Date: Wed, 11 Aug 1999 10:04:26 -0700 From: Jason Thorpe <thorpej@nas.nasa.gov> To: Oleg Derevenetz <oleg@oleg.sani-c.vrn.ru> Cc: freebsd-hackers@FreeBSD.ORG Subject: Re: mmap bug Message-ID: <199908111704.KAA26592@lestat.nas.nasa.gov>
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On Wed, 11 Aug 1999 20:48:08 +0400 (MSD)
Oleg Derevenetz <oleg@oleg.sani-c.vrn.ru> wrote:
> This small program, running as 'mmap', not 'mmap -u', can hang my machine.
> Is this a known bug in FreeBSD's kernel, or it is my fantasy ?
> Thank you for answer.
If it hangs your system, must be a bug in FreeBSD. Here is what happens
on a NetBSD/alpha system:
bishop:thorpej 26$ ./mmap-bug
unlink files? NO
mmaping 10485760 byte region on file 0
Memory fault (core dumped)
bishop:thorpej 27$ ./mmap-bug -u
unlink files? YES
mmaping 10485760 byte region on file 0
Memory fault (core dumped)
bishop:thorpej 28$
...which is correct. There isn't any backing store for the region
you've mapped.
>
> #include <stdio.h>
> #include <stdlib.h>
> #include <sys/types.h>
> #include <sys/mman.h>
> #include <unistd.h>
> #include <fcntl.h>
> #include <errno.h>
>
> main(int argc, char *argv[])
> {
> int fd;
> int i;
> int len=1024*1024*10; /*ie 10Mbytes*/
> caddr_t addr;
> char ttt[80];
> int bunlink = 0;
>
> if ( argc > 1 && strcmp(argv[1], "-u") == 0 ) {
> bunlink = 1;
> }
> printf("unlink files? %s\n", bunlink ? "YES" : "NO");
>
> for (i=0;;i++)
> {
> sprintf (ttt,"%d",i);
> printf("mmaping %ld byte region on file %s\n", len, ttt);
> fd=open(ttt,O_CREAT|O_RDWR,0666);
> if (fd<0)
> {
> printf("mmap error %ld",errno);
> exit(1);
> }
> memset(addr,'x',len);
> if ( munmap(addr, len) != 0 ) {
> fprintf(stderr, "munmap failed\n");
> exit(EXIT_FAILURE);
> }
> close(fd);
> if ( bunlink ) unlink(ttt);
> }
> }
>
>
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-- Jason R. Thorpe <thorpej@nas.nasa.gov>
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