On 10.03.20 12:59, Michal Hocko wrote:
> On Tue 10-03-20 12:46:05, David Hildenbrand wrote:
>> On 10.03.20 12:43, Michal Hocko wrote:
>>> On Mon 02-03-20 14:49:37, David Hildenbrand wrote:
>>> [...]
>>>> +static void virtio_mem_notify_going_offline(struct virtio_mem *vm,
>>>> + unsigned long mb_id)
>>>> +{
>>>> + const unsigned long nr_pages = PFN_DOWN(vm->subblock_size);
>>>> + unsigned long pfn;
>>>> + int sb_id, i;
>>>> +
>>>> + for (sb_id = 0; sb_id < vm->nb_sb_per_mb; sb_id++) {
>>>> + if (virtio_mem_mb_test_sb_plugged(vm, mb_id, sb_id, 1))
>>>> + continue;
>>>> + /*
>>>> + * Drop our reference to the pages so the memory can get
>>>> + * offlined and add the unplugged pages to the managed
>>>> + * page counters (so offlining code can correctly subtract
>>>> + * them again).
>>>> + */
>>>> + pfn = PFN_DOWN(virtio_mem_mb_id_to_phys(mb_id) +
>>>> + sb_id * vm->subblock_size);
>>>> + adjust_managed_page_count(pfn_to_page(pfn), nr_pages);
>>>> + for (i = 0; i < nr_pages; i++)
>>>> + page_ref_dec(pfn_to_page(pfn + i));
>>>
>>> Is there ever situation this might be a different than 1->0 transition?
>>
>> Only if some other code would be taking a reference. At least not from
>> virtio-mem perspective.
>
> OK, so that is essentially an error condition. I think it shouldn't go
> silent and you want something like
> if (WARN_ON(!page_ref_sub_and_test(page)))
> dump_page(pfn_to_page(pfn + i), "YOUR REASON");
>
Makes sense - I'll most probably convert this to a WARN_ON_ONCE.
Thanks!
--
Thanks,
David / dhildenb
