The patch titled Subject: mm/hwpoison: fix race between hugetlb free/demotion and memory_failure_hugetlb() has been added to the -mm tree. Its filename is mm-hwpoison-fix-race-between-hugetlb-free-demotion-and-memory_failure_hugetlb.patch

This patch should soon appear at https://ozlabs.org/~akpm/mmots/broken-out/mm-hwpoison-fix-race-between-huget... and later at https://ozlabs.org/~akpm/mmotm/broken-out/mm-hwpoison-fix-race-between-huget...

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------------------------------------------------------ From: Naoya Horiguchi naoya.horiguchi@nec.com Subject: mm/hwpoison: fix race between hugetlb free/demotion and memory_failure_hugetlb()

There is a race condition between memory_failure_hugetlb() and hugetlb free/demotion, which causes setting PageHWPoison flag on the wrong page. The one simple result is that wrong processes can be killed, but another (more serious) one is that the actual error is left unhandled, so no one prevents later access to it, and that might lead to more serious results like consuming corrupted data.

Think about the below race window:

CPU 1 CPU 2 memory_failure_hugetlb struct page *head = compound_head(p); hugetlb page might be freed to buddy, or even changed to another compound page.

get_hwpoison_page -- page is not what we want now...

The current code first does prechecks roughly and then reconfirms after taking refcount, but it's found that it makes code overly complicated, so move the prechecks in a single hugetlb_lock range.

A newly introduced function, try_memory_failure_hugetlb(), always takes hugetlb_lock (even for non-hugetlb pages). That can be improved, but memory_failure() is rare in principle, so should not be a big problem.

Link: https://lkml.kernel.org/r/20220408135323.1559401-2-naoya.horiguchi@linux.dev Fixes: 761ad8d7c7b5 ("mm: hwpoison: introduce memory_failure_hugetlb()") Signed-off-by: Naoya Horiguchi naoya.horiguchi@nec.com Reported-by: Mike Kravetz mike.kravetz@oracle.com Cc: Miaohe Lin linmiaohe@huawei.com Cc: Yang Shi shy828301@gmail.com Cc: Dan Carpenter dan.carpenter@oracle.com Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

include/linux/hugetlb.h | 6 + include/linux/mm.h | 8 ++ mm/hugetlb.c | 10 ++ mm/memory-failure.c | 145 ++++++++++++++++++++++++++------------ 4 files changed, 127 insertions(+), 42 deletions(-)

--- a/include/linux/hugetlb.h~mm-hwpoison-fix-race-between-hugetlb-free-demotion-and-memory_failure_hugetlb +++ a/include/linux/hugetlb.h @@ -169,6 +169,7 @@ long hugetlb_unreserve_pages(struct inod long freed); bool isolate_huge_page(struct page *page, struct list_head *list); int get_hwpoison_huge_page(struct page *page, bool *hugetlb); +int get_huge_page_for_hwpoison(unsigned long pfn, int flags); void putback_active_hugepage(struct page *page); void move_hugetlb_state(struct page *oldpage, struct page *newpage, int reason); void free_huge_page(struct page *page); @@ -377,6 +378,11 @@ static inline int get_hwpoison_huge_page { return 0; } + +static inline int get_huge_page_for_hwpoison(unsigned long pfn, int flags) +{ + return 0; +}

static inline void putback_active_hugepage(struct page *page) { --- a/include/linux/mm.h~mm-hwpoison-fix-race-between-hugetlb-free-demotion-and-memory_failure_hugetlb +++ a/include/linux/mm.h @@ -3197,6 +3197,14 @@ extern int sysctl_memory_failure_recover extern void shake_page(struct page *p); extern atomic_long_t num_poisoned_pages __read_mostly; extern int soft_offline_page(unsigned long pfn, int flags); +#ifdef CONFIG_MEMORY_FAILURE +extern int __get_huge_page_for_hwpoison(unsigned long pfn, int flags); +#else +static inline int __get_huge_page_for_hwpoison(unsigned long pfn, int flags) +{ + return 0; +} +#endif

#ifndef arch_memory_failure static inline int arch_memory_failure(unsigned long pfn, int flags) --- a/mm/hugetlb.c~mm-hwpoison-fix-race-between-hugetlb-free-demotion-and-memory_failure_hugetlb +++ a/mm/hugetlb.c @@ -6782,6 +6782,16 @@ int get_hwpoison_huge_page(struct page * return ret; }

+int get_huge_page_for_hwpoison(unsigned long pfn, int flags) +{ + int ret; + + spin_lock_irq(&hugetlb_lock); + ret = __get_huge_page_for_hwpoison(pfn, flags); + spin_unlock_irq(&hugetlb_lock); + return ret; +} + void putback_active_hugepage(struct page *page) { spin_lock_irq(&hugetlb_lock); --- a/mm/memory-failure.c~mm-hwpoison-fix-race-between-hugetlb-free-demotion-and-memory_failure_hugetlb +++ a/mm/memory-failure.c @@ -1498,50 +1498,113 @@ static int try_to_split_thp_page(struct return 0; }

