src/signal.c

/*
 * Asynchronous signal delivery functions.
 *
 * Copyright 2000-2010 Willy Tarreau <w@1wt.eu>
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version
 * 2 of the License, or (at your option) any later version.
 *
 */

#include <signal.h>
#include <string.h>

#include <haproxy/errors.h>
#include <haproxy/signal.h>
#include <haproxy/task.h>

/* Principle : we keep an in-order list of the first occurrence of all received
 * signals. All occurrences of a same signal are grouped though. The signal
 * queue does not need to be deeper than the number of signals we can handle.
 * The handlers will be called asynchronously with the signal number. They can
 * check themselves the number of calls by checking the descriptor this signal.
 */

int signal_queue_len; /* length of signal queue, <= MAX_SIGNAL (1 entry per signal max) */
int signal_queue[MAX_SIGNAL];                     /* in-order queue of received signals */
struct signal_descriptor signal_state[MAX_SIGNAL];
sigset_t blocked_sig;
int signal_pending = 0; /* non-zero if t least one signal remains unprocessed */

DECLARE_STATIC_POOL(pool_head_sig_handlers, "sig_handlers", sizeof(struct sig_handler));

/* Common signal handler, used by all signals. Received signals are queued.
 * Signal number zero has a specific status, as it cannot be delivered by the
 * system, any function may call it to perform asynchronous signal delivery.
 */
void signal_handler(int sig)
{
	if (sig < 0 || sig >= MAX_SIGNAL) {
		/* unhandled signal */
		signal(sig, SIG_IGN);
		qfprintf(stderr, "Received unhandled signal %d. Signal has been disabled.\n", sig);
		return;
	}

	if (!signal_state[sig].count) {
		/* signal was not queued yet */
		if (signal_queue_len < MAX_SIGNAL)
			signal_queue[signal_queue_len++] = sig;
		else
			qfprintf(stderr, "Signal %d : signal queue is unexpectedly full.\n", sig);
	}

	signal_state[sig].count++;
	if (sig)
		signal(sig, signal_handler); /* re-arm signal */

	/* If the thread is TH_FL_SLEEPING we need to wake it */
	wake_thread(tid);
}

/* Call handlers of all pending signals and clear counts and queue length. The
 * handlers may unregister themselves by calling signal_register() while they
 * are called, just like it is done with normal signal handlers.
 * Note that it is more efficient to call the inline version which checks the
 * queue length before getting here.
 */
void __signal_process_queue()
{
	int sig, cur_pos = 0;
	struct signal_descriptor *desc;
	sigset_t old_sig;

	/* block signal delivery during processing */
	ha_sigmask(SIG_SETMASK, &blocked_sig, &old_sig);

	/* It is important that we scan the queue forwards so that we can
	 * catch any signal that would have been queued by another signal
	 * handler. That allows real signal handlers to redistribute signals
	 * to tasks subscribed to signal zero.
	 */
	for (cur_pos = 0; cur_pos < signal_queue_len; cur_pos++) {
		sig  = signal_queue[cur_pos];
		desc = &signal_state[sig];
		if (desc->count) {
			struct sig_handler *sh, *shb;
			list_for_each_entry_safe(sh, shb, &desc->handlers, list) {
				if ((sh->flags & SIG_F_TYPE_FCT) && sh->handler)
					((void (*)(struct sig_handler *))sh->handler)(sh);
				else if ((sh->flags & SIG_F_TYPE_TASK) && sh->handler)
					task_wakeup(sh->handler, TASK_WOKEN_SIGNAL);
			}
			desc->count = 0;
		}
	}
	signal_queue_len = 0;

	/* restore signal delivery */
	ha_sigmask(SIG_SETMASK, &old_sig, NULL);
}

/* perform minimal intializations */
static void signal_init()
{
	int sig;

	signal_queue_len = 0;
	memset(signal_queue, 0, sizeof(signal_queue));
	memset(signal_state, 0, sizeof(signal_state));

	sigfillset(&blocked_sig);
	sigdelset(&blocked_sig, SIGPROF);
	/* man sigprocmask: If SIGBUS, SIGFPE, SIGILL, or SIGSEGV are
	   generated while they are blocked, the result is undefined, unless
	   the signal was generated by kill(2),
	   sigqueue(3), or raise(3).
	   Do not ignore WDTSIG or DEBUGSIG either, or it may deadlock the
	   watchdog */
	sigdelset(&blocked_sig, SIGBUS);
	sigdelset(&blocked_sig, SIGFPE);
	sigdelset(&blocked_sig, SIGILL);
	sigdelset(&blocked_sig, SIGSEGV);
#ifdef DEBUGSIG
	sigdelset(&blocked_sig, DEBUGSIG);
#endif
#ifdef WDTSIG
	sigdelset(&blocked_sig, WDTSIG);
#endif
	for (sig = 0; sig < MAX_SIGNAL; sig++)
		LIST_INIT(&signal_state[sig].handlers);
}

