On Fri, 20 Oct 2006 22:41:22 +0100, Ralf Baechle <[EMAIL PROTECTED]> wrote:
> > It's just that we weren't quite careful enough at that time (and even
> > then, that would only matter for some really really unlikely and strange
> > situations that only happen when you fork() from a _threaded_ environment,
> > so it shouldn't be anything you'd notice under normal load).
> >
> > I think.
>
> The flush is there since a very long time. I have it in my tree since
> ~ 2.1.36 and I get the feeling anybody every has been seriously revisited
> the issue since.
I think calling fork() (or system() or popen() or so) in threaded
program is neither very unlikely or strange. But this breakage happens
very rarely indeed, especially non-preemptive kernel.
During debugging this issue, I had used this test program and slightly
modified kernel --- inserting yield() at middle of dup_mmap().
With the modified kernel on 32KB VIPT D$, running this test program
some times could reproduce the breakage ("BAD!" messages). I heard
PARISC people had successed to reproduce it too.
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <pthread.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/wait.h>
static void *thread_func(void *arg)
{
unsigned char buf[2048], j;
int i;
for (j = 0; ; j++) {
/* fill buf[] with j */
memset(buf, j, sizeof(buf)/2);
sched_yield();
memset(buf + sizeof(buf)/2, j, sizeof(buf)/2);
sched_yield();
/* check buf[] contents */
for (i = 0; i < sizeof(buf); i++) {
if (buf[i] != j) {
printf("BAD! %p (%d != %d)\n",
buf + i, buf[i], j);
exit(1);
}
}
}
}
int main(int argc, char *argv[])
{
int i;
pid_t pid;
pthread_t tid;
for (i = 0; i < 4; i++)
pthread_create(&tid, NULL, thread_func, NULL);
for (i = 0; i < 100; i++) {
pid = fork();
if (pid == -1) {
perror("fork");
exit(1);
}
if (pid)
waitpid(pid, NULL, 0);
else
exit(0);
}
return 0;
}
---
Atsushi Nemoto
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