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

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Message-ID: <CA+55aFxzdFxUUCSDgt_5cPdL1NxS9GDtHOkPkwOui6PTuqEj+g@mail.gmail.com>
Date:	Tue, 28 Jun 2016 14:14:33 -0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Andy Lutomirski <luto@...capital.net>
Cc:	Oleg Nesterov <oleg@...hat.com>, Andy Lutomirski <luto@...nel.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 Tue, Jun 28, 2016 at 1:54 PM, Andy Lutomirski <luto@...capital.net> wrote:
>
> But I might need to that anyway for procfs to read the the stack,
> right?  Do you see another way to handle that case?

I think the other way to handle the kernel stack reading would be to
simply make the stack freeing be RCU-delayed, and use the RCU list
itself as the stack cache.

That way reading the stack is ok in a RCU context, although you might
end up reading a stack that has been re-used.

Would that work for people?

                Linus