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Date: Thu, 23 Jun 2016 19:03:52 +0200
From: Oleg Nesterov <>
To: Linus Torvalds <>
Cc: Andy Lutomirski <>, Andy Lutomirski <>,
        the arch/x86 maintainers <>,
        Linux Kernel Mailing List <>,
        "" <>,
        Borislav Petkov <>, Nadav Amit <>,
        Kees Cook <>, Brian Gerst <>,
        "" <>,
        Josh Poimboeuf <>, Jann Horn <>,
        Heiko Carstens <>
Subject: Re: [PATCH v3 00/13] Virtually mapped stacks with guard pages (x86,

On 06/23, Linus Torvalds wrote:
> But that does bring up another possibility: do it at wait() time, when
> we do release_thread(). That's when we *used* to synchronously free
> it, before we did the lockless RCU walks.

Let me quote my previous email ;)

	And we can't free/nullify it when the parent/debuger reaps a zombie,
	say, mark_oom_victim() expects that get_task_struct() protects
	thread_info as well.

probably we can fix all such users though...

> At that point, it has been removed from all the thread lists. So the
> only way to find it is through the RCU walks. Do any of *those* touch
> ti->flags? I'm not seeing it,

Neither me, although I didn't try to grep too much.

> and it sounds fixable if any do

probably yes, but this would mean that tasklist_lock protects task->stack,
doesn't look really nice...


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