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Message-ID: <20160623181215.GA17813@redhat.com>
Date: Thu, 23 Jun 2016 20:12:16 +0200
From: Oleg Nesterov <oleg@...hat.com>
To: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Peter Zijlstra <peterz@...radead.org>,
        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:
>
> Ugh. Looking around at this, it turns out that a great example of this
> kind of legacy issue is the debug_mutex stuff.

Heh ;) I am looking at it too.

> It uses "struct thread_info *" as the owner pointer, and there is _no_
> existing reason for it. In fact, in every single place it actually
> wants the task_struct, and it does task_thread_info(task) just to
> convert it to the thread-info, and then converts it back with
> "ti->task".

Even worse, this task is always "current" afaics, so

> So the attached patch seems to be the right thing to do regardless of
> this whole discussion.

I think we should simply remove this argument.

And probably kill task_struct->blocked_on? I do not see the point of
this task->blocked_on != waiter check.

Oleg.

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