Re: [PATCH 1/2] mm/memunmap: Use the correct start and end pfn when removing pages from zone

From: "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>
To: David Hildenbrand <david@redhat.com>,
	dan.j.williams@intel.com, akpm@linux-foundation.org
Cc: linux-mm@kvack.org, linux-nvdimm@lists.01.org
Subject: Re: [PATCH 1/2] mm/memunmap: Use the correct start and end pfn when removing pages from zone
Date: Thu, 26 Sep 2019 18:45:19 +0530	[thread overview]
Message-ID: <fcf2e9ee-c93b-8239-f165-0e92138faff0@linux.ibm.com> (raw)
In-Reply-To: <a9aaf327-2e36-618b-9ded-9800f3e6b73f@redhat.com>

On 9/26/19 6:13 PM, David Hildenbrand wrote:
> On 26.09.19 14:25, Aneesh Kumar K.V wrote:
>> 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 namespace.
>>
>> [   74.745056] BUG: Unable to handle kernel data access at 0xc00c000001400000
>> [   74.745256] Faulting instruction address: 0xc0000000000b58b0
>> cpu 0x2: Vector: 300 (Data Access) at [c00000026ea93580]
>>      pc: c0000000000b58b0: memset+0x68/0x104
>>      lr: c0000000003eb008: page_init_poison+0x38/0x50
>>      ...
>>    current = 0xc000000271c67d80
>>    paca    = 0xc00000003fffd680   irqmask: 0x03   irq_happened: 0x01
>>      pid   = 3665, comm = ndctl
>> [link register   ] c0000000003eb008 page_init_poison+0x38/0x50
>> [c00000026ea93830] c0000000004754d4 remove_pfn_range_from_zone+0x64/0x3e0
>> [c00000026ea938a0] c0000000004b8a60 memunmap_pages+0x300/0x400
>> [c00000026ea93930] c0000000009e32a0 devm_action_release+0x30/0x50
>> ...
>>
>> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
>> ---
>>   mm/memremap.c | 15 ++++++++++-----
>>   1 file changed, 10 insertions(+), 5 deletions(-)
>>
>> diff --git a/mm/memremap.c b/mm/memremap.c
>> index 390bb3544589..76b98110031e 100644
>> --- a/mm/memremap.c
>> +++ b/mm/memremap.c
>> @@ -113,7 +113,8 @@ static void dev_pagemap_cleanup(struct dev_pagemap *pgmap)
>>   void memunmap_pages(struct dev_pagemap *pgmap)
>>   {
>>   	struct resource *res = &pgmap->res;
>> -	unsigned long pfn = PHYS_PFN(res->start);
>> +	unsigned long start_pfn, end_pfn;
>> +	unsigned long pfn, nr_pages;
>>   	int nid;
>>   
>>   	dev_pagemap_kill(pgmap);
>> @@ -121,14 +122,18 @@ 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(pfn));
>> +	nid = page_to_nid(pfn_to_page(start_pfn));
>>   
>>   	mem_hotplug_begin();
>> -	remove_pfn_range_from_zone(page_zone(pfn_to_page(pfn)), pfn,
>> -				   PHYS_PFN(resource_size(res)));
>> +	remove_pfn_range_from_zone(page_zone(pfn_to_page(start_pfn)),
>> +				   start_pfn, nr_pages);
>>   	if (pgmap->type == MEMORY_DEVICE_PRIVATE) {
>> -		__remove_pages(pfn, PHYS_PFN(resource_size(res)), NULL);
>> +		__remove_pages(start_pfn, nr_pages, NULL);
>>   	} else {
>>   		arch_remove_memory(nid, res->start, resource_size(res),
>>   				pgmap_altmap(pgmap));
>>
> 
> Just to make sure, my patches did not break that, right (IOW, broken
> upstream)?
> 

That is correct. Your patches helped to remove other usages of wrong 
pfns. The last few left got fixed in this patch.

-aneesh
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