Signal left blocked after signal handler.

[bruce@perens.com (Bruce Perens)]

Hi,

A signal should be blocked while its signal handler is executing, and
then unblocked when the handler returns - unless SA_NOMASK is set.

-test9 and -test10 leave the signal _blocked_forever_.

This causes the build-time confidence test for Electric Fence to break,
and no doubt lots of other code.

If SA_NOMASK is set, the signal is not blocked.

Test program attached below.

	Thanks

	Bruce

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <signal.h>
#include <setjmp.h>

static sigjmp_buf	sjbuf;
static int		sig = SIGINT;

static void
handler(int i)
{
	struct sigaction	act;

	memset((void *)&act, 0, sizeof(act));
	act.sa_handler = SIG_DFL;

	fprintf(stderr, "Signal handler hit!\n");
	fflush(stderr);
	sigaction(sig, &act, 0);
	siglongjmp(sjbuf, 1);

}

static void
invoke_signal()
{
	struct sigaction	act;

	memset((void *)&act, 0, sizeof(act));
	act.sa_handler = handler;

	/* act.sa_flags = SA_NOMASK; */

	if ( sigsetjmp(sjbuf, 0) == 0 ) {
		sigaction(sig, &act, 0);
		fprintf(stderr, "Sending signal... ");
		fflush(stderr);
		kill(getpid(), sig);
		fprintf(stderr, "Huh? Nothing happened. Signal was left blocked.\n");
	}
}

int
main(int argc, char * * argv)
{
	sigset_t	set;

	sigemptyset(&set);
	sigaddset(&set, sig);

	invoke_signal();
	invoke_signal();
	fprintf(stderr, "Unblocking signal... ");
	if ( sigsetjmp(sjbuf, 0) == 0 ) {
		sigprocmask(SIG_UNBLOCK,  &set, 0);
	}

	return 0;
}