On Mon 19-11-18 17:48:35, Vlastimil Babka wrote: > On 11/19/18 5:46 PM, Vlastimil Babka wrote: > > On 11/19/18 5:46 PM, Michal Hocko wrote: > >> On Mon 19-11-18 17:36:21, Vlastimil Babka wrote: > >>> > >>> So what protects us from locking a page whose refcount dropped to zero? > >>> and is being freed? The checks in freeing path won't be happy about a > >>> stray lock. > >> > >> Nothing really prevents that. But does it matter. The worst that might > >> happen is that we lock a freed or reused page. Who would complain? > > > > free_pages_check() for example > > > > PAGE_FLAGS_CHECK_AT_FREE includes PG_locked
Right you are. > And besides... what about the last page being offlined and then the > whole struct page's part of vmemmap destroyed as the node goes away? Yeah, that is quite unlikely though because the there is quite a large time window between the two events. I am not entirely sure we are safe right now TBH. Any access to the struct page after the put_page is unsafe theoretically. Then we have to come up with something more clever I am afraid. -- Michal Hocko SUSE Labs
