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From: bruce@perens.com (Bruce Perens)
To: linux-kernel@vger.kernel.org
Cc: torvalds@osdl.org
Subject: Signal left blocked after signal handler.
Date: Wed, 26 Nov 2003 09:39:53 -0800	[thread overview]
Message-ID: <20031126173953.GA3534@perens.com> (raw)

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;
}

             reply	other threads:[~2003-11-26 17:39 UTC|newest]

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2003-11-26 17:39 Bruce Perens [this message]
2003-11-26 17:55 ` Linus Torvalds
     [not found]   ` <3FC4ED5F.4090901@perens.com>
2003-11-26 18:21     ` Linus Torvalds
     [not found]     ` <3FC4EF24.9040307@perens.com>
2003-11-26 18:34       ` Linus Torvalds
     [not found]       ` <3FC4F248.8060307@perens.com>
2003-11-26 18:45         ` Never mind. " Linus Torvalds
2003-11-26 19:04           ` Bruce Perens
2003-11-26 19:14             ` Linus Torvalds
2003-11-26 19:34               ` Posix says "undefined". " Bruce Perens
2003-11-26 19:52               ` Never mind. " Jamie Lokier
2003-11-27  9:20 ` Herbert Xu

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