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From: David Miller <davem@davemloft.net>
To: tglx@linutronix.de
Cc: mikpe@it.uu.se, sparclinux@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [BUG] 2.6.25-rc3 hangs in early boot on Sun Ultra5
Date: Wed, 27 Feb 2008 11:05:38 -0800 (PST)	[thread overview]
Message-ID: <20080227.110538.160750982.davem@davemloft.net> (raw)
In-Reply-To: <alpine.LFD.1.00.0802270858450.7583@apollo.tec.linutronix.de>

From: Thomas Gleixner <tglx@linutronix.de>
Date: Wed, 27 Feb 2008 09:02:22 +0100 (CET)

> On Tue, 26 Feb 2008, David Miller wrote:
> > What the FUTEX checking code is doing now is doing a "user" access
> > with set_fs(KERNEL_DS) since it runs from the kernel bootup early init
> > sequence.  And this is illegal according to the existing checks.
> > 
> > When we do set_fs(KERNEL_DS) then pass a "user" pointer down
> > into a system call or something like that, we give it a pointer
> > that "cannot fault".  So if we get into the fault handling
> > path here for a case like that we really do want to scream and
> > print out an OOPS message in my opinion.
> 
> So it would be correct to set_fs(USER_DS) then do the check and switch
> back to KERNEL_DS ?

No, I'm saying it would be better not to take faults purposefully in
the kernel address space.  We don't have a usable user address space
setup at this point in the boot, so using USER_DS would be even worse.

I think I'll just add a different version of the sanity check to this
sparc64 code later on, one that will take into consideration this
KERNEL_DS case because I can see how it could be useful in other
circumstances.

> > Did this FUTEX change go into -stable too?
> 
> It's queued, AFAIK

Crap, I'll need to push my fix there too.

  reply	other threads:[~2008-02-27 19:06 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2008-02-25 20:41 Mikael Pettersson
2008-02-26  8:55 ` Mikael Pettersson
2008-02-26 21:32   ` David Miller
2008-02-27  0:49   ` David Miller
2008-02-27  1:06     ` David Miller
2008-02-27  8:02       ` Thomas Gleixner
2008-02-27 19:05         ` David Miller [this message]
2008-02-27 19:55           ` Thomas Gleixner
2008-02-27 19:16       ` Mikael Pettersson
2008-02-27 19:37         ` David Miller
2008-02-27  8:27     ` Mikael Pettersson
2008-02-26 20:46 ` David Miller

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