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Date: Mon, 21 Mar 2022 17:46:48 -0700
From: Yang Shi <shy828301@...il.com>
To: Naoya Horiguchi <naoya.horiguchi@...ux.dev>
Cc: Linux MM <linux-mm@...ck.org>,
Andrew Morton <akpm@...ux-foundation.org>,
Mike Kravetz <mike.kravetz@...cle.com>,
Miaohe Lin <linmiaohe@...wei.com>,
Naoya Horiguchi <naoya.horiguchi@....com>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v5] mm/hwpoison: fix race between hugetlb free/demotion
and memory_failure_hugetlb()
On Thu, Mar 17, 2022 at 10:16 PM Naoya Horiguchi
<naoya.horiguchi@...ux.dev> wrote:
>
> From: Naoya Horiguchi <naoya.horiguchi@....com>
>
> 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 compound_head is called outside hugetlb_lock, so the head is not
> reliable.
>
> So set PageHWPoison flag after passing prechecks. And to detect
> potential violation, this patch also introduces a new action type
> MF_MSG_DIFFERENT_PAGE_SIZE.
>
> Reported-by: Mike Kravetz <mike.kravetz@...cle.com>
> Signed-off-by: Naoya Horiguchi <naoya.horiguchi@....com>
> Signed-off-by: Miaohe Lin <linmiaohe@...wei.com>
> Cc: <stable@...r.kernel.org>
> ---
> ChangeLog v4 -> v5:
> - call TestSetPageHWPoison() when page_handle_poison() fails.
> - call TestSetPageHWPoison() for unhandlable cases (MF_MSG_UNKNOWN and
> MF_MSG_DIFFERENT_PAGE_SIZE).
> - Set PageHWPoison on the head page only when the error page is surely
> a hugepage, otherwise set the flag on the raw page.
> - rebased onto v5.17-rc8-mmotm-2022-03-16-17-42
>
> ChangeLog v3 -> v4:
> - squash with "mm/memory-failure.c: fix race with changing page
> compound again".
> - update patch subject and description based on it.
>
> ChangeLog v2 -> v3:
> - rename the patch because page lock is not the primary factor to
> solve the reported issue.
> - updated description in the same manner.
> - call page_handle_poison() instead of __page_handle_poison() for
> free hugepage case.
> - reorder put_page and unlock_page (thanks to Miaohe Lin)
>
> ChangeLog v1 -> v2:
> - pass subpage to get_hwpoison_huge_page() instead of head page.
> - call compound_head() in hugetlb_lock to avoid race with hugetlb
> demotion/free.
> ---
> mm/hugetlb.c | 8 +++--
> mm/memory-failure.c | 75 +++++++++++++++++++++++++++------------------
> 2 files changed, 51 insertions(+), 32 deletions(-)
>
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index fbf598bbc4e3..d8ef67c049e4 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -6777,14 +6777,16 @@ bool isolate_huge_page(struct page *page, struct list_head *list)
>
> int get_hwpoison_huge_page(struct page *page, bool *hugetlb)
> {
> + struct page *head;
> int ret = 0;
>
> *hugetlb = false;
> spin_lock_irq(&hugetlb_lock);
> - if (PageHeadHuge(page)) {
> + head = compound_head(page);
> + if (PageHeadHuge(head)) {
> *hugetlb = true;
> - if (HPageFreed(page) || HPageMigratable(page))
> - ret = get_page_unless_zero(page);
> + if (HPageFreed(head) || HPageMigratable(head))
> + ret = get_page_unless_zero(head);
> else
> ret = -EBUSY;
> }
> diff --git a/mm/memory-failure.c b/mm/memory-failure.c
> index e939719c0765..9323a5653dec 100644
> --- a/mm/memory-failure.c
> +++ b/mm/memory-failure.c
> @@ -1194,7 +1194,7 @@ static int __get_hwpoison_page(struct page *page, unsigned long flags)
> int ret = 0;
> bool hugetlb = false;
>
> - ret = get_hwpoison_huge_page(head, &hugetlb);
> + ret = get_hwpoison_huge_page(page, &hugetlb);
> if (hugetlb)
> return ret;
>
> @@ -1281,11 +1281,10 @@ static int get_any_page(struct page *p, unsigned long flags)
>
> static int __get_unpoison_page(struct page *page)
> {
> - struct page *head = compound_head(page);
> int ret = 0;
> bool hugetlb = false;
>
> - ret = get_hwpoison_huge_page(head, &hugetlb);
> + ret = get_hwpoison_huge_page(page, &hugetlb);
> if (hugetlb)
> return ret;
>
> @@ -1504,39 +1503,38 @@ static int memory_failure_hugetlb(unsigned long pfn, int flags)
> struct page *head = compound_head(p);
> int res;
> unsigned long page_flags;
> -
> - if (TestSetPageHWPoison(head)) {
> - pr_err("Memory failure: %#lx: already hardware poisoned\n",
> - pfn);
> - res = -EHWPOISON;
> - if (flags & MF_ACTION_REQUIRED)
> - res = kill_accessing_process(current, page_to_pfn(head), flags);
> - return res;
> - }
> -
> - num_poisoned_pages_inc();
> + bool put = false;
> + unsigned long already_hwpoisoned = 0;
>
> 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);
> + if (page_handle_poison(p, true, false)) {
> res = MF_RECOVERED;
> + } else {
> + if (TestSetPageHWPoison(head))
> + already_hwpoisoned = page_to_pfn(head);
> + else
> + num_poisoned_pages_inc();
> + res = MF_FAILED;
> }
> action_result(pfn, MF_MSG_FREE_HUGE, res);
> - return res == MF_RECOVERED ? 0 : -EBUSY;
> + res = res == MF_RECOVERED ? 0 : -EBUSY;
> + goto out;
> } else if (res < 0) {
> + if (TestSetPageHWPoison(p))
> + already_hwpoisoned = pfn;
> + else
> + num_poisoned_pages_inc();
> action_result(pfn, MF_MSG_UNKNOWN, MF_IGNORED);
> - return -EBUSY;
> + res = -EBUSY;
> + goto out;
> }
> }
>
> @@ -1547,21 +1545,31 @@ static int memory_failure_hugetlb(unsigned long pfn, int flags)
> * If this happens just bail out.
> */
> if (!PageHuge(p) || compound_head(p) != head) {
> + if (TestSetPageHWPoison(p))
> + already_hwpoisoned = pfn;
> + else
> + num_poisoned_pages_inc();
> action_result(pfn, MF_MSG_DIFFERENT_PAGE_SIZE, MF_IGNORED);
The commit log says "this patch also introduces a new action type
MF_MSG_DIFFERENT_PAGE_SIZE", but it is not defined in the patch and it
is called here. Did I miss something?
> res = -EBUSY;
> - goto out;
> + goto unlock_page;
> }
>
> page_flags = head->flags;
>
> if (hwpoison_filter(p)) {
> - if (TestClearPageHWPoison(head))
> - num_poisoned_pages_dec();
> - put_page(p);
> + put = true;
> res = -EOPNOTSUPP;
> - goto out;
> + goto unlock_page;
> + }
> +
> + if (TestSetPageHWPoison(head)) {
> + put = true;
> + already_hwpoisoned = page_to_pfn(head);
> + goto unlock_page;
> }
>
> + num_poisoned_pages_inc();
> +
> /*
> * TODO: hwpoison for pud-sized hugetlb doesn't work right now, so
> * simply disable it. In order to make it work properly, we need
> @@ -1574,18 +1582,27 @@ static int memory_failure_hugetlb(unsigned long pfn, int flags)
> if (huge_page_size(page_hstate(head)) > PMD_SIZE) {
> action_result(pfn, MF_MSG_NON_PMD_HUGE, MF_IGNORED);
> res = -EBUSY;
> - goto out;
> + goto unlock_page;
> }
>
> if (!hwpoison_user_mappings(p, pfn, flags, head)) {
> action_result(pfn, MF_MSG_UNMAP_FAILED, MF_IGNORED);
> res = -EBUSY;
> - goto out;
> + goto unlock_page;
> }
>
> return identify_page_state(pfn, p, page_flags);
> -out:
> +unlock_page:
> unlock_page(head);
> +out:
> + if (put)
> + put_page(p);
> + if (already_hwpoisoned) {
> + pr_err("Memory failure: %#lx: already hardware poisoned\n", pfn);
> + res = -EHWPOISON;
> + if (flags & MF_ACTION_REQUIRED)
> + res = kill_accessing_process(current, already_hwpoisoned, flags);
> + }
> return res;
> }
>
> --
> 2.25.1
>
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