Hi,
I found the problem, it was a bug in my own code. For details see below:
On Wed, Aug 12, 2015 at 05:09:31PM +0200, Phil Sutter wrote:
[...]
> Here is the reproducer code (kthread_test.c) I used:
>
> -----------------------------------8<-----------------------------------
> #include <linux/kthread.h>
> #include <linux/module.h>
> #include <linux/semaphore.h>
> #include <linux/slab.h>
>
> static int tcount = 100;
> module_param(tcount, int, 0);
> MODULE_PARM_DESC(tcount, "Number of threads to spawn (default: 100)");
>
> static struct semaphore prestart_sem;
> static struct semaphore startup_sem = __SEMAPHORE_INITIALIZER(startup_sem, 0);
>
> static int threadfunc(void *unused)
> {
> up(&prestart_sem);
> if (down_interruptible(&startup_sem))
> pr_warn("thread: down_interruptible failed!\n");
> printk(KERN_INFO "thread: running\n");
> return 0;
> }
This function exits without waiting for kthread_should_stop() to return
true, which allows for do_fork() to do the cleanup (inside
wait_for_vfork_done()).
> static int __init init_kthread_test(void)
> {
> struct task_struct **tsk;
> int i, err;
>
> tsk = kzalloc(tcount * sizeof(struct task_struct *), GFP_KERNEL);
> sema_init(&prestart_sem, 1 - tcount);
>
> printk(KERN_INFO "%s: starting test run\n", __func__);
>
> for (i = 0; i < tcount; i++) {
> tsk[i] = kthread_run(threadfunc, NULL, "thread[%d]", i);
> if (IS_ERR(tsk[i]))
> pr_warn("%s: kthread_run failed for thread %d\n",
> __func__, i);
> else
> printk(KERN_INFO "%s: started thread at %p\n",
> __func__, tsk[i]);
> }
>
> if (down_interruptible(&prestart_sem))
> pr_warn("%s: down_interruptible failed!\n", __func__);
> for (i = 0; i < tcount; i++)
> up(&startup_sem);
>
> for (i = 0; i < tcount; i++) {
> if (IS_ERR(tsk[i]))
> continue;
> if ((err = kthread_stop(tsk[i])))
> pr_warn("%s: kthread_stop failed for thread %d: %d\n",
> __func__, i, err);
Calling kthread_stop() for a thread that has already returned by itself
then leads to the problem of calling exit_creds() twice.
I wonder a bit if this should be covered for or not, as the call to
__put_task_struct is protected by a usage counter in struct task_struct.
I fixed the issue by looping over schedule() at the end of threadfunc()
until kthread_should_stop() returns true.
Cheers, Phil
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
