On 2019/2/26 21:51, Kirill A. Shutemov wrote: > On Tue, Feb 26, 2019 at 07:18:00PM +0800, zhong jiang wrote: >> From: zhongjiang <zhongjiang@xxxxxxxxxx> >> >> When soft_offline_in_use_page() runs on a thp tail page after pmd is plit, > s/plit/split/ > >> we trigger the following VM_BUG_ON_PAGE(): >> >> Memory failure: 0x3755ff: non anonymous thp >> __get_any_page: 0x3755ff: unknown zero refcount page type 2fffff80000000 >> Soft offlining pfn 0x34d805 at process virtual address 0x20fff000 >> page:ffffea000d360140 count:0 mapcount:0 mapping:0000000000000000 index:0x1 >> flags: 0x2fffff80000000() >> raw: 002fffff80000000 ffffea000d360108 ffffea000d360188 0000000000000000 >> raw: 0000000000000001 0000000000000000 00000000ffffffff 0000000000000000 >> page dumped because: VM_BUG_ON_PAGE(page_ref_count(page) == 0) >> ------------[ cut here ]------------ >> kernel BUG at ./include/linux/mm.h:519! >> >> soft_offline_in_use_page() passed refcount and page lock from tail page to >> head page, which is not needed because we can pass any subpage to >> split_huge_page(). > I don't see a description of what is going wrong and why change will fixed > it. From the description, it appears as it's cosmetic-only change. > > Please elaborate. When soft_offline_in_use_page runs on a thp tail page after pmd is split, and we pass the head page to split_huge_page, Unfortunately, the tail page can be free or count turn into zero. Thanks, zhong jiang
