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

David Hildenbrand
2019-10-04T09:03:41Z

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 ...

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

--

Thanks,

David / dhildenb