From owner-freebsd-stable  Thu Mar  4  2:49:10 1999
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Date: Thu, 4 Mar 1999 11:48:47 +0100
From: Marc Olzheim <marcolz@stack.nl>
To: freebsd-stable@FreeBSD.ORG
Subject: DOS with ktrace
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Hi.

When ktracing the following prog, FreeBSD 2.2.8 sometimes produces a deadlock
situation.

#include	<stdio.h>
#include	<unistd.h>
#include	<stdlib.h>
#include	<errno.h>
#include	<ctype.h>
#include	<fcntl.h>

extern	int
main (int argc, char **argv)
{
	char		buffer[1000000];
	int		result;

	if (fcntl(1, F_SETFL, O_NONBLOCK))
		err(1, "fcntl(1, F_SETFL, O_NONBLOCK)");
	bzero(buffer, sizeof(buffer));
	strcpy(buffer, "hoihoihoihoihoi!");
	for (;;)
	{
		result = write(1, buffer, sizeof(buffer));
		if (result == -1)
			warn("write(1, buffer, %d)", sizeof(buffer));
		else if (result == 0)
			errx(1, "result == 0");
		else if (result != sizeof(buffer))
			errx(1, "result == %d", result);
	}
	argc = 0; argv = NULL;
	return 0;
}

Just compile it and run it as:

ktrace -t cnsw ./testwrite > /tmp/foo

Then suspend it with ^Z

Any process trying to do filesystem-io will wait in locks. On a busy machine
it will soon run out of resources.

This does not happen 100% of the time, but it's very well reproducable, just
try one or two times.

I have no FreeBSD 3 boxes here yet to test it on, so I don't know wether it's
affected or not, but it does affect 2.2.6 (i.e. non-CAM).

Marc


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