Re: [PATCH v6 01/10] mm/memunmap: Don't access uninitialized memmap in memunmap_pages()

David Hildenbrand
2019-10-06T20:13:50Z

On 06.10.19 21:58, Damian Tometzki wrote:
> Hello David,
>
> patch 05/10 is missing in the patch series.
>

Hi Damian,

not really. Could be that lkml is slow today. E.g., check

https://marc.info/?l=linux-mm&m=157035222620403&w=2

and especially

https://marc.info/?l=linux-mm&m=157035225120440&w=2

All mails popped up on the mm list.

>
> On Sun, 06. Oct 10:56, David Hildenbrand wrote:
>> From: "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>
>>
>> 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..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);
>
> Why we need 'nid = page_to_nid(first_page)' we didnt use it anymore in this function ?

Please see ...

>
>>
>> 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),
^ here

:)

>> pgmap_altmap(pgmap));

--

Thanks,

David / dhildenb