-static int memory_failure_hugetlb(unsigned long pfn, int flags) +/* + * Called from hugetlb code with hugetlb_lock held. + * + * Return values: + * 0 - free hugepage + * 1 - in-use hugepage + * 2 - not a hugepage + * -EBUSY - the hugepage is busy (try to retry) + * -EHWPOISON - the hugepage is already hwpoisoned + */ +int __get_huge_page_for_hwpoison(unsigned long pfn, int flags) +{ + struct page *page = pfn_to_page(pfn); + struct page *head = compound_head(page); + int ret = 2; /* fallback to normal page handling */ + bool count_increased = false; + + if (!PageHeadHuge(head)) + goto out; + + if (flags & MF_COUNT_INCREASED) { + ret = 1; + count_increased = true; + } else if (HPageFreed(head) || HPageMigratable(head)) { + ret = get_page_unless_zero(head); + if (ret) + count_increased = true; + } else { + ret = -EBUSY; + goto out; + } + + if (TestSetPageHWPoison(head)) { + ret = -EHWPOISON; + goto out; + } + + return ret; +out: + if (count_increased) + put_page(head); + return ret; +} + +#ifdef CONFIG_HUGETLB_PAGE +/* + * Taking refcount of hugetlb pages needs extra care about race conditions + * with basic operations like hugepage allocation/free/demotion. + * So some of prechecks for hwpoison (pinning, and testing/setting + * PageHWPoison) should be done in single hugetlb_lock range. + */ +static int try_memory_failure_hugetlb(unsigned long pfn, int flags, int *hugetlb) { - struct page *p = pfn_to_page(pfn); - struct page *head = compound_head(p); int res; + struct page *p = pfn_to_page(pfn); + struct page *head; unsigned long page_flags; + bool retry = true;

- if (TestSetPageHWPoison(head)) { - pr_err("Memory failure: %#lx: already hardware poisoned\n", - pfn); - res = -EHWPOISON; - if (flags & MF_ACTION_REQUIRED) + *hugetlb = 1; +retry: + res = get_huge_page_for_hwpoison(pfn, flags); + if (res == 2) { /* fallback to normal page handling */ + *hugetlb = 0; + return 0; + } else if (res == -EHWPOISON) { + pr_err("Memory failure: %#lx: already hardware poisoned\n", pfn); + if (flags & MF_ACTION_REQUIRED) { + head = compound_head(p); res = kill_accessing_process(current, page_to_pfn(head), flags); + } return res; + } else if (res == -EBUSY) { + if (retry) { + retry = false; + goto retry; + } + action_result(pfn, MF_MSG_UNKNOWN, MF_IGNORED); + return res; + } + + head = compound_head(p); + lock_page(head); + + if (hwpoison_filter(p)) { + ClearPageHWPoison(head); + res = -EOPNOTSUPP; + goto out; }

num_poisoned_pages_inc();

- if (!(flags & MF_COUNT_INCREASED)) { - res = get_hwpoison_page(p, flags); - if (!res) { - lock_page(head); - if (hwpoison_filter(p)) { - if (TestClearPageHWPoison(head)) - num_poisoned_pages_dec(); - unlock_page(head); - return -EOPNOTSUPP; - } - unlock_page(head); - res = MF_FAILED; - if (__page_handle_poison(p)) { - page_ref_inc(p); - res = MF_RECOVERED; - } - action_result(pfn, MF_MSG_FREE_HUGE, res); - return res == MF_RECOVERED ? 0 : -EBUSY; - } else if (res < 0) { - action_result(pfn, MF_MSG_UNKNOWN, MF_IGNORED); - return -EBUSY; + /* + * Handling free hugepage. The possible race with hugepage allocation + * or demotion can be prevented by PageHWPoison flag. + */ + if (res == 0) { + unlock_page(head); + res = MF_FAILED; + if (__page_handle_poison(p)) { + page_ref_inc(p); + res = MF_RECOVERED; } + action_result(pfn, MF_MSG_FREE_HUGE, res); + return res == MF_RECOVERED ? 0 : -EBUSY; }

- lock_page(head); - /* * The page could have changed compound pages due to race window. * If this happens just bail out. @@ -1554,14 +1617,6 @@ static int memory_failure_hugetlb(unsign

page_flags = head->flags;

- if (hwpoison_filter(p)) { - if (TestClearPageHWPoison(head)) - num_poisoned_pages_dec(); - put_page(p); - res = -EOPNOTSUPP; - goto out; - } - /* * TODO: hwpoison for pud-sized hugetlb doesn't work right now, so * simply disable it. In order to make it work properly, we need @@ -1588,6 +1643,12 @@ out: unlock_page(head); return res; } +#else +static inline int try_memory_failure_hugetlb(unsigned long pfn, int flags, int *hugetlb) +{ + return 0; +} +#endif

static int memory_failure_dev_pagemap(unsigned long pfn, int flags, struct dev_pagemap *pgmap) @@ -1712,6 +1773,7 @@ int memory_failure(unsigned long pfn, in int res = 0; unsigned long page_flags; bool retry = true; + int hugetlb = 0;

if (!sysctl_memory_failure_recovery) panic("Memory failure on page %lx", pfn); @@ -1739,10 +1801,9 @@ int memory_failure(unsigned long pfn, in }

try_again: - if (PageHuge(p)) { - res = memory_failure_hugetlb(pfn, flags); + res = try_memory_failure_hugetlb(pfn, flags, &hugetlb); + if (hugetlb) goto unlock_mutex; - }

if (TestSetPageHWPoison(p)) { pr_err("Memory failure: %#lx: already hardware poisoned\n", _

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

mm-hwpoison-fix-race-between-hugetlb-free-demotion-and-memory_failure_hugetlb.patch revert-mm-memory-failurec-fix-race-with-changing-page-compound-again.patch