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Date: Tue, 22 Jun 2004 21:51:00 -0000
From: Thorsten Kukuk <kukuk@suse.de>
To: libc-hacker@sources.redhat.com
Subject: deadlock in signal handler with NPTL
Message-ID: <20040622215059.GA1204@suse.de>
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Organization: SuSE Linux AG, Nuernberg, Germany
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Hi,

I got the following test program. I know, it is very ugly and there
are a lot of things somebody should not do, but this is something
what programs like sshd are doing.

The problem is: This program deadlocks very fast in a FUTEX_WAIT
call. This does not happen with LinuxThreads.

Any ideas what goes wrong?

  Thorsten

-- 
Thorsten Kukuk       http://www.suse.de/~kukuk/        kukuk@suse.de
SuSE Linux AG        Maxfeldstr. 5                 D-90409 Nuernberg
--------------------------------------------------------------------    
Key fingerprint = A368 676B 5E1B 3E46 CFCE  2D97 F8FD 4E23 56C6 FB4B

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#include <sys/types.h>

#include <unistd.h>
#include <stdio.h>
#include <syslog.h>
#include <signal.h>


void
handler(int sig)
{
	syslog(LOG_DEBUG, "sigtest");
	printf("in handler\n");
	fflush(stdout);
}

int
main(int argc, char *argv[])
{
	pid_t pid;

	switch (pid = fork()) {
	case 0:
		break;
	case -1:
		perror("form");
		exit(1);
	default:
		signaller(pid);
		exit(0);
	}
	signal(SIGCHLD, handler);
	while (1) {
		syslog(LOG_DEBUG, "test");
		printf("in loop\n");
		fflush(stdout);
	}
}

int
signaller(pid_t pid)
{
	while (1) {
		usleep(1);
		kill(pid, SIGCHLD);
	}
}

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