Unkillable gdb process gets system unusably slow

[Timo Sirainen <tss@iki.fi>]

Fully reproducible with me. v2.6.23.1 x86-64 SMP kernel, Core 2 CPU, gdb
v6.6.90.20070912-debian.

gdb ./hang
run
fr 1
p (char*)base

p command hangs and the entire system becomes unusably slow. kill -9
doesn't kill gdb.

/* gcc hang.c -o hang -g -Wall */
#include <stdio.h>
#include <string.h>
#include <fcntl.h>
#include <unistd.h>
#include <sys/mman.h>

int main(void)
{
	int fd;
	char buf[100];
	void *base;

	fd = open("hang.tmp", O_RDWR | O_CREAT, 0600);
	if (fd == -1) perror("open");

	base = mmap(NULL, 100, PROT_READ|PROT_WRITE, MAP_SHARED, fd, 0);
	if (base == MAP_FAILED)
		perror("mmap");
	memcpy(buf, base, sizeof(buf));
	return 0;
}

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