ cvthname(struct sockaddr *f)
if (!resolve)
return (ip);
- sigemptyset(&nmask);
- sigaddset(&nmask, SIGHUP);
- sigprocmask(SIG_BLOCK, &nmask, &omask);
error = getnameinfo(f, f->sa_len, hname, sizeof(hname),
NULL, 0, NI_NAMEREQD);
- sigprocmask(SIG_SETMASK, &omask, NULL);
if (error) {
dprintf("Host name for your address (%s) unknown\n", ip);
return (ip);
@@ -1616,11 +1625,8 @@ die(int signo)
{
struct filed *f;
struct socklist *sl;
- int was_initialized;
char buf[100];
- was_initialized = Initialized;
- Initialized = 0; /* Don't log SIGCHLDs. */
STAILQ_FOREACH(f, &fhead, next) {
/* flush any pending output */
if (f->f_prevcount)
@@ -1628,7 +1634,6 @@ die(int signo)
if (f->f_type == F_PIPE && f->fu_pipe_pid > 0)
close_filed(f);
}
- Initialized = was_initialized;
if (signo) {
dprintf("syslogd: exiting on signal %d\n", signo);
(void)snprintf(buf, sizeof(buf), "exiting on signal %d", signo);
@@ -1793,6 +1798,17 @@ readconfigfile(FILE *cf, int allow_inclu
* INIT -- Initialize syslogd from configuration table
*/
static void
+init_sh(int signo)
+{
+ static char buf[BUFSIZ];
+
+ WantInitialize = signo;
+ /* Send an wake-up signal to the select() loop. */
+ read(sigp[0], buf, sizeof(buf));
+ write(sigp[1], &signo, sizeof(signo));
+}
+
+static void
init(int signo)
{
int i;
@@ -1804,6 +1820,7 @@ init(int signo)
char bootfileMsg[LINE_MAX];
dprintf("init\n");
+ WantInitialize = 0;
/*
* Load hostname (may have changed).
@@ -2669,7 +2686,6 @@ p_open(const char *prog, pid_t *rpid)
{
int pfd[2], nulldesc;
pid_t pid;
- sigset_t omask, mask;
char *argv[4]; /* sh -c cmd NULL */
char errmsg[200];
@@ -2679,17 +2695,13 @@ p_open(const char *prog, pid_t *rpid)
/* we are royally screwed anyway */
return (-1);
- sigemptyset(&mask);
- sigaddset(&mask, SIGALRM);
- sigaddset(&mask, SIGHUP);
- sigprocmask(SIG_BLOCK, &mask, &omask);
switch ((pid = fork())) {
case -1:
- sigprocmask(SIG_SETMASK, &omask, 0);
close(nulldesc);
return (-1);
case 0:
+ (void)setsid(); /* Avoid catching SIGHUPs. */
argv[0] = strdup("sh");
argv[1] = strdup("-c");
argv[2] = strdup(prog);
@@ -2700,19 +2712,11 @@ p_open(const char *prog, pid_t *rpid)
}
alarm(0);
- (void)setsid(); /* Avoid catching SIGHUPs. */
- /*
- * Throw away pending signals, and reset signal
- * behaviour to standard values.
- */
- signal(SIGALRM, SIG_IGN);
- signal(SIGHUP, SIG_IGN);
- sigprocmask(SIG_SETMASK, &omask, 0);
- signal(SIGPIPE, SIG_DFL);
- signal(SIGQUIT, SIG_DFL);
- signal(SIGALRM, SIG_DFL);
- signal(SIGHUP, SIG_DFL);
+ /* Restore signals marked as SIG_IGN. */
+ (void)signal(SIGINT, SIG_DFL);
+ (void)signal(SIGQUIT, SIG_DFL);
+ (void)signal(SIGPIPE, SIG_DFL);
dup2(pfd[0], STDIN_FILENO);
dup2(nulldesc, STDOUT_FILENO);
@@ -2722,8 +2726,6 @@ p_open(const char *prog, pid_t *rpid)
(void)execvp(_PATH_BSHELL, argv);
_exit(255);
}
-
- sigprocmask(SIG_SETMASK, &omask, 0);
close(nulldesc);
close(pfd[0]);
/*
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