On Fri 17-01-20 10:42:10, David Hildenbrand wrote: > On 17.01.20 10:40, Michal Hocko wrote: > > On Fri 17-01-20 10:25:06, David Hildenbrand wrote: > >> On 17.01.20 09:59, Michal Hocko wrote: > >>> On Fri 17-01-20 09:51:05, David Hildenbrand wrote: > >>>> On 17.01.20 03:21, Qian Cai wrote: > >>> [...] > >>>>> Even though has_unmovable_pages doesn't hold any reference to the > >>>>> returned page this should be reasonably safe for the purpose of > >>>>> reporting the page (dump_page) because it cannot be hotremoved. The > >>>> > >>>> This is only true in the context of memory unplug, but not in the > >>>> context of is_mem_section_removable()-> is_pageblock_removable_nolock(). > >>> > >>> Well, the above should hold for that path as well AFAICS. If the page is > >>> unmovable then a racing hotplug cannot remove it, right? Or do you > >>> consider a temporary unmovability to be a problem? > >> > >> Somebody could test /sys/devices/system/memory/memoryX/removable. While > >> returning the unmovable page, it could become movable and > >> offlining+removing could succeed. > > > > Doesn't this path use device lock or something? If not than the new code > > is not more racy then the existing one. Just look at > > is_pageblock_removable_nolock and how it dereferences struct page > > (page_zonenum in page_zone.) > > > > AFAIK no device lock, no device hotplug lock, no memory hotplug lock. I > think it holds a reference to the device and to the kernelfs node. But > AFAIK that does not block removal of offlining/memory, just when the > objects get freed. OK, so we are bug compatible after this patch ;) -- Michal Hocko SUSE Labs
