linux-kernel - Re: kthread_stop insanity (Re: [[DEBUG] force] 2642458962: BUG: unable to handle kernel paging request at ffffc90000997f18)

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Date:	Wed, 29 Jun 2016 00:59:29 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Andy Lutomirski <luto@...capital.net>
Cc:	Andy Lutomirski <luto@...nel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Tejun Heo <tj@...nel.org>, LKP <lkp@...org>,
	LKML <linux-kernel@...r.kernel.org>,
	kernel test robot <xiaolong.ye@...el.com>
Subject: Re: kthread_stop insanity (Re: [[DEBUG] force] 2642458962: BUG:
 unable to handle kernel paging request at ffffc90000997f18)

On 06/28, Andy Lutomirski wrote:
>
> On Tue, Jun 28, 2016 at 1:12 PM, Oleg Nesterov <oleg@...hat.com> wrote:
> >
> > So please forget unless you see another reason for this change.
> >
>
> But I might need to that anyway for procfs to read the the stack,
> right?  Do you see another way to handle that case?

Well, we could use probe_kernel_text() and recheck tsk->stack != NULL
after this.

But,

> I'm thinking of adding:
>
> void *try_get_task_stack(struct task_struct *tsk);
> void put_task_stack(struct task_struct *tsk);

Yes, agreed, this looks better.

Oleg.