#!/bin/sh

#
# Copyright (c) 2009 Peter Holm <pho@FreeBSD.org>
# All rights reserved.
#
# Redistribution and use in source and binary forms, with or without
# modification, are permitted provided that the following conditions
# are met:
# 1. Redistributions of source code must retain the above copyright
#    notice, this list of conditions and the following disclaimer.
# 2. Redistributions in binary form must reproduce the above copyright
#    notice, this list of conditions and the following disclaimer in the
#    documentation and/or other materials provided with the distribution.
#
# THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
# ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
# IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
# ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
# FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
# DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
# OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
# HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
# LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
# OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
# SUCH DAMAGE.
#
# $FreeBSD$
#

# There is a well-known problem in FreeBSD, caused by allowing page faults
# while doing filesystem data move to or from userspace during read(2) and
# write(2). The issue is that if the userspace address being read or write
# from/to is backed by the mapping of the same file we are doing i/o to,
# we deadlock.

# Test scenario by ups

[ `id -u ` -ne 0 ] && echo "Must be root!" && exit 1

here=`pwd`
cd /tmp
sed '1,/^EOF/d' < $here/$0 > dl.c
cc -o dl -Wall dl.c
rm -f dl.c

n=5
old=`sysctl vm.old_msync | awk '{print $NF}'`
sysctl vm.old_msync=1
for i in `jot $n`; do
	mkdir -p /tmp/dl.dir.$i
	cd /tmp/dl.dir.$i
	/tmp/dl &
done
cd /tmp
for i in `jot $n`; do
	wait
done
for i in `jot $n`; do
	rm -rf /tmp/dl.dir.$i
done
sysctl vm.old_msync=$old

rm -rf /tmp/dl
exit 0
EOF
#include <sys/types.h>
#include <unistd.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/mman.h>


int prepareFile(char* filename,int* fdp);
int mapBuffer(char** bufferp,int fd1,int fd2);
int startIO(int fd,char *buffer);

int pagesize;

#define FILESIZE (32*1024)
char wbuffer[FILESIZE];

/* Create a FILESIZE sized file - then remove file data from the cache*/
int prepareFile(char* filename,int* fdp)
{
  int fd;
  int len;
  int status;
  void *addr;

  fd = open(filename,O_CREAT | O_TRUNC | O_RDWR,S_IRWXU);
  if (fd == -1)
    {
      perror("Creating file");
      return fd;
    }

  len = write(fd,wbuffer,FILESIZE);
  if (len < 0)
    {
      perror("Write failed");
      return 1;
    }

  status = fsync(fd);
   if (status != 0)
    {
        perror("fsync failed");
	return 1;
    }

  addr = mmap(NULL,FILESIZE, PROT_READ | PROT_WRITE , MAP_SHARED, fd, 0);
  if (addr == MAP_FAILED)
    {
      perror("Mmap failed");
      return 1;
    }

  status = msync(addr,FILESIZE,MS_INVALIDATE | MS_SYNC);
  if (status != 0)
    {
        perror("Msync failed");
	return 1;
    }

  munmap(addr,FILESIZE);

  *fdp = fd;
  return 0;
}


/* mmap a 2 page buffer - first page is from fd1, second page from fd2 */
int mapBuffer(char** bufferp,int fd1,int fd2)
{
  void* addr;
  char *buffer;

  addr = mmap(NULL,pagesize*2, PROT_READ | PROT_WRITE , MAP_SHARED, fd1, 0);
  if (addr == MAP_FAILED)
    {
      perror("Mmap failed");
      return 1;
    }

  buffer = addr;
  addr = mmap(buffer + pagesize,pagesize, PROT_READ | PROT_WRITE , MAP_FIXED |
MAP_SHARED, fd2, 0);

  if (addr == MAP_FAILED)
    {
      perror("Mmap2 failed");
      return 1;
    }
  *bufferp = buffer;
  return 0;
}


int startIO(int fd,char *buffer)
{
  ssize_t len;
  len = write(fd,buffer,2*pagesize);
  if (len == -1)
    {
      perror("write failed");
      return 1;
    }
  return 0;
}


int main(int argc,char *argv[],char *envp[])
{

  int fdA,fdB,fdDelayA,fdDelayB;
  int status;
  char *bufferA,*bufferB;
  pid_t pid;

  pagesize = getpagesize();

  if ((prepareFile("A",&fdA))
      || (prepareFile("B",&fdB))
      || (prepareFile("DelayA",&fdDelayA))
      || (prepareFile("DelayB",&fdDelayB))
      || (mapBuffer(&bufferA,fdDelayA,fdB))
      || (mapBuffer(&bufferB,fdDelayB,fdA)))
    exit(1);

  pid = fork();

  if (pid == 0)
    {
      status = startIO(fdA,bufferA);
      exit(status);
    }

  if (pid == -1)
    {
      exit(1);
    }
  status = startIO(fdB,bufferB);
  exit(status);

}
