1#!/bin/sh 2 3# 4# Copyright (c) 2009 Peter Holm <pho@FreeBSD.org> 5# All rights reserved. 6# 7# Redistribution and use in source and binary forms, with or without 8# modification, are permitted provided that the following conditions 9# are met: 10# 1. Redistributions of source code must retain the above copyright 11# notice, this list of conditions and the following disclaimer. 12# 2. Redistributions in binary form must reproduce the above copyright 13# notice, this list of conditions and the following disclaimer in the 14# documentation and/or other materials provided with the distribution. 15# 16# THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND 17# ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 18# IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 19# ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE 20# FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 21# DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 22# OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 23# HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 24# LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 25# OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 26# SUCH DAMAGE. 27# 28# $FreeBSD$ 29# 30 31# There is a well-known problem in FreeBSD, caused by allowing page faults 32# while doing filesystem data move to or from userspace during read(2) and 33# write(2). The issue is that if the userspace address being read or write 34# from/to is backed by the mapping of the same file we are doing i/o to, 35# we deadlock. 36 37# Test scenario by ups 38 39[ `id -u ` -ne 0 ] && echo "Must be root!" && exit 1 40 41here=`pwd` 42cd /tmp 43sed '1,/^EOF/d' < $here/$0 > dl.c 44cc -o dl -Wall dl.c 45rm -f dl.c 46 47n=5 48old=`sysctl vm.old_msync | awk '{print $NF}'` 49sysctl vm.old_msync=1 50for i in `jot $n`; do 51 mkdir -p /tmp/dl.dir.$i 52 cd /tmp/dl.dir.$i 53 /tmp/dl & 54done 55cd /tmp 56for i in `jot $n`; do 57 wait 58done 59for i in `jot $n`; do 60 rm -rf /tmp/dl.dir.$i 61done 62sysctl vm.old_msync=$old 63 64rm -rf /tmp/dl 65exit 0 66EOF 67#include <sys/types.h> 68#include <unistd.h> 69#include <sys/stat.h> 70#include <fcntl.h> 71#include <stdio.h> 72#include <stdlib.h> 73#include <sys/mman.h> 74 75 76int prepareFile(char* filename,int* fdp); 77int mapBuffer(char** bufferp,int fd1,int fd2); 78int startIO(int fd,char *buffer); 79 80int pagesize; 81 82#define FILESIZE (32*1024) 83char wbuffer[FILESIZE]; 84 85/* Create a FILESIZE sized file - then remove file data from the cache*/ 86int prepareFile(char* filename,int* fdp) 87{ 88 int fd; 89 int len; 90 int status; 91 void *addr; 92 93 fd = open(filename,O_CREAT | O_TRUNC | O_RDWR,S_IRWXU); 94 if (fd == -1) 95 { 96 perror("Creating file"); 97 return fd; 98 } 99 100 len = write(fd,wbuffer,FILESIZE); 101 if (len < 0) 102 { 103 perror("Write failed"); 104 return 1; 105 } 106 107 status = fsync(fd); 108 if (status != 0) 109 { 110 perror("fsync failed"); 111 return 1; 112 } 113 114 addr = mmap(NULL,FILESIZE, PROT_READ | PROT_WRITE , MAP_SHARED, fd, 0); 115 if (addr == MAP_FAILED) 116 { 117 perror("Mmap failed"); 118 return 1; 119 } 120 121 status = msync(addr,FILESIZE,MS_INVALIDATE | MS_SYNC); 122 if (status != 0) 123 { 124 perror("Msync failed"); 125 return 1; 126 } 127 128 munmap(addr,FILESIZE); 129 130 *fdp = fd; 131 return 0; 132} 133 134 135/* mmap a 2 page buffer - first page is from fd1, second page from fd2 */ 136int mapBuffer(char** bufferp,int fd1,int fd2) 137{ 138 void* addr; 139 char *buffer; 140 141 addr = mmap(NULL,pagesize*2, PROT_READ | PROT_WRITE , MAP_SHARED, fd1, 0); 142 if (addr == MAP_FAILED) 143 { 144 perror("Mmap failed"); 145 return 1; 146 } 147 148 buffer = addr; 149 addr = mmap(buffer + pagesize,pagesize, PROT_READ | PROT_WRITE , MAP_FIXED | 150MAP_SHARED, fd2, 0); 151 152 if (addr == MAP_FAILED) 153 { 154 perror("Mmap2 failed"); 155 return 1; 156 } 157 *bufferp = buffer; 158 return 0; 159} 160 161 162int startIO(int fd,char *buffer) 163{ 164 ssize_t len; 165 len = write(fd,buffer,2*pagesize); 166 if (len == -1) 167 { 168 perror("write failed"); 169 return 1; 170 } 171 return 0; 172} 173 174 175int main(int argc,char *argv[],char *envp[]) 176{ 177 178 int fdA,fdB,fdDelayA,fdDelayB; 179 int status; 180 char *bufferA,*bufferB; 181 pid_t pid; 182 183 pagesize = getpagesize(); 184 185 if ((prepareFile("A",&fdA)) 186 || (prepareFile("B",&fdB)) 187 || (prepareFile("DelayA",&fdDelayA)) 188 || (prepareFile("DelayB",&fdDelayB)) 189 || (mapBuffer(&bufferA,fdDelayA,fdB)) 190 || (mapBuffer(&bufferB,fdDelayB,fdA))) 191 exit(1); 192 193 pid = fork(); 194 195 if (pid == 0) 196 { 197 status = startIO(fdA,bufferA); 198 exit(status); 199 } 200 201 if (pid == -1) 202 { 203 exit(1); 204 } 205 status = startIO(fdB,bufferB); 206 exit(status); 207 208} 209