Re: [PATCH] memcgroup: check and initialize page->cgroup inmemmap_init_zone

[Andrew Morton]

On Fri, 18 Apr 2008 10:46:30 +0800 Shi Weihua <shiwh@xxxxxxxxxxxxxx> wrote:

> When we test memory controller in Fujitsu PrimeQuest(arch: ia64),
> the compiled kernel boots failed, the following message occured on
> the telnet terminal.
> -------------------------------------
> ..........
> ELILO boot: Uncompressing Linux... done
> Loading file initrd-2.6.25-rc9-00067-gb87e81e.img...done
> _ (system freezed)
> -------------------------------------
> 
> We found commit 9442ec9df40d952b0de185ae5638a74970388e01
> causes this boot failure by git-bisect.
> And, we found the following change caused the boot failure.
> -------------------------------------
> @@ -2528,7 +2535,6 @@ void __meminit memmap_init_zone(unsigned long size, int nid, unsigned long zon
>                 set_page_links(page, zone, nid, pfn);
>                 init_page_count(page);
>                 reset_page_mapcount(page);
> -               page_assign_page_cgroup(page, NULL);
>                 SetPageReserved(page);
> 
>                 /*
> -------------------------------------
> In this patch, the Author Hugh Dickins said 
> "...memmap_init_zone doesn't need it either, ...
> Linux assumes pointers in zeroed structures are NULL pointers."
> But it seems it's not always the case, so we should check and initialize
> page->cgroup anyways.
> 
> Signed-off-by: Shi Weihua <shiwh@xxxxxxxxxxxxxx> 
> ---
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 402a504..506d4cf 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -2518,6 +2518,7 @@ void __meminit memmap_init_zone(unsigned long size, int nid, unsigned long zone,
>  	struct page *page;
>  	unsigned long end_pfn = start_pfn + size;
>  	unsigned long pfn;
> +	void *pc;
>  
>  	for (pfn = start_pfn; pfn < end_pfn; pfn++) {
>  		/*
> @@ -2535,6 +2536,9 @@ void __meminit memmap_init_zone(unsigned long size, int nid, unsigned long zone,
>  		set_page_links(page, zone, nid, pfn);
>  		init_page_count(page);
>  		reset_page_mapcount(page);
> +		pc = page_get_page_cgroup(page);
> +		if (pc) 
> +			page_reset_bad_cgroup(page);
>  		SetPageReserved(page);
>  

hm, fishy.  Perhaps the architecture isn't zeroing the memmap arrays?

Or perhaps that page was used and then later freed before we got to
memmap_init_zone() and was freed with a non-zero ->page_cgroup.  Which is
unlikely given that page.page_cgroup was only just added and is only
present if CONFIG_CGROUP_MEM_RES_CTLR.
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