Re: [PATCH] remove BUG_ON(p->ptrace) in release_task()

From: OGAWA Hirofumi (hirofumi@mail.parknet.co.jp)
Date: Mon Sep 02 2002 - 08:33:16 EST

Daniel Jacobowitz <dan@debian.org> writes:

> On Mon, Sep 02, 2002 at 02:38:03AM +0900, OGAWA Hirofumi wrote:
> > Hi,
> >
> > I think, BUG_ON(p->ptrace) will be called if the CLONE_DETACH process
> > is traced. This patch removes BUG_ON(p->ptrace), and also removes
> > BUG_ON(p->ptrace) workaround in sys_wait4().
>
> The BUG_ON is correct, and that isn't a workaround - if the list is not
> empty, then it will be garbage after the task struct is freed. Your
> patch breaks tracing of normal processes again, because the ptrace_list
> will not be empty.

Whoops, yes, I'm wrong. Sorry. My fixes wasn't enough. However, looks
like your case called the following BUG().

sys_ptrace()
    -> ptrace_attach()
        -> __ptrace_link()

void __ptrace_link(task_t *child, task_t *new_parent)
{
        if (!list_empty(&child->ptrace_list))
                BUG();
        if (child->parent == new_parent)
                BUG(); <--- this
        list_add(&child->ptrace_list, &child->parent->ptrace_children);
        REMOVE_LINKS(child);

So, I need to look source more. Thanks. 

-- 
OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
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This archive was generated by hypermail 2b29 : Sat Sep 07 2002 - 22:00:15 EST