Subject: Re: [PATCH v5 01/10] mm/memunmap: Use the correct start and end pfn when removing pages from zone

From: David Hildenbrand <[email-masked]>
Date: Tue, 1 Oct 2019 16:57:54 +0200

On 01.10.19 16:40, David Hildenbrand wrote:
> From: "Aneesh Kumar K.V" <[email-masked]>
> 
> With altmap, all the resource pfns are not initialized. While initializing
> pfn, altmap reserve space is skipped. Hence when removing pfn from zone
> skip pfns that were never initialized.
> 
> Update memunmap_pages to calculate start and end pfn based on altmap
> values. This fixes a kernel crash that is observed when destroying
> a namespace.
> 
> [   81.356173] kernel BUG at include/linux/mm.h:1107!
> cpu 0x1: Vector: 700 (Program Check) at [c000000274087890]
>     pc: c0000000004b9728: memunmap_pages+0x238/0x340
>     lr: c0000000004b9724: memunmap_pages+0x234/0x340
> ...
>     pid   = 3669, comm = ndctl
> kernel BUG at include/linux/mm.h:1107!
> [c000000274087ba0] c0000000009e3500 devm_action_release+0x30/0x50
> [c000000274087bc0] c0000000009e4758 release_nodes+0x268/0x2d0
> [c000000274087c30] c0000000009dd144 device_release_driver_internal+0x174/0x240
> [c000000274087c70] c0000000009d9dfc unbind_store+0x13c/0x190
> [c000000274087cb0] c0000000009d8a24 drv_attr_store+0x44/0x60
> [c000000274087cd0] c0000000005a7470 sysfs_kf_write+0x70/0xa0
> [c000000274087d10] c0000000005a5cac kernfs_fop_write+0x1ac/0x290
> [c000000274087d60] c0000000004be45c __vfs_write+0x3c/0x70
> [c000000274087d80] c0000000004c26e4 vfs_write+0xe4/0x200
> [c000000274087dd0] c0000000004c2a6c ksys_write+0x7c/0x140
> [c000000274087e20] c00000000000bbd0 system_call+0x5c/0x68
> 
> Cc: Dan Williams <[email-masked]>
> Cc: Andrew Morton <[email-masked]>
> Cc: Jason Gunthorpe <[email-masked]>
> Cc: Logan Gunthorpe <[email-masked]>
> Cc: Ira Weiny <[email-masked]>
> Reviewed-by: Pankaj Gupta <[email-masked]>
> Signed-off-by: Aneesh Kumar K.V <[email-masked]>
> [ move all pfn-realted declarations into a single line ]
> Signed-off-by: David Hildenbrand <[email-masked]>
> ---
>  mm/memremap.c | 13 ++++++++-----
>  1 file changed, 8 insertions(+), 5 deletions(-)
> 
> diff --git a/mm/memremap.c b/mm/memremap.c
> index 557e53c6fb46..026788b2ac69 100644
> --- a/mm/memremap.c
> +++ b/mm/memremap.c
> @@ -123,7 +123,7 @@ static void dev_pagemap_cleanup(struct dev_pagemap *pgmap)
>  void memunmap_pages(struct dev_pagemap *pgmap)
>  {
>  	struct resource *res = &pgmap->res;
> -	unsigned long pfn;
> +	unsigned long pfn, nr_pages, start_pfn, end_pfn;
>  	int nid;
>  
>  	dev_pagemap_kill(pgmap);
> @@ -131,14 +131,17 @@ void memunmap_pages(struct dev_pagemap *pgmap)
>  		put_page(pfn_to_page(pfn));
>  	dev_pagemap_cleanup(pgmap);
>  
> +	start_pfn = pfn_first(pgmap);
> +	end_pfn = pfn_end(pgmap);
> +	nr_pages = end_pfn - start_pfn;
> +
>  	/* pages are dead and unused, undo the arch mapping */
> -	nid = page_to_nid(pfn_to_page(PHYS_PFN(res->start)));
> +	nid = page_to_nid(pfn_to_page(start_pfn));
>  
>  	mem_hotplug_begin();
>  	if (pgmap->type == MEMORY_DEVICE_PRIVATE) {
> -		pfn = PHYS_PFN(res->start);
> -		__remove_pages(page_zone(pfn_to_page(pfn)), pfn,
> -				 PHYS_PFN(resource_size(res)), NULL);
> +		__remove_pages(page_zone(pfn_to_page(start_pfn)), start_pfn,
> +			       nr_pages, NULL);
>  	} else {
>  		arch_remove_memory(nid, res->start, resource_size(res),
>  				pgmap_altmap(pgmap));
> 

Aneesh, I was wondering why the use of "res->start" is correct (and we
shouldn't also witch to start_pfn/nr_pages here. It would be good if Dan
could review.

-- 

Thanks,

David / dhildenb

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