linux-kernel - Re: [1/2] 2.6.22-rc5: known regressions with patches

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Message-ID: <20070621071125.GA6615@in.ibm.com>
Date:	Thu, 21 Jun 2007 12:41:25 +0530
From:	"S. P. Prasanna" <prasanna@...ibm.com>
To:	Arjan van de Ven <arjan@...radead.org>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ian McDonald <ian.mcdonald@...di.co.nz>,
	Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Miklos Szeredi <miklos@...redi.hu>,
	Ingo Molnar <mingo@...e.hu>,
	"Darrick J. Wong" <djwong@...ibm.com>, Andi Kleen <ak@...e.de>,
	Bj?rn Steinbrink <B.Steinbrink@....de>,
	William Cohen <wcohen@...hat.com>,
	Antonino Daplas <adaplas@...il.com>,
	Olaf Hering <olaf@...fle.de>, Ville Syrj?l? <syrjala@....fi>,
	Jean Delvare <khali@...ux-fr.org>,
	Rudolf Marek <r.marek@...embler.cz>,
	Soeren Sonnenburg <kernel@....de>,
	Michal Piotrowski <michal.k.k.piotrowski@...il.com>
Subject: Re: [1/2] 2.6.22-rc5: known regressions with patches

On Wed, Jun 20, 2007 at 10:23:21PM -0700, Arjan van de Ven wrote:
> On Wed, 2007-06-20 at 16:50 -0700, Linus Torvalds wrote:
> > 
> > On Wed, 20 Jun 2007, Arjan van de Ven wrote:
> > > 
> > > the real fix would be something like this instead:
> > 
> > If people can test this, and confirm it works, please send a patch that 
> > not only does this ad undoes the Kconfig language.  It looks like the 
> > right thing to do, but I won't touch it without somebody who actually 
> > tested these combinarions sending in a patch.
> 
> Hi,
> 
> I have tested this on x86_64, and without the config language, the
> original oopses, while with the patch below it works fine (as expected).
> I've not been able to test the i386 one (no 32 bit testboxes since 2
> years) but the change is even simpler there, just an ifdef around the
> entire kernel text marking.

I tested this patch on i386 box, it seems to work fine.

Thanks
Prasanna
> 
> 
> 
> Do not mark the kernel text read only if KPROBES is in the kernel;
> kprobes needs to hot-patch the kernel text to insert it's
> instrumentation. In this case, only mark the .rodata segment as read
> only.
> 
> Signed-off-by: Arjan van de Ven <arjan@...ux.intel.com>
> 
> --- linux-2.6.22-rc5/arch/i386/Kconfig.debug.org	2007-06-20 22:20:30.000000000 -0700
> +++ linux-2.6.22-rc5/arch/i386/Kconfig.debug	2007-06-20 22:20:55.000000000 -0700
> @@ -49,7 +49,6 @@ config DEBUG_PAGEALLOC
>  config DEBUG_RODATA
>  	bool "Write protect kernel read-only data structures"
>  	depends on DEBUG_KERNEL
> -	depends on !KPROBES # temporary for 2.6.22
>  	help
>  	  Mark the kernel read-only data as write-protected in the pagetables,
>  	  in order to catch accidental (and incorrect) writes to such const
> --- linux-2.6.22-rc5/arch/x86_64/Kconfig.debug.org	2007-06-20 22:20:28.000000000 -0700
> +++ linux-2.6.22-rc5/arch/x86_64/Kconfig.debug	2007-06-20 22:20:44.000000000 -0700
> @@ -9,7 +9,6 @@ source "lib/Kconfig.debug"
>  config DEBUG_RODATA
>         bool "Write protect kernel read-only data structures"
>         depends on DEBUG_KERNEL
> -       depends on !KPROBES # temporary for 2.6.22
>         help
>  	 Mark the kernel read-only data as write-protected in the pagetables,
>  	 in order to catch accidental (and incorrect) writes to such const data.
> --- linux-2.6.22-rc5/arch/i386/mm/init.c.org	2007-06-20 22:18:40.000000000 -0700
> +++ linux-2.6.22-rc5/arch/i386/mm/init.c	2007-06-20 22:19:45.000000000 -0700
> @@ -799,6 +799,7 @@ void mark_rodata_ro(void)
>  	unsigned long start = PFN_ALIGN(_text);
>  	unsigned long size = PFN_ALIGN(_etext) - start;
> 
> +#ifndef CONFIG_KPROBES
>  #ifdef CONFIG_HOTPLUG_CPU
>  	/* It must still be possible to apply SMP alternatives. */
>  	if (num_possible_cpus() <= 1)
> @@ -808,7 +809,7 @@ void mark_rodata_ro(void)
>  		                 size >> PAGE_SHIFT, PAGE_KERNEL_RX);
>  		printk("Write protecting the kernel text: %luk\n", size >> 10);
>  	}
> -
> +#endif
>  	start += size;
>  	size = (unsigned long)__end_rodata - start;
>  	change_page_attr(virt_to_page(start),
> --- linux-2.6.22-rc5/arch/x86_64/mm/init.c.org	2007-06-20 21:44:15.000000000 -0700
> +++ linux-2.6.22-rc5/arch/x86_64/mm/init.c	2007-06-20 22:17:45.000000000 -0700
> @@ -605,6 +605,11 @@ void mark_rodata_ro(void)
>  	if (num_possible_cpus() > 1)
>  		start = (unsigned long)_etext;
>  #endif
> +
> +#ifdef CONFIG_KPROBES
> +	start = (unsigned long)__start_rodata;
> +#endif
> +	
>  	end = (unsigned long)__end_rodata;
>  	start = (start + PAGE_SIZE - 1) & PAGE_MASK;
>  	end &= PAGE_MASK;
> 
> -- 
> if you want to mail me at work (you don't), use arjan (at) linux.intel.com
> Test the interaction between Linux and your BIOS via http://www.linuxfirmwarekit.org

-- 
Thanks & Regards
Prasanna S.P.
Linux Technology Center
India Software Labs, IBM Bangalore
Email: prasanna@...ibm.com
Ph: 91-80-41776329
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