The patch titled Subject: mm,hwpoison: fix race with compound page allocation has been added to the -mm tree. Its filename is mmhwpoison-fix-race-with-compound-page-allocation.patch

This patch should soon appear at https://ozlabs.org/~akpm/mmots/broken-out/mmhwpoison-fix-race-with-compound-... and later at https://ozlabs.org/~akpm/mmotm/broken-out/mmhwpoison-fix-race-with-compound-...

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------------------------------------------------------ From: Naoya Horiguchi naoya.horiguchi@nec.com Subject: mm,hwpoison: fix race with compound page allocation

When hugetlb page fault (under overcommiting situation) and memory_failure() race, VM_BUG_ON_PAGE() is triggered by the following race:

CPU0: CPU1:

gather_surplus_pages() page = alloc_surplus_huge_page() memory_failure_hugetlb() get_hwpoison_page(page) __get_hwpoison_page(page) get_page_unless_zero(page) zero = put_page_testzero(page) VM_BUG_ON_PAGE(!zero, page) enqueue_huge_page(h, page) put_page(page)

__get_hwpoison_page() only checks page refcount before taking additional one for memory error handling, which is wrong because there's time windows where compound pages have non-zero refcount during initialization.

So make __get_hwpoison_page() check page status a bit more for a few types of compound pages. PageSlab() check is added because otherwise "non anonymous thp" path is wrongly chosen.

Link: https://lkml.kernel.org/r/20210511151016.2310627-2-nao.horiguchi@gmail.com Fixes: ead07f6a867b ("mm/memory-failure: introduce get_hwpoison_page() for consistent refcount handling") Signed-off-by: Naoya Horiguchi naoya.horiguchi@nec.com Reported-by: Muchun Song songmuchun@bytedance.com Cc: Michal Hocko mhocko@suse.com Cc: Mike Kravetz mike.kravetz@oracle.com Cc: Oscar Salvador osalvador@suse.de Cc: Tony Luck tony.luck@intel.com Cc: stable@vger.kernel.org [5.12+] Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

mm/memory-failure.c | 55 +++++++++++++++++++++++++----------------- 1 file changed, 34 insertions(+), 21 deletions(-)

--- a/mm/memory-failure.c~mmhwpoison-fix-race-with-compound-page-allocation +++ a/mm/memory-failure.c @@ -960,30 +960,43 @@ static int __get_hwpoison_page(struct pa { struct page *head = compound_head(page);

- if (!PageHuge(head) && PageTransHuge(head)) { - /* - * Non anonymous thp exists only in allocation/free time. We - * can't handle such a case correctly, so let's give it up. - * This should be better than triggering BUG_ON when kernel - * tries to touch the "partially handled" page. - */ - if (!PageAnon(head)) { - pr_err("Memory failure: %#lx: non anonymous thp\n", - page_to_pfn(page)); - return 0; - } - } + if (PageCompound(page)) { + if (PageSlab(page)) { + return get_page_unless_zero(page); + } else if (PageHuge(head)) { + int ret = 0;

- if (get_page_unless_zero(head)) { - if (head == compound_head(page)) - return 1; - - pr_info("Memory failure: %#lx cannot catch tail\n", - page_to_pfn(page)); - put_page(head); + spin_lock(&hugetlb_lock); + if (!PageHuge(head)) + ret = -EBUSY; + else if (HPageFreed(head) || HPageMigratable(head)) + ret = get_page_unless_zero(head); + spin_unlock(&hugetlb_lock); + return ret; + } else if (PageTransHuge(head)) { + /* + * Non anonymous thp exists only in allocation/free time. We + * can't handle such a case correctly, so let's give it up. + * This should be better than triggering BUG_ON when kernel + * tries to touch the "partially handled" page. + */ + if (!PageAnon(head)) { + pr_err("Memory failure: %#lx: non anonymous thp\n", + page_to_pfn(page)); + return 0; + } + if (get_page_unless_zero(head)) { + if (head == compound_head(page)) + return 1; + pr_info("Memory failure: %#lx cannot catch tail\n", + page_to_pfn(page)); + put_page(head); + } + } + return 0; }

- return 0; + return get_page_unless_zero(page); }

/* _

Patches currently in -mm which might be from naoya.horiguchi@nec.com are

mmhwpoison-fix-race-with-compound-page-allocation.patch mmhwpoison-make-get_hwpoison_page-call-get_any_page.patch