On Wed 27-11-19 21:13:00, Kefeng Wang wrote: > > > On 2019/11/27 19:47, Michal Hocko wrote: > > On Wed 27-11-19 18:28:00, Kefeng Wang wrote: > >> The start_pfn and end_pfn are already available in move_freepages_block(), > >> pfn_valid_within() should validate pfn first before touching the page, > >> or we might access an unitialized page with CONFIG_HOLES_IN_ZONE configs. > >> > >> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> > >> Cc: Michal Hocko <mhocko@xxxxxxxx> > >> Cc: Vlastimil Babka <vbabka@xxxxxxx> > >> Signed-off-by: Kefeng Wang <wangkefeng.wang@xxxxxxxxxx> > >> --- > >> > >> Here is an oops in 4.4(arm64 enabled CONFIG_HOLES_IN_ZONE), > > > > Is this reproducible with the current upstream kernel? There were large > > changes in this aread since 4.4 > > Our inner tester found this oops twice, but couldn't be reproduced for now, > even in 4.4 kernel, still trying... > > But the page_to_pfn() shouldn't be used in move_freepages(), right? ; ) Well, I do agree that going back and forth between page and pfn is ugly. So this as a cleanup makes sense to me. But you are trying to fix a bug and that bug should be explained. NULL ptr dereference sounds like a memmap is not allocated for the particular pfn and this is a bit unexpected even with holes, at least on x86, maybe arm64 allows that. But the changelog should be clear about all this rather than paper over a deeper problem potentially. Please also make sure to involve arm64 people. -- Michal Hocko SUSE Labs
