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

David Hildenbrand
2019-10-06T08:13:49Z

On 05.10.19 08:13, Aneesh Kumar K.V wrote:
> 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

I'll go with this modified patch for now, which does not change the ranges
passed to __remove_pages(), because that looked like a unrelated change to me.
__remove_ages() has to be called with the same range as add_pages().

commit f66c2fa09293ae0f99afc4363146941579152409 (HEAD)
Author: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
Date: Fri Sep 27 16:02:24 2019 +0530

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>

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);

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),
pgmap_altmap(pgmap));

As Andrew wants to give this some testing, I'll send out a new version
shortly, then we can discuss there.

--

Thanks,

David / dhildenb