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Re: [PATCH] MIPS: Avoid clobbering struct pt_regs in kthreads (v2).

To: David Daney <ddaney@caviumnetworks.com>
Subject: Re: [PATCH] MIPS: Avoid clobbering struct pt_regs in kthreads (v2).
From: Ralf Baechle <ralf@linux-mips.org>
Date: Thu, 9 Jul 2009 01:09:15 +0100
Cc: linux-mips@linux-mips.org
In-reply-to: <20090708174040.GA4069@linux-mips.org>
Original-recipient: rfc822;linux-mips@linux-mips.org
References: <1247072870-14460-1-git-send-email-ddaney@caviumnetworks.com> <20090708174040.GA4069@linux-mips.org>
Sender: linux-mips-bounce@linux-mips.org
User-agent: Mutt/1.5.18 (2008-05-17)
On Wed, Jul 08, 2009 at 06:40:40PM +0100, Ralf Baechle wrote:

> > The resume() implementation octeon_switch.S examines the saved
> > cp0_status register.  We were clobbering the entire pt_regs structure
> > in kernel threads leading to random crashes.
> > 
> > When switching away from a kernel thread, the saved cp0_status is
> > examined and if bit 30 is set it is cleared and the CP2 state saved
> > into the pt_regs structure.  Since the kernel thread stack overlaid
> > the pt_regs structure this resulted in a corrupt stack.  When the
> > kthread with the corrupt stack was resumed, it could crash if it used
> > any of the data in the stack that was clobbered.
> > 
> > We fix it by moving the kernel thread stack down so it doesn't overlay
> > pt_regs.
> > 
> > Differences from v1: Don't adjust the sp by an additional 32 bytes, it
> >                      was not needed.  Also fix up __KSTK_TOS and
> >                      task_pt_regs.
> 
> Thanks for fixing and testing the issues I raised on IRC.  Next I'm wonding
> what impact the uninitialized state of the stack frame we allocate may
> have.  I think we're ok - but I need to stare at this for a few more
> minutes.

Applied :)

  Ralf

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