linux-kernel - Re: [PATCH v2 2/5] memory-hotplug: update mce_bad

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Date:	Fri, 19 Oct 2012 06:42:46 -0700
From:	Dave Hansen <dave@...ux.vnet.ibm.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
CC:	wency@...fujitsu.com, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, rientjes@...gle.com,
	liuj97@...il.com, len.brown@...el.com, benh@...nel.crashing.org,
	paulus@...ba.org, minchan.kim@...il.com,
	kosaki.motohiro@...fujitsu.com, isimatu.yasuaki@...fujitsu.com,
	Christoph Lameter <cl@...ux.com>
Subject: Re: [PATCH v2 2/5] memory-hotplug: update mce_bad_pages when removing
 the memory

On 10/18/2012 03:20 PM, Andrew Morton wrote:
> On Wed, 17 Oct 2012 08:09:55 -0700
> Dave Hansen <dave@...ux.vnet.ibm.com> wrote:
>>> +#ifdef CONFIG_MEMORY_FAILURE
>>> +static void clear_hwpoisoned_pages(struct page *memmap, int nr_pages)
>>> +{
>>> +	int i;
>>> +
>>> +	if (!memmap)
>>> +		return;
>>
>> I guess free_section_usemap() does the same thing.
> 
> What does this observation mean?

sparse_remove_one_section() has an if(ms->section_mem_map) statement.
Inside that if() block is the only place in the function where 'memmap'
can get set.

Currently, sparse_remove_one_section() calls in to free_section_usemap()
ouside of that if() block.  With this patch new call to
clear_hwpoisoned_pages() is done in the same place, both passing 'memmap'.

However, both free_section_usemap() and clear_hwpoisoned_pages() check
'memmap' for NULL and immediately return if so.  That's a bit silly
since it could hide garbage coming back from sparse_decode_mem_map().
Seems like we should just call them both inside that if() block, or
reorganize sparse_remove_one_section(), maybe like this:

void sparse_remove_one_section(struct zone *zone, struct mem_section *ms)
{
        struct page *memmap = NULL;
        unsigned long *usemap = NULL;

        if (!ms->section_mem_map)
		return;

        usemap = ms->pageblock_flags;
        memmap = sparse_decode_mem_map(ms->section_mem_map,
                                                __section_nr(ms));
        ms->section_mem_map = 0;
        ms->pageblock_flags = NULL;

        free_section_usemap(memmap, usemap);
	clear_hwpoisoned_pages(usemap, ...);
}

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