> On Nov 27, 2019, at 9:39 AM, Kefeng Wang <wangkefeng.wang@xxxxxxxxxx> wrote: > > > > 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 See the commit b13bc35193d9 (“mm/hotplug: invalid PFNs from pfn_to_online_page()”) where it lists a lot of code churn in that space that might indicate there are many commits missing in your kernel.
