[PATCH v2] git daemon: avoid calling syslog() from a signal handler
Signal handlers should never call syslog(), as that can raise signals of its own.
Instead, call the syslog() from the master process.
To avoid waking up unnecessarily, a pipe is set up that is only ever written to by child_handler(), when a child disconnects, as suggested per Junio.
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
---
On Sat, 5 Jul 2008, Junio C Hamano wrote:
> Johannes Schindelin <Johannes.Schindelin@gmx.de> writes:
>
> > Junio wrote:
> >> Another way would be to set up a pipe to ourself that is
> >> included in the poll() and write a byte to the pipe from the signal
> >> handler.
> >
> > It still would need to break out of the poll(), in which case
> > the effect would be _exactly_ the same,...
>
> I do not think so.
Okay.
Note that we still have to check for dead children in
check_max_connections(), and since child_handler() knows nothing
about that, it still will write to the pipe, waking up the loop
unnecessarily.
But that will be rare.
This is no longer as trivial as I wanted it to be, so I'd
appreciate a few eyeballs on this patch.
daemon.c | 69 +++++++++++++++++++++++++++++++++++++++++++------------------
1 files changed, 48 insertions(+), 21 deletions(-)
diff --git a/daemon.c b/daemon.c
index 63cd12c..620a288 100644
--- a/daemon.c
+++ b/daemon.c
@@ -16,6 +16,7 @@
static int log_syslog;
static int verbose;
static int reuseaddr;
+static int child_handler_pipe[2];
static const char daemon_usage[] =
"git-daemon [--verbose] [--syslog] [--export-all]\n"
@@ -694,23 +695,47 @@ static void kill_some_children(int signo, unsigned start, unsigned stop)
}
}
+static void check_dead_children(void)
+{
+ unsigned spawned, reaped, deleted;
+
+ spawned = children_spawned;
+ reaped = children_reaped;
+ deleted = children_deleted;
+
+ while (deleted < reaped) {
+ pid_t pid = dead_child[deleted % MAX_CHILDREN];
+ const char *dead = pid < 0 ? " (with error)" : "";
+
+ if (pid < 0)
+ pid = -pid;
+
+ /* XXX: Custom logging, since we don't wanna getpid() */
+ if (verbose) {
+ if (log_syslog)
+ syslog(LOG_INFO, "[%d] Disconnected%s",
+ pid, dead);
+ else
+ fprintf(stderr, "[%d] Disconnected%s\n",
+ pid, dead);
+ }
+ remove_child(pid, deleted, spawned);
+ deleted++;
+ }
+ children_deleted = deleted;
+}
+
static void check_max_connections(void)
{
for (;;) {
int active;
- unsigned spawned, reaped, deleted;
+ unsigned spawned, deleted;
+
+ check_dead_children();
spawned = children_spawned;
- reaped = children_reaped;
deleted = children_deleted;
- while (deleted < reaped) {
- pid_t pid = dead_child[deleted % MAX_CHILDREN];
- remove_child(pid, deleted, spawned);
- deleted++;
- }
- children_deleted = deleted;
-
active = spawned - deleted;
if (active <= max_connections)
break;
@@ -760,18 +785,11 @@ static void child_handler(int signo)
if (pid > 0) {
unsigned reaped = children_reaped;
+ if (!WIFEXITED(status) || WEXITSTATUS(status) > 0)
+ pid = -pid;
dead_child[reaped % MAX_CHILDREN] = pid;
children_reaped = reaped + 1;
- /* XXX: Custom logging, since we don't wanna getpid() */
- if (verbose) {
- const char *dead = "";
- if (!WIFEXITED(status) || WEXITSTATUS(status) > 0)
- dead = " (with error)";
- if (log_syslog)
- syslog(LOG_INFO, "[%d] Disconnected%s", pid, dead);
- else
- fprintf(stderr, "[%d] Disconnected%s\n", pid, dead);
- }
+ write(child_handler_pipe[1], &status, 1);
continue;
}
break;
@@ -917,19 +935,24 @@ static int service_loop(int socknum, int *socklist)
struct pollfd *pfd;
int i;
- pfd = xcalloc(socknum, sizeof(struct pollfd));
+ if (pipe(child_handler_pipe) < 0)
+ die ("Could not set up pipe for child handler");
+
+ pfd = xcalloc(socknum + 1, sizeof(struct pollfd));
for (i = 0; i < socknum; i++) {
pfd[i].fd = socklist[i];
pfd[i].events = POLLIN;
}
+ pfd[socknum].fd = child_handler_pipe[0];
+ pfd[socknum].events = POLLIN;
signal(SIGCHLD, child_handler);
for (;;) {
int i;
- if (poll(pfd, socknum, -1) < 0) {
+ if (poll(pfd, socknum + 1, -1) < 0) {
if (errno != EINTR) {
error("poll failed, resuming: %s",
strerror(errno));
@@ -937,6 +960,10 @@ static int service_loop(int socknum, int *socklist)
}
continue;
}
+ if (pfd[socknum].revents & POLLIN) {
+ read(child_handler_pipe[0], &i, 1);
+ check_dead_children();
+ }
for (i = 0; i < socknum; i++) {
if (pfd[i].revents & POLLIN) {
--
1.5.6.1.300.gca3f
