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

[David Hildenbrand]

On 01.10.19 16:57, David Hildenbrand wrote:
> On 01.10.19 16:40, David Hildenbrand wrote:
>> From: "Aneesh Kumar K.V" <aneesh.kumar@xxxxxxxxxxxxx>
>>
>> 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 <dan.j.williams@xxxxxxxxx>
>> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
>> Cc: Jason Gunthorpe <jgg@xxxxxxxx>
>> Cc: Logan Gunthorpe <logang@xxxxxxxxxxxx>
>> Cc: Ira Weiny <ira.weiny@xxxxxxxxx>
>> Reviewed-by: Pankaj Gupta <pagupta@xxxxxxxxxx>
>> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@xxxxxxxxxxxxx>
>> [ move all pfn-realted declarations into a single line ]
>> Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>
>> ---
>>  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.
> 

To be more precise, I wonder if it should actually be

__remove_pages(page_zone(pfn_to_page(start_pfn)), res->start,
               resource_size(res))

IOW, keep calling __remove_pages() with the same parameters but read
nid/zone from the offset one.

Hope some memunmap_pages() expert can clarify.

-- 

Thanks,

David / dhildenb