linux-kernel - Re: [PATCH v3 00/13] Virtually mapped stacks with guard pages (x86, core)

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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.