Subject: Re: [PATCH v6 01/10] mm/memunmap: Don't access uninitialized memmap in memunmap_pages()

From: David Hildenbrand <[email-masked]>
Date: Sun, 6 Oct 2019 22:13:39 +0200

On 06.10.19 21:58, Damian Tometzki wrote:
> Hello David,
> 
> patch 05/10 is missing in the patch series. 
> 

Hi Damian,

not really. Could be that lkml is slow today. E.g., check

https://marc.info/?l=linux-mm&m=157035222620403&w=2

and especially

https://marc.info/?l=linux-mm&m=157035225120440&w=2

All mails popped up on the mm list.

> 
> On Sun, 06. Oct 10:56, David Hildenbrand wrote:
>> From: "Aneesh Kumar K.V" <[email-masked]>
>>
>> With an altmap, the memmap falling into the reserved altmap space are
>> not initialized and, therefore, contain a garbage NID and a garbage
>> zone. Make sure to read the NID/zone from a memmap that was initialzed.
>>
>> 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]>
>> Signed-off-by: Aneesh Kumar K.V <[email-masked]>
>> [ minimze code changes, rephrase description ]
>> Signed-off-by: David Hildenbrand <[email-masked]>
>> ---
>>  mm/memremap.c | 11 +++++++----
>>  1 file changed, 7 insertions(+), 4 deletions(-)
>>
>> diff --git a/mm/memremap.c b/mm/memremap.c
>> index 557e53c6fb46..8c2fb44c3b4d 100644
>> --- a/mm/memremap.c
>> +++ b/mm/memremap.c
>> @@ -123,6 +123,7 @@ static void dev_pagemap_cleanup(struct dev_pagemap *pgmap)
>>  void memunmap_pages(struct dev_pagemap *pgmap)
>>  {
>>  	struct resource *res = &pgmap->res;
>> +	struct page *first_page;
>>  	unsigned long pfn;
>>  	int nid;
>>  
>> @@ -131,14 +132,16 @@ void memunmap_pages(struct dev_pagemap *pgmap)
>>  		put_page(pfn_to_page(pfn));
>>  	dev_pagemap_cleanup(pgmap);
>>  
>> +	/* make sure to access a memmap that was actually initialized */
>> +	first_page = pfn_to_page(pfn_first(pgmap));
>> +
>>  	/* pages are dead and unused, undo the arch mapping */
>> -	nid = page_to_nid(pfn_to_page(PHYS_PFN(res->start)));
>> +	nid = page_to_nid(first_page);
> 
> Why we need 'nid = page_to_nid(first_page)' we didnt use it anymore in this function ?

Please see ...

> 
>>  
>>  	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(first_page), PHYS_PFN(res->start),
>> +			       PHYS_PFN(resource_size(res)), NULL);
>>  	} else {
>>  		arch_remove_memory(nid, res->start, resource_size(res),
                                   ^ here

:)

>>  				pgmap_altmap(pgmap));

-- 

Thanks,

David / dhildenb

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