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Message-ID: <CAHbLzkoCUs-Z9m47SnF3sR-wai3_M6R4Jkxq8bNBTdoTrkh5vA@mail.gmail.com>
Date: Mon, 8 Nov 2021 15:27:55 -0800
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>,
David Hildenbrand <david@...hat.com>,
Oscar Salvador <osalvador@...e.de>,
Michal Hocko <mhocko@...e.com>,
Ding Hui <dinghui@...gfor.com.cn>,
Tony Luck <tony.luck@...el.com>,
"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
Miaohe Lin <linmiaohe@...wei.com>,
Peter Xu <peterx@...hat.com>,
Naoya Horiguchi <naoya.horiguchi@....com>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 3/3] mm/hwpoison: fix unpoison_memory()
On Thu, Nov 4, 2021 at 10:52 PM Naoya Horiguchi
<naoya.horiguchi@...ux.dev> wrote:
>
> From: Naoya Horiguchi <naoya.horiguchi@....com>
>
> After recent soft-offline rework, error pages can be taken off from
> buddy allocator, but the existing unpoison_memory() does not properly
> undo the operation. Moreover, due to the recent change on
> __get_hwpoison_page(), get_page_unless_zero() is hardly called for
> hwpoisoned pages. So __get_hwpoison_page() highly likely returns -EBUSY
> (meaning to fail to grab page refcount) and unpoison just clears
> PG_hwpoison without releasing a refcount. That does not lead to a
> critical issue like kernel panic, but unpoisoned pages never get back to
> buddy (leaked permanently), which is not good.
>
> To (partially) fix this, we need to identify "taken off" pages from
> other types of hwpoisoned pages. We can't use refcount or page flags
> for this purpose, so a pseudo flag is defined by hacking ->private
> field. Someone might think that put_page() is enough to cancel
> taken-off pages, but the normal free path contains some operations not
> suitable for the current purpose, and can fire VM_BUG_ON().
>
> Note that unpoison_memory() is now supposed to be cancel hwpoison events
> injected only by madvise() or /sys/devices/system/memory/{hard,soft}_offline_page,
> not by MCE injection, so please don't try to use unpoison when testing
> with MCE injection.
>
> Signed-off-by: Naoya Horiguchi <naoya.horiguchi@....com>
> ---
> ChangeLog v3:
> - fix description
> - add PageTable check in unpoison_memory()
> - fix return value of clear_page_hwpoison()
> - pass page instead head to PageHWPoisonTakenOff check.
> - rename take_page_back_buddy() with put_page_back_buddy()
>
> ChangeLog v2:
> - unpoison_memory() returns as commented
> - explicitly avoids unpoisoning slab pages
> - separates internal pinning function into __get_unpoison_page()
> ---
> include/linux/mm.h | 1 +
> include/linux/page-flags.h | 4 ++
> mm/memory-failure.c | 107 ++++++++++++++++++++++++++++++-------
> mm/page_alloc.c | 23 ++++++++
> 4 files changed, 116 insertions(+), 19 deletions(-)
>
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 7941bca871dc..8bbb7205ef9f 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -3220,6 +3220,7 @@ enum mf_flags {
> MF_ACTION_REQUIRED = 1 << 1,
> MF_MUST_KILL = 1 << 2,
> MF_SOFT_OFFLINE = 1 << 3,
> + MF_UNPOISON = 1 << 4,
> };
> extern int memory_failure(unsigned long pfn, int flags);
> extern void memory_failure_queue(unsigned long pfn, int flags);
> diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
> index 52ec4b5e5615..ccfe083152c4 100644
> --- a/include/linux/page-flags.h
> +++ b/include/linux/page-flags.h
> @@ -522,7 +522,11 @@ PAGEFLAG_FALSE(Uncached, uncached)
> PAGEFLAG(HWPoison, hwpoison, PF_ANY)
> TESTSCFLAG(HWPoison, hwpoison, PF_ANY)
> #define __PG_HWPOISON (1UL << PG_hwpoison)
> +#define MAGIC_HWPOISON 0x4857504f49534f4e
