On 2019/11/27 22:13, Michal Hocko wrote: > 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. I'm still trying to reproduce it on 4.4 and 5.4, add Catalin, Will Mark, could you give some advice on it, thanks. https://lore.kernel.org/linux-mm/54064878-ea85-247a-3382-b96ddf97c667@xxxxxxxxxx/T/#m87c545730a0a00c45e042937593c59f6552d1246 note: We backport numa patches into 4.4, so the CONFIG_HOLES_IN_ZONE is enabled. # CONFIG_NUMA is not set CONFIG_HOLES_IN_ZONE=y CONFIG_SPARSEMEM_MANUAL=y CONFIG_SPARSEMEM=y CONFIG_HAVE_MEMORY_PRESENT=y CONFIG_SPARSEMEM_EXTREME=y CONFIG_SPARSEMEM_VMEMMAP_ENABLE=y CONFIG_SPARSEMEM_ALLOC_MEM_MAP_TOGETHER=y # CONFIG_SPARSEMEM_VMEMMAP is not set >
