linux-kernel - Re: [PATCH 0/5 v2] [GIT PULL] x86/jump label: Paranoid checks and 2 or 5 byte nops

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Date:	Sun, 5 Feb 2012 12:47:51 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	"H. Peter Anvin" <hpa@...or.com>, linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jason Baron <jbaron@...hat.com>,
	Frederic Weisbecker <fweisbec@...il.com>
Subject: Re: [PATCH 0/5 v2] [GIT PULL] x86/jump label: Paranoid checks and 2
 or 5 byte nops


* Steven Rostedt <rostedt@...dmis.org> wrote:

> On Fri, 2012-02-03 at 08:36 +0100, Ingo Molnar wrote:
> > * Steven Rostedt <rostedt@...dmis.org> wrote:
> > 
> > > Now I'm running a ktest bisect on the out-of-tree branch to 
> > > find the commit that prevents this box from booting. [...]
> > 
> > Let me know once you have found that and are able to boot -tip 
> > with your new bits applied. tip:out-of-tree needs definitely 
> > needs a cleanup - I'll probably even make it internal to my 
> > testing to not uglify tip:master.
> 
> Found it. I found this once before, but couldn't find it when I looked,
> but it was still there :-/
> 
> Anyway, here's the commit that prevents my box from booting:
> 
> commit 41e95d95208c62d4b0fbcee5f16d93e23ca32984
> Author: Ingo Molnar <mingo@...e.hu>
> Date:   Thu Sep 17 23:12:20 2009 +0200
> 
>     <not-for-merge> Disable DEVTMPFS_MOUNT for now
> 
> 
> It seems that this box requires DEVTMPFS_MOUNT to be set in 
> order to boot.

Hm, silly userspace, because the *enabling* of this option can 
break existing setups as well:

| Subject: [PATCH] <not-for-merge> Disable DEVTMPFS_MOUNT for now
|
| Causing bootup problems - /dev/zero and /dev/null not being there, etc.
|
| NOT-Signed-off-by: Ingo Molnar <mingo@...e.hu>

You could probably work it around by doing something like:

   mkdir /mnt2
   mount /dev/root /mnt2
   cp -a /dev/* /mnt2/

this will create the device nodes in /dev and make them 
available to early userspace even if it could not mount devtmpfs 
like it used to.

Thanks,

	Ingo
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