> +extern void SetPageHWPoisonTakenOff(struct page *page);
> +extern void ClearPageHWPoisonTakenOff(struct page *page);
> extern bool take_page_off_buddy(struct page *page);
> +extern bool put_page_back_buddy(struct page *page);
> #else
> PAGEFLAG_FALSE(HWPoison, hwpoison)
> #define __PG_HWPOISON 0
> diff --git a/mm/memory-failure.c b/mm/memory-failure.c
> index 722036539b44..f406e85eb733 100644
> --- a/mm/memory-failure.c
> +++ b/mm/memory-failure.c
> @@ -1160,6 +1160,22 @@ static int page_action(struct page_state *ps, struct page *p,
> return (result == MF_RECOVERED || result == MF_DELAYED) ? 0 : -EBUSY;
> }
>
> +static inline bool PageHWPoisonTakenOff(struct page *page)
> +{
> + return PageHWPoison(page) && page_private(page) == MAGIC_HWPOISON;
> +}
> +
> +void SetPageHWPoisonTakenOff(struct page *page)
> +{
> + set_page_private(page, MAGIC_HWPOISON);
> +}
> +
> +void ClearPageHWPoisonTakenOff(struct page *page)
> +{
> + if (PageHWPoison(page))
> + set_page_private(page, 0);
> +}
> +
> /*
> * Return true if a page type of a given page is supported by hwpoison
> * mechanism (while handling could fail), otherwise false. This function
> @@ -1262,6 +1278,27 @@ static int get_any_page(struct page *p, unsigned long flags)
> return ret;
> }
>
> +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);
> + if (hugetlb)
> + return ret;
> +
> + /*
> + * PageHWPoisonTakenOff pages are not only marked as PG_hwpoison,
> + * but also isolated from buddy freelist, so need to identify the
> + * state and have to cancel both operations to unpoison.
> + */
> + if (PageHWPoisonTakenOff(page))
> + return -EHWPOISON;
> +
> + return get_page_unless_zero(page) ? 1 : 0;
> +}
> +
> /**
> * get_hwpoison_page() - Get refcount for memory error handling
> * @p: Raw error page (hit by memory error)
> @@ -1278,18 +1315,26 @@ static int get_any_page(struct page *p, unsigned long flags)
> * extra care for the error page's state (as done in __get_hwpoison_page()),
> * and has some retry logic in get_any_page().
> *
> + * When called from unpoison_memory(), the caller should already ensure that
> + * the given page has PG_hwpoison. So it's never reused for other page
> + * allocations, and __get_unpoison_page() never races with them.
> + *
> * Return: 0 on failure,
> * 1 on success for in-use pages in a well-defined state,
> * -EIO for pages on which we can not handle memory errors,
> * -EBUSY when get_hwpoison_page() has raced with page lifecycle
> - * operations like allocation and free.
> + * operations like allocation and free,
> + * -EHWPOISON when the page is hwpoisoned and taken off from buddy.
> */
> static int get_hwpoison_page(struct page *p, unsigned long flags)
> {
> int ret;
>
> zone_pcp_disable(page_zone(p));
> - ret = get_any_page(p, flags);
> + if (flags & MF_UNPOISON)
> + ret = __get_unpoison_page(p);
> + else
> + ret = get_any_page(p, flags);
> zone_pcp_enable(page_zone(p));
>
> return ret;
> @@ -1942,6 +1987,26 @@ core_initcall(memory_failure_init);
> pr_info(fmt, pfn); \
> })
>
> +static inline int clear_page_hwpoison(struct ratelimit_state *rs, struct page *p)
> +{
> + if (TestClearPageHWPoison(p)) {
> + unpoison_pr_info("Unpoison: Software-unpoisoned page %#lx\n",
> + page_to_pfn(p), rs);
> + num_poisoned_pages_dec();
> + return 1;
> + }
> + return 0;
> +}
> +
> +static inline int unpoison_taken_off_page(struct ratelimit_state *rs,
> + struct page *p)
> +{
> + if (put_page_back_buddy(p) && clear_page_hwpoison(rs, p))
It seems there might be race condition between free and allocation to
kick the page out of buddy before the hwpoisoned flag is cleared IIUC?
CPU A CPU B
Free: Allocation:
acquire zone lock
put back to buddy
release zone lock
acquire zone lock
try to allocate this page
if it is hwpoisoned then reset
PageBuddy (not buddy page anymore)
release zone lock
Did I miss something?
> + return 0;
> + else
> + return -EBUSY;
> +}
> +
> /**
> * unpoison_memory - Unpoison a previously poisoned page
> * @pfn: Page number of the to be unpoisoned page
> @@ -1958,9 +2023,7 @@ int unpoison_memory(unsigned long pfn)
> {
> struct page *page;
> struct page *p;
> - int freeit = 0;
> - int ret = 0;
> - unsigned long flags = 0;
> + int ret = -EBUSY;
> static DEFINE_RATELIMIT_STATE(unpoison_rs, DEFAULT_RATELIMIT_INTERVAL,
> DEFAULT_RATELIMIT_BURST);
>
> @@ -1996,24 +2059,30 @@ int unpoison_memory(unsigned long pfn)
> goto unlock_mutex;
> }
>
> - if (!get_hwpoison_page(p, flags)) {
> - if (TestClearPageHWPoison(p))
> - num_poisoned_pages_dec();
> - unpoison_pr_info("Unpoison: Software-unpoisoned free page %#lx\n",
> - pfn, &unpoison_rs);
> + if (PageSlab(page) || PageTable(page))
> goto unlock_mutex;
> - }
>
> - if (TestClearPageHWPoison(page)) {
> - unpoison_pr_info("Unpoison: Software-unpoisoned page %#lx\n",
> - pfn, &unpoison_rs);
> - num_poisoned_pages_dec();
> - freeit = 1;
> - }
> + ret = get_hwpoison_page(p, MF_UNPOISON);
> + if (!ret) {
> + if (clear_page_hwpoison(&unpoison_rs, page))
> + ret = 0;
> + else
> + ret = -EBUSY;
> + } else if (ret < 0) {
> + if (ret == -EHWPOISON) {
> + ret = unpoison_taken_off_page(&unpoison_rs, p);
> + } else
> + unpoison_pr_info("Unpoison: failed to grab page %#lx\n",
> + pfn, &unpoison_rs);
> + } else {
> + int freeit = clear_page_hwpoison(&unpoison_rs, p);
>
> - put_page(page);
> - if (freeit && !(pfn == my_zero_pfn(0) && page_count(p) == 1))
> put_page(page);
> + if (freeit && !(pfn == my_zero_pfn(0) && page_count(p) == 1)) {
> + put_page(page);
> + ret = 0;
> + }
> + }
>
> unlock_mutex:
> mutex_unlock(&mf_mutex);
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index c5952749ad40..3a2e23e6c769 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -9448,6 +9448,7 @@ bool take_page_off_buddy(struct page *page)
> del_page_from_free_list(page_head, zone, page_order);
> break_down_buddy_pages(zone, page_head, page, 0,
> page_order, migratetype);
> + SetPageHWPoisonTakenOff(page);
> if (!is_migrate_isolate(migratetype))
> __mod_zone_freepage_state(zone, -1, migratetype);
> ret = true;
> @@ -9459,4 +9460,26 @@ bool take_page_off_buddy(struct page *page)
> spin_unlock_irqrestore(&zone->lock, flags);
> return ret;
> }
> +
> +/*
> + * Cancel takeoff done by take_page_off_buddy().
> + */
> +bool put_page_back_buddy(struct page *page)
> +{
> + struct zone *zone = page_zone(page);
> + unsigned long pfn = page_to_pfn(page);
> + unsigned long flags;
> + int migratetype = get_pfnblock_migratetype(page, pfn);
> + bool ret = false;
> +
> + spin_lock_irqsave(&zone->lock, flags);
> + if (put_page_testzero(page)) {
> + ClearPageHWPoisