Hi All,
I have been haunted by a problem with SMP kernels since 2.4.1. I have an
application program that causes dual processor kernels or Pentium MT
kernels to crash. I have tried to find the cause myself but have not been
succesful in that.
The (original) application does basically:
Open a serial port / write a few bytes / toggle RTS / read a few bytes /
close port.
It does it up to twice a second. There may however arrive bytes while
closing the port.
Attached is a program that demonstrates it. I tried it and yes, my
Linux version 2.4.31 (root@merin) (gcc version 3.3.5 (Debian 1:3.3.5-13)) #1
SMP Tue Oct 25 12:31:57 CEST 2005
crashed within 10 minutes :-((((((((
It locks up totally.
I found that 2.6 kernels will crash (at least with the original application)
too.
The serial input data is to be 'simulated' with a square wave generator on
the com port input.
You need a frequency generator of about 1300 Hertz to set the test up.
I have never been able to catch the underlying bug myself. It is probabely a
race problem somewhere in the interrupt allocation/de-allocation part..
I hope that someone with a spare SMP system (my SMP system is my
workstation at work, so I don't like the crashes at all) can try this and
catch the bug.
kind regards
Kees
#include <string.h>
#include <stdio.h>
#include <fcntl.h>
#include <stdlib.h>
#include <termio.h>
#include <unistd.h>
#include <sys/poll.h>
#include <signal.h>
/* this test program seeks to demonstrate a (longstanding) problem in
* 2.4 and 2.6 SMP kernels.
* The original application that is hindered by the problem is different
* but this demo program contains enough aspects that it will crash a
* SMP linux system soon. My experience is between almost direct to about 30 minutes.
*
* I have been able to immuminize only the 2.4.4 kernel. The same patch on later kernels did
* not help any longer.
*
* in order to test it apply a square wave generator to a serial port i.e.
* /dev/ttyS0, I tested with +/ 2.5 Volts and 1300 Hertz. This produces a '?' character
* if the port is read with
* (stty 1200 cs8 </dev/ttyS0 ; cat /dev/ttyS0)
*
* +----------------+
* | | signal -----------
* | 1.3 kHz |-------------------| 470 Ohm |----------------- pin 3 serial connector
* | | -----------
* | +/- 2.5 Volts |
* | square wave | ground
* | |----------------------------------------------- pin 7 serial connector
* +----------------+
*
*
* the test program can be run with
*
* crash_test -H /dev/ttyS0 (assuming that this is the correct port)
*
* the -S option disables the consequetive opening and closing of the port, if this option
* is applied, NO crash follows.
*
* kees schoenmakers [email protected] / [email protected]
*
*/
int test_open(), read_char();
void test_nrts(), test_close();
int smp_opt=0;
struct termio tio;
struct pollfd testfd;
unsigned char tbuf[32];
int main(argc, argv )
int argc;
char **argv;
{
char c;
int i;
char *portname="";
while (( c= getopt(argc, argv, "SH:")) != -1){
switch (c) {
case 'H':
portname=optarg;
break;
case 'S':
smp_opt++;
break;
exit(1);
}
}
testfd.fd = -1;
testfd.events= 0 |POLLIN;
sprintf((char *)&tbuf, "test\n");
signal( SIGFPE, SIG_IGN);
if( !strlen(portname)){
if((portname = getenv("TEST_PORT")) == NULL){
fprintf(stderr,"Port unknown, set TEST_PORT\n");
exit(1);
}
}
while(1){ /* main loop this does it !! */
if( test_open( portname) < 0)
exit(-2);
write(testfd.fd, (char *) &tbuf, strlen (tbuf));
test_nrts();
for( i =0 ; i < 6 ; i++){
read_char(testfd.fd);
}
test_close();
usleep(10000);
} /* 'main' while */
}
int test_open(portname)
char *portname;
{
extern int errno;
if( testfd.fd == -1){
if((testfd.fd = open(portname , O_RDWR)) < 0){
printf("*** can't open %s port, error %d \n",portname, errno);
testfd.fd = -1;
return (-1);
}
ioctl(testfd.fd , TCGETA, &tio);
tio.c_cflag = CS8 | B1200 | CREAD | CLOCAL;
tio.c_iflag = IGNBRK;
tio.c_lflag = 0;
tio.c_oflag = 0;
tio.c_cc[4] = 1;
tio.c_cc[5] = 1;
ioctl(testfd.fd , TCSETA, &tio);
}
return(0);
}
/* switch from xmit to receive, toggle RTS line */
void test_nrts()
{
int parm;
usleep(1000); /* wait for buffer to drain */
while(1){
ioctl(testfd.fd, TIOCSERGETLSR, &parm);
if (parm)
break;
}
ioctl(testfd.fd, TIOCMGET, &parm);
parm &= ~TIOCM_RTS; /* RTS off */
ioctl(testfd.fd, TIOCMSET, &parm );
return;
}
void test_close()
{
int parm;
if(!smp_opt){ /* normally close the port */
if( testfd.fd >=0)
close( testfd.fd);
testfd.fd = -1;
} else {
usleep(1000);
/* put RTS back on */
ioctl(testfd.fd, TIOCMGET, &parm);
parm |= TIOCM_RTS; /* RTS on */
ioctl(testfd.fd, TIOCMSET, &parm );
}
}
int read_char()
{
unsigned char c;
int r_stat;
r_stat=poll(&testfd, 1, 10);
if(r_stat > 0)
read(testfd.fd, &c, 1);
return (int) c;
}
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