Subject: Re: 2.6.23-mm1 thread exit_group issue

From: Andrew Morton <[email-masked]>
Date: Fri, 12 Oct 2007 18:03:49 -0700

On Fri, 12 Oct 2007 15:47:59 -0400
Mathieu Desnoyers <[email-masked]> wrote:

> Hi Andrew,
> 
> I noticed a regression between 2.6.23-rc8-mm2 and 2.6.23-mm1 (with your
> hotfixes). User space threads seems to receive a ERESTART_RESTARTBLOCK
> as soon as a thread does a pthread_join on them. The previous behavior
> was to wait for them to exit by taking a futex.
> 
> I provide a toy program that shows the problem. On 2.6.23-rc8-mm2, it
> loops forever (as it should). On 2.6.23-mm1, it exits after 10 seconds.
> 
> Any idea on what may cause this problem ?

Bisection shows that this problem is caused by these two patches:

pid-namespaces-allow-cloning-of-new-namespace.patch
pid-namespaces-allow-cloning-of-new-namespace-fix-check-for-return-value-of-create_pid_namespace.patch

> (I also provide complete ptrace -f of a correct and buggy run and my
> kernel config. Tests were done on i386.)
> 
> Mathieu
> 
> 
> /*
>  * Thread testing
>  *
>  * build with gcc -lpthread -o pthread pthread.c
>  *
>  * Mathieu Desnoyers
>  * License: GPL
>  */
> 
> #include <stdio.h>
> #include <pthread.h>
> #include <stdlib.h>
> #include <sys/types.h>
> #include <sys/wait.h>
> #include <unistd.h>
> #include <stdio.h>
> #include <signal.h>
> 
> static int __thread test = 0;
> 
> /* signal handler */
> void handler(int signo)
> {
> 	printf("Sig handler : TID %lu, pid : %lu\n", pthread_self(), getpid());
> }
> 
> void *thr1(void *arg)
> {
> 	test = 1;
> 	
> 	while(1) {
> 		printf("thread 1, thread id : %lu, pid %lu, test %d\n",
> 				pthread_self(), getpid(), test);
> 		sleep(2);
> 	}
> 	return ((void*)1);
> 
> }
> 
> void *thr2(void *arg)
> {
> 	while(1) { 
> 		printf("thread 2, thread id : %lu, pid %lu, test %d\n",
> 				pthread_self(), getpid(), test);
> 		sleep(2);
> 	}
> 	return ((void*)2);
> }
> 
> int main()
> {
> 	int err;
> 	pthread_t tid1, tid2;
> 	void *tret;
> 	static struct sigaction act;
> 
> 	act.sa_handler = handler;
> 	sigemptyset(&(act.sa_mask));
> 	sigaddset(&(act.sa_mask), SIGUSR1);
> 	sigaction(SIGUSR1, &act, NULL);
> 
> 	err = pthread_create(&tid1, NULL, thr1, NULL);
> 	if (err != 0)
> 		exit(1);
> 
> 	err = pthread_create(&tid2, NULL, thr2, NULL);
> 	if (err != 0)
> 		exit(1);
> 
> 	sleep(10);
> 
> 	err = pthread_join(tid1, &tret);
> 	if (err != 0)
> 		exit(1);
> 
> 	err = pthread_join(tid2, &tret);
> 	if (err != 0)
> 		exit(1);
> 
> 	return 0;
> }
>