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Message-ID: <20160623170352.GA17372@redhat.com>
Date: Thu, 23 Jun 2016 19:03:52 +0200
From: Oleg Nesterov <oleg@...hat.com>
To: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Andy Lutomirski <luto@...capital.net>, Andy Lutomirski <luto@...nel.org>,
the arch/x86 maintainers <x86@...nel.org>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
"linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
Borislav Petkov <bp@...en8.de>, Nadav Amit <nadav.amit@...il.com>,
Kees Cook <keescook@...omium.org>, Brian Gerst <brgerst@...il.com>,
"kernel-hardening@...ts.openwall.com" <kernel-hardening@...ts.openwall.com>,
Josh Poimboeuf <jpoimboe@...hat.com>, Jann Horn <jann@...jh.net>,
Heiko Carstens <heiko.carstens@...ibm.com>
Subject: Re: [PATCH v3 00/13] Virtually mapped stacks with guard pages (x86,
core)
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...
Oleg.
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