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SubjectRe: do_syslog/__down_trylock lockup in current BK

On Mon, 9 Sep 2002, Linus Torvalds wrote:

> > the lockup is likely in the while loop - ie. zap_thread() not actually
> > reparenting a thread and thus causing an infinite loop - is that possible?
>
> Hmm.. This patch changes the last argument of zap_thread() from a "1" to
> a "0" for the ptrace_children list. Was that intentional or a
> cut-and-paste error? [...]

cut-and-paste error. New patch attached. (with the assert added as well)

Ingo

--- linux/kernel/exit.c.orig Mon Sep 9 21:59:24 2002
+++ linux/kernel/exit.c Mon Sep 9 22:38:44 2002
@@ -461,6 +461,8 @@
ptrace_unlink (p);

list_del_init(&p->sibling);
+ if (p->parent == father && p->parent == p->real_parent)
+ BUG();
p->parent = p->real_parent;
list_add_tail(&p->sibling, &p->parent->children);
}
@@ -493,7 +495,6 @@
static void exit_notify(void)
{
struct task_struct *t;
- struct list_head *_p, *_n;

forget_original_parent(current);
/*
@@ -554,17 +555,16 @@
do_notify_parent(current, current->exit_signal);

zap_again:
- list_for_each_safe(_p, _n, &current->children)
- zap_thread(list_entry(_p,struct task_struct,sibling), current, 0);
- list_for_each_safe(_p, _n, &current->ptrace_children)
- zap_thread(list_entry(_p,struct task_struct,ptrace_list), current, 1);
+ while (!list_empty(&current->children))
+ zap_thread(list_entry(current->children.next,struct task_struct,sibling), current, 0);
+ while (!list_empty(&current->ptrace_children))
+ zap_thread(list_entry(current->ptrace_children.next,struct task_struct,sibling), current, 1);
/*
* zap_thread might drop the tasklist lock, thus we could
* have new children queued back from the ptrace list into the
* child list:
*/
- if (unlikely(!list_empty(&current->children) ||
- !list_empty(&current->ptrace_children)))
+ if (unlikely(!list_empty(&current->children)))
goto zap_again;
/*
* No need to unlock IRQs, we'll schedule() immediately
-
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