On Tue, Aug 02, 2022 at 10:00:50AM +0800, Miaohe Lin wrote: > Hi all: > When I investigate the mm/memory-failure.c code again, I found there's a possible race window > between memory_failure and alloc_fresh_huge_page/free_huge_page. Thank about the below scene: > > CPU 1 CPU 2 > alloc_fresh_huge_page -- page refcnt > 0 memory_failure > prep_new_huge_page get_huge_page_for_hwpoison > !PageHeadHuge -- so 2(not a hugepage) is returned > hugetlb_vmemmap_optimize -- subpages is read-only > set_compound_page_dtor -- PageHuge is true now, but too late!!! > TestSetPageHWPoison(p) > -- We might write to read-only subpages here!!! > > Another similar scene: > > CPU 1 CPU 2 > free_huge_page -- page refcnt == 0 and not PageHuge memory_failure > get_huge_page_for_hwpoison > !PageHeadHuge -- so 2(not a hugepage) is returned > TestSetPageHWPoison(p) > -- We might write to read-only subpages here!!! > hugetlb_vmemmap_restore -- subpages can be written to now, but too late!!! > I agree this race is possible, I have proposed this race in thread [1]. But I didn't think more how to solve it. [1] https://lore.kernel.org/linux-mm/20220623235153.2623702-1-naoya.horiguchi@xxxxxxxxx/T/#ma094a7cea7df8fd9a77a91551bf39077d89e23bd > I think the above scenes are possible. But I can't found a stable solution to fix it. Any suggestions? > Or is it not worth to fix it as it's too rare? Or am I miss something? > Luckily, the system will panic at once, which encountering this race. However, we don't see any bug report. If we have an easy way to fix it, I think it is worth. Just a quick reply, no suggestion/solutions from me. Thanks. > Any response would be appreciated! > > Thanks! >
