On 01.12.19 00:21, Andrew Morton wrote: > On Sun, 27 Oct 2019 23:45:52 +0100 David Hildenbrand <david@xxxxxxxxxx> wrote: > >> I think I just found an issue with try_offline_node(). >> try_offline_node() is pretty much broken already (touches garbage >> memmaps and will not considers mixed NIDs within sections), however, >> relies on the node span to look for memory sections to probe. So it >> seems to rely on the nodes getting shrunk when removing memory, not when >> offlining. >> >> As we shrink the node span when offlining now and not when removing, >> this can go wrong once we offline the last memory block of the node and >> offline the last CPU. We could still have memory around that we could >> re-online, however, the node would already be offline. Unlikely, but >> possible. >> >> Note that the same is also broken without this patch in case memory is >> never onlined. The "pfn_to_nid(pfn) != nid" can easily succeed on the >> garbage memmap, resulting in no memory being detected as belonging to >> the node. Also, resize_pgdat_range() is called when onlining memory, not >> when adding it. :/ Oh this is so broken :) >> >> The right fix is probably to walk over all memory blocks that could >> exist and test if they belong to the nid (if offline, check the >> block->nid, if online check all pageblocks). A fix we can then move in >> front of this patch. >> >> Will look into this this week. > > And this series shows almost no sign of having been reviewed. I'll hold > it over for 5.6. > Hi Andrew, any chance we can get the (now at least reviewed - thx Oscar) fix in patch #5 into 5.5? (I want to do the final stable backports for the uninitialized memmap stuff) -- Thanks, David / dhildenb
