Date: Sun, 30 May 1999 17:40:39 -0500 (CDT) From: toasty@dragondata.com To: FreeBSD-gnats-submit@freebsd.org Subject: kern/11948: mmaping memory device, then forking causes negative rss Message-ID: <199905302240.RAA83486@nfs.dragondata.com>
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>Number: 11948
>Category: kern
>Synopsis: mmaping memory device, then forking causes negative rss
>Confidential: no
>Severity: serious
>Priority: medium
>Responsible: freebsd-bugs
>State: open
>Quarter:
>Keywords:
>Date-Required:
>Class: sw-bug
>Submitter-Id: current-users
>Arrival-Date: Sun May 30 15:50:01 PDT 1999
>Closed-Date:
>Last-Modified:
>Originator: Kevin Day
>Release: FreeBSD 4.0-CURRENT i386
>Organization:
DragonData Internet Services, Inc.
>Environment:
3.1 or 4.0 system, with some mmapable device (/dev/mem or similar)
>Description:
When mmap'ing a device, then forking, the resident size of the child process
becomes negative.
>How-To-Repeat:
1.c:
#include <stdio.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/errno.h>
#include <sys/types.h>
#include <sys/mman.h>
void main(void) {
int k;
char *low;
int devmem;
devmem = open("/dev/mem",O_RDWR);
low1mb = (char *)mmap(0, 0x800000, (PROT_READ | PROT_WRITE), MAP_INHERIT | MAP_SHARED, devmem, 0);
printf("Starting 2...\n");
if (rfork(RFCFDG|RFPROC)) {
usleep(100);
} else {
k = execl("./2", "2", (char *) 0);
if (k) {
printf("io returned %d errno %d\n",k, errno);
}
_exit(0);
}
}
2.c:
void main(void) {
while(1)
sleep(10000);
}
Compile, and run '1'.
top shows:
PID USERNAME PRI NICE SIZE RES STATE TIME WCPU CPU COMMAND
899 root 10 0 748K 32760M nanslp 0:00 0.00% 0.00% 2
ps shows:
root 899 0.0 53622.9 748 -7960 p1 I 6:14AM 0:00.00 2
0 899 1 0 10 0 748 -7960 nanslp I p1 0:00.00 2
Repeatedly doing this will cause the kernel to panic with "panic: multiple
frees".
>Fix:
I couldn't find a fix for this within an hour of looking, and had to move
on. This appeared between 3.0 and 3.1, so it shouldn't be *too* hard to
find. :)
Kevin
>Release-Note:
>Audit-Trail:
>Unformatted:
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