linux-kernel - Re: 2.6.18-mm2 boot failure on x86-64

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Date:	Mon, 9 Oct 2006 10:53:58 +0100 (IST)
From:	Mel Gorman <mel@....ul.ie>
To:	Vivek Goyal <vgoyal@...ibm.com>
Cc:	Steve Fox <drfickle@...ibm.com>, Andi Kleen <ak@...e.de>,
	Badari Pulavarty <pbadari@...ibm.com>,
	Martin Bligh <mbligh@...igh.org>,
	Andrew Morton <akpm@...l.org>,
	lkml <linux-kernel@...r.kernel.org>, netdev@...r.kernel.org,
	kmannth@...ibm.com, Andy Whitcroft <apw@...dowen.org>
Subject: Re: 2.6.18-mm2 boot failure on x86-64

On Fri, 6 Oct 2006, Vivek Goyal wrote:

> On Fri, Oct 06, 2006 at 01:03:50PM -0500, Steve Fox wrote:
>> On Fri, 2006-10-06 at 18:11 +0100, Mel Gorman wrote:
>>> On (06/10/06 11:36), Vivek Goyal didst pronounce:
>>>> Where is bss placed in physical memory? I guess bss_start and bss_stop
>>>> from System.map will tell us. That will confirm that above memset step is
>>>> stomping over bss. Then we have to just find that somewhere probably
>>>> we allocated wrong physical memory area for bootmem allocator map.
>>>>
>>>
>>> BSS is at 0x643000 -> 0x777BC4
>>> init_bootmem wipes from 0x777000 -> 0x8F7000
>>>
>>> So the BSS bytes from 0x777000 ->0x777BC4 (which looks very suspiciously
>>> pile a page alignment of addr & PAGE_MASK) gets set to 0xFF. One possible
>>> fix is below. It adds a check in bad_addr() to see if the BSS section is
>>> about to be used for bootmap. It Seems To Work For Me (tm) and illustrates
>>> the source of the problem even if it's not the 100% correct fix.
>>
>> I was able to boot the machine with Mel's patch applied on top of
>> -git22.
>
>
> Please have a look at the attached patch. Does it make some sense.
>

It makes some sense. As you state, it wastes memory but that is better 
than breaking.

> Steve, can you please give this patch a try if it fixes the problem?
>

I boottested the patch on the same machine as Steve was using and it 
completed successfully.

> Thanks
> Vivek
>
>
>
>
> o Currently some code pieces assume that address returned by find_e820_area()
>  are page aligned. But looks like find_e820_area() had no such intention
>  and hence one might end up stomping over some of the data. One such
>  case is bootmem allocator initialization code stomped over bss.
>
> o This patch modified find_e820_area() to return page aligned address. This
>  might be little wasteful of memory but at the same time probably it is
>  easier to handle page aligned memory.
>
> Signed-off-by: Vivek Goyal <vgoyal@...ibm.com>
> ---
>
> arch/x86_64/kernel/e820.c |   14 +++++++-------
> 1 file changed, 7 insertions(+), 7 deletions(-)
>
> diff -puN arch/x86_64/kernel/e820.c~x86_64-return-page-aligned-phy-addr-from-find-e820-area arch/x86_64/kernel/e820.c
> --- linux-2.6.19-rc1-1M/arch/x86_64/kernel/e820.c~x86_64-return-page-aligned-phy-addr-from-find-e820-area	2006-10-06 15:28:13.000000000 -0400
> +++ linux-2.6.19-rc1-1M-root/arch/x86_64/kernel/e820.c	2006-10-06 15:44:45.000000000 -0400
> @@ -54,13 +54,13 @@ static inline int bad_addr(unsigned long
>
> 	/* various gunk below that needed for SMP startup */
> 	if (addr < 0x8000) {
> -		*addrp = 0x8000;
> +		*addrp = PAGE_ALIGN(0x8000);
> 		return 1;
> 	}
>
> 	/* direct mapping tables of the kernel */
> 	if (last >= table_start<<PAGE_SHIFT && addr < table_end<<PAGE_SHIFT) {
> -		*addrp = table_end << PAGE_SHIFT;
> +		*addrp = PAGE_ALIGN(table_end << PAGE_SHIFT);
> 		return 1;
> 	}
>
> @@ -68,18 +68,18 @@ static inline int bad_addr(unsigned long
> #ifdef CONFIG_BLK_DEV_INITRD
> 	if (LOADER_TYPE && INITRD_START && last >= INITRD_START &&
> 	    addr < INITRD_START+INITRD_SIZE) {
> -		*addrp = INITRD_START + INITRD_SIZE;
> +		*addrp = PAGE_ALIGN(INITRD_START + INITRD_SIZE);
> 		return 1;
> 	}
> #endif
> 	/* kernel code */
> -	if (last >= __pa_symbol(&_text) && last < __pa_symbol(&_end)) {
> -		*addrp = __pa_symbol(&_end);
> +	if (last >= __pa_symbol(&_text) && addr < __pa_symbol(&_end)) {
> +		*addrp = PAGE_ALIGN(__pa_symbol(&_end));
> 		return 1;
> 	}
>
> 	if (last >= ebda_addr && addr < ebda_addr + ebda_size) {
> -		*addrp = ebda_addr + ebda_size;
> +		*addrp = PAGE_ALIGN(ebda_addr + ebda_size);
> 		return 1;
> 	}
>
> @@ -152,7 +152,7 @@ unsigned long __init find_e820_area(unsi
> 			continue;
> 		while (bad_addr(&addr, size) && addr+size <= ei->addr+ei->size)
> 			;
> -		last = addr + size;
> +		last = PAGE_ALIGN(addr) + size;
> 		if (last > ei->addr + ei->size)
> 			continue;
> 		if (last > end)
> _
>

-- 
Mel Gorman
Part-time Phd Student                          Linux Technology Center
University of Limerick                         IBM Dublin Software Lab
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