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

Aneesh Kumar K.V
2019-10-05T06:13:22Z

On 10/4/19 2:33 PM, David Hildenbrand wrote:
> On 04.10.19 11:00, David Hildenbrand wrote:
>> On 03.10.19 18:48, Aneesh Kumar K.V wrote:
>>> On 10/1/19 8:33 PM, David Hildenbrand wrote:
>>>> 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@linux.ibm.com>
>>>>>>
>>>>>> 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@intel.com>
>>>>>> Cc: Andrew Morton <akpm@linux-foundation.org>
>>>>>> Cc: Jason Gunthorpe <jgg@ziepe.ca>
>>>>>> Cc: Logan Gunthorpe <logang@deltatee.com>
>>>>>> Cc: Ira Weiny <ira.weiny@intel.com>
>>>>>> Reviewed-by: Pankaj Gupta <pagupta@redhat.com>
>>>>>> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
>>>>>> [ move all pfn-realted declarations into a single line ]
>>>>>> Signed-off-by: David Hildenbrand <david@redhat.com>
>>>>>> ---
>>>>>> 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))
>>>>
>>>
>>> yes, that would be make it much clear.
>>>
>>> But for MEMORY_DEVICE_PRIVATE start_pfn and pfn should be same?
>>
>> Okay, let's recap. We should call add_pages()/__remove_pages()
>> and arch_add_memory()/arch_remove_memory() with the exact same ranges.
>>
>> So with PHYS_PFN(res->start) and PHYS_PFN(resource_size(res)
>>
>> Now, only a subset of the pages gets actually initialized,
>> meaning the NID and the ZONE we read could be stale.
>> That, we have to fix.
>>
>> What about something like this (am I missing something?):
>>
>> From d77b5c50f86570819a437517a897cc40ed29eefb Mon Sep 17 00:00:00 2001
>> From: "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>
>> Date: Fri, 27 Sep 2019 16:02:24 +0530
>> Subject: [PATCH] mm/memunmap: Don't access uninitialized memmap in
>> memunmap_pages()
>>
>> 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 <dan.j.williams@intel.com>
>> Cc: Andrew Morton <akpm@linux-foundation.org>
>> Cc: Jason Gunthorpe <jgg@ziepe.ca>
>> Cc: Logan Gunthorpe <logang@deltatee.com>
>> Cc: Ira Weiny <ira.weiny@intel.com>
>> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
>> [ minimze code changes, rephrase description ]
>> Signed-off-by: David Hildenbrand <david@redhat.com>
>> ---
>> mm/memremap.c | 11 +++++++----
>> 1 file changed, 7 insertions(+), 4 deletions(-)
>>
>> diff --git a/mm/memremap.c b/mm/memremap.c
>> index 557e53c6fb46..8b11c0da345c 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);
>>
>> 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), res->start,
>> + resource_size(res), NULL);
>
> Keeping the PHYS_PFN() calls of course ...
>

That is not different from what I posted right? For MEMORY_DEVICE_PRIVATE

start_pfn = PHYS_PFN(rest->start)

>> } else {
>> arch_remove_memory(nid, res->start, resource_size(res),
>> pgmap_altmap(pgmap));
>>
>
>

-aneesh