On 05/05, Vegard Nossum wrote:
>
> If a kthread forks (e.g. usermodehelper since commit 1da5c46fa965) but
> fails in copy_process() between calling dup_task_struct() and setting
> p->set_child_tid, then the value of p->set_child_tid will be inherited
> from the parent and get prematurely freed by free_kthread_struct().
Aaah... thanks!
> --- a/kernel/fork.c
> +++ b/kernel/fork.c
> @@ -518,6 +518,13 @@ static struct task_struct *dup_task_struct(struct
> task_struct *orig, int node)
> atomic_set(&tsk->stack_refcount, 1);
> #endif
>
> + /*
> + * Forking kthreads (e.g. usermodehelper) should not inherit this
> + * field since it's a pointer to a 'struct kthread' which is not
> + * reference counted.
> + */
> + tsk->set_child_tid = NULL;
> +
Can't we just move both
p->set_child_tid = (clone_flags & CLONE_CHILD_SETTID) ? child_tidptr :
NULL;
/*
* Clear TID on mm_release()?
*/
p->clear_child_tid = (clone_flags & CLONE_CHILD_CLEARTID) ?
child_tidptr : NULL;
lines here?
Oleg.
