On 2022/8/2 12:07, Muchun Song wrote: > 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]. Oh, I remember I see the race proposed in [1] but I did not look into that carefully at that time. Sorry. > But I didn't think more how to solve it. I hope this thread can find a good solution. :) > > [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. Agree. But I can't find a easy way to fix it yet. > Just a quick reply, no suggestion/solutions from me. Many thanks for your quick reply. > > Thanks. > >> Any response would be appreciated! >> >> Thanks! >> > . >
