On Mon 13-09-21 20:43:35, Miaohe Lin wrote: > On 2021/9/13 20:20, David Hildenbrand wrote: > > On 13.09.21 14:12, Michal Hocko wrote: > >> On Mon 13-09-21 19:51:25, Miaohe Lin wrote: > >>> In start_isolate_page_range() undo path, pfn_to_online_page() just checks > >>> the first pfn in a pageblock while __first_valid_page() will traverse the > >>> pageblock until the first online pfn is found. So we may miss the call to > >>> unset_migratetype_isolate() in undo path and pages will remain isolated > >>> unexpectedly. Fix this by calling undo_isolate_page_range() and this will > >>> also help to simplify the code further. > >> > >> I like the clean up part but is this a real problem that requires CC > >> stable? Have you ever seen this to be a real problem? It looks like > >> something based on reading the code. > > I'm sorry but I haven't seen this to be a real problem. It's a theoretical bug. Make it clear in the changelog > > We discussed that it isn't an issue anymore (we never call it on > > memory holes), but might have been an issue on older kernels, back > > when we didn't have the "memory holes" check in the memory offlining > > path in place. > > So is the Cc:stable needed in this case? I do not think so. Even if this was happening in the practice then the practical consequences would be pretty minor, right? (few pageblocks stay isolated thus unavailable). I do realize that the stable tree is in a hoarding mode for quite some years but my general approach has been (in line with the documentation) to mark and backport only fixes that really do matter. -- Michal Hocko SUSE Labs