/*
 * This function should be called to unblock all signals
 */
void haproxy_unblock_signals()
{
	sigset_t set;

	/* Ensure signals are not blocked. Some shells or service managers may
	 * accidentally block all of our signals unfortunately, causing lots of
	 * zombie processes to remain in the background during reloads.
	 */
	sigemptyset(&set);
	ha_sigmask(SIG_SETMASK, &set, NULL);
}

/* releases all registered signal handlers */
void deinit_signals()
{
	int sig;
	struct sig_handler *sh, *shb;

	for (sig = 0; sig < MAX_SIGNAL; sig++) {
		if (sig != SIGPROF)
			signal(sig, SIG_DFL);
		list_for_each_entry_safe(sh, shb, &signal_state[sig].handlers, list) {
			LIST_DELETE(&sh->list);
			pool_free(pool_head_sig_handlers, sh);
		}
	}
}

/* Register a function and an integer argument on a signal. A pointer to the
 * newly allocated sig_handler is returned, or NULL in case of any error. The
 * caller is responsible for unregistering the function when not used anymore.
 * Note that passing a NULL as the function pointer enables interception of the
 * signal without processing, which is identical to SIG_IGN. If the signal is
 * zero (which the system cannot deliver), only internal functions will be able
 * to notify the registered functions.
 */
struct sig_handler *signal_register_fct(int sig, void (*fct)(struct sig_handler *), int arg)
{
	struct sig_handler *sh;

	if (sig < 0 || sig >= MAX_SIGNAL)
		return NULL;

	if (sig)
		signal(sig, fct ? signal_handler : SIG_IGN);

	if (!fct)
		return NULL;

	sh = pool_alloc(pool_head_sig_handlers);
	if (!sh)
		return NULL;

	sh->handler = fct;
	sh->arg = arg;
	sh->flags = SIG_F_TYPE_FCT;
	LIST_APPEND(&signal_state[sig].handlers, &sh->list);
	return sh;
}

/* Register a task and a wake-up reason on a signal. A pointer to the newly
 * allocated sig_handler is returned, or NULL in case of any error. The caller
 * is responsible for unregistering the task when not used anymore. Note that
 * passing a NULL as the task pointer enables interception of the signal
 * without processing, which is identical to SIG_IGN. If the signal is zero
 * (which the system cannot deliver), only internal functions will be able to
 * notify the registered functions.
 */
struct sig_handler *signal_register_task(int sig, struct task *task, int reason)
{
	struct sig_handler *sh;

	if (sig < 0 || sig >= MAX_SIGNAL)
		return NULL;

	if (sig)
		signal(sig, signal_handler);

	if (!task)
		return NULL;

	sh = pool_alloc(pool_head_sig_handlers);
	if (!sh)
		return NULL;

	sh->handler = task;
	sh->arg = reason & ~TASK_WOKEN_ANY;
	sh->flags = SIG_F_TYPE_TASK;
	LIST_APPEND(&signal_state[sig].handlers, &sh->list);
	return sh;
}

/* Immediately unregister a handler so that no further signals may be delivered
 * to it. The struct is released so the caller may not reference it anymore.
 */
void signal_unregister_handler(struct sig_handler *handler)
{
	LIST_DELETE(&handler->list);
	pool_free(pool_head_sig_handlers, handler);
}

/* Immediately unregister a handler so that no further signals may be delivered
 * to it. The handler struct does not need to be known, only the function or
 * task pointer. This method is expensive because it scans all the list, so it
 * should only be used for rare cases (eg: exit). The struct is released so the
 * caller may not reference it anymore.
 */
void signal_unregister_target(int sig, void *target)
{
	struct sig_handler *sh, *shb;

	if (sig < 0 || sig >= MAX_SIGNAL)
		return;

	if (!target)
		return;

	list_for_each_entry_safe(sh, shb, &signal_state[sig].handlers, list) {
		if (sh->handler == target) {
			LIST_DELETE(&sh->list);
			pool_free(pool_head_sig_handlers, sh);
			break;
		}
	}
}

/*
 * Immedialtely unregister every handler assigned to a signal <sig>.
 * Once the handler list is empty, the signal is ignored with SIG_IGN.
 */

void signal_unregister(int sig)
{
	struct sig_handler *sh, *shb;

	if (sig < 0 || sig >= MAX_SIGNAL)
		return;

	list_for_each_entry_safe(sh, shb, &signal_state[sig].handlers, list) {
		LIST_DELETE(&sh->list);
		pool_free(pool_head_sig_handlers, sh);
	}

	signal(sig, SIG_IGN);
}

INITCALL0(STG_PREPARE, signal_init);