Bug#488022: linux-image-2.6.25-2-486: Does not boot on Vortex86SX (BUG: Int 6: CR2 00000000)

I've now been running git. I started with
git clone git://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-2.6.25..y.git

I did a git bisect and found that the commit that introduced the bug is

commit 94aa6550e8668fab1997e2d57a48b22cf68090b2
Author: Thomas Gleixner
Date: Tue May 13 12:31:00 2008 +0200

x86: distangle user disabled TSC from unstable

upstream commit: 9ccc906c97e34fd91dc6aaf5b69b52d824386910

tsc_enabled is set to 0 from the command line switch "notsc" and from
the mark_tsc_unstable code. Seperate those functionalities and replace
tsc_enable with tsc_disable. This makes also the native_sched_clock()
decision when to use TSC understandable.

Preparatory patch to solve the sched_clock() issue on 32 bit.

Signed-off-by: Thomas Gleixner
Signed-off-by: Chris Wright

This commit changes file arch/x86/kernel/tsc_32.c

I tried booting with notsc but I still got "BUG: Int 6: CR2 00000000"

After looking at the commitdiff, I guessed that native_sched_clock() getscalled before tsc_init().
[url]http://git.kernel.org/?p=linux/kernel/git/stable/linux-2.6.25.y.git;a=commitdiff;h=94aa6550e8668fab1997e2d57a48b22cf68090b2[/url]

Prior to the commit native_sched_clock() looked at unitialised tsc_enable which holds 0
so didn't attempt to access a TSC. After the commit native_sched_clock() looks at
unitialised tsc_disable which holds 0 so attempts to access a TSC leading to the BUG:

Starting with a kernel tree from immediately after the faulty commit. I made the following
change which stops the BUG occuring.

*** arch/x86/kernel/tsc_32.c.000 2008-07-30 13:07:57.000000000 +0100
--- arch/x86/kernel/tsc_32.c 2008-07-30 13:09:57.000000000 +0100
*************** unsigned long long native_sched_clock(vo
*** 121,127 ****
* very important for it to be as fast as the platform
* can achive it. )
*/
! if (unlikely(tsc_disabled))
/* No locking but a rare wrong value is not a big deal: */
return (jiffies_64 - INITIAL_JIFFIES) * (1000000000 / HZ);

--- 121,127 ----
* very important for it to be as fast as the platform
* can achive it. )
*/
! if (unlikely(tsc_disabled || !cpu_has_tsc))
/* No locking but a rare wrong value is not a big deal: */
return (jiffies_64 - INITIAL_JIFFIES) * (1000000000 / HZ);

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On Wed, Jul 30, 2008 at 12:49:38PM +0000, bruce robson wrote:[color=blue]
>
> I've now been running git. I started with
> git clone git://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-2.6.25.y.git
>
> I did a git bisect and found that the commit that introduced the bug is
>
> commit 94aa6550e8668fab1997e2d57a48b22cf68090b2
> Author: Thomas Gleixner
> Date: Tue May 13 12:31:00 2008 +0200
>
> x86: distangle user disabled TSC from unstable
>
> upstream commit: 9ccc906c97e34fd91dc6aaf5b69b52d824386910
>
> tsc_enabled is set to 0 from the command line switch "notsc" and from
> the mark_tsc_unstable code. Seperate those functionalities and replace
> tsc_enable with tsc_disable. This makes also the native_sched_clock()
> decision when to use TSC understandable.
>
> Preparatory patch to solve the sched_clock() issue on 32 bit.
>
> Signed-off-by: Thomas Gleixner
> Signed-off-by: Chris Wright
>
> This commit changes file arch/x86/kernel/tsc_32.c[/color]

Great, thanks Bruce! Can you file a bug on bugzilla.kernel.org with
this information and let us know the number so we can track it?

--
dann frazier




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On Thu, Sep 25, 2008 at 01:11:38PM -0600, dann frazier wrote:[color=blue]
> On Wed, Jul 30, 2008 at 12:49:38PM +0000, bruce robson wrote:[color=green]
> >
> > I've now been running git. I started with
> > git clone git://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-2.6.25.y.git
> >
> > I did a git bisect and found that the commit that introduced the bug is
> >
> > commit 94aa6550e8668fab1997e2d57a48b22cf68090b2
> > Author: Thomas Gleixner
> > Date: Tue May 13 12:31:00 2008 +0200
> >
> > x86: distangle user disabled TSC from unstable
> >
> > upstream commit: 9ccc906c97e34fd91dc6aaf5b69b52d824386910
> >
> > tsc_enabled is set to 0 from the command line switch "notsc" and from
> > the mark_tsc_unstable code. Seperate those functionalities and replace
> > tsc_enable with tsc_disable. This makes also the native_sched_clock()
> > decision when to use TSC understandable.
> >
> > Preparatory patch to solve the sched_clock() issue on 32 bit.
> >
> > Signed-off-by: Thomas Gleixner
> > Signed-off-by: Chris Wright
> >
> > This commit changes file arch/x86/kernel/tsc_32.c[/color]
>
> Great, thanks Bruce! Can you file a bug on bugzilla.kernel.org with
> this information and let us know the number so we can track it?[/color]

Bruce, did you pass this upstream or is the bug fixed in current Lenny
or unstable kernel images?

Cheers,
Moritz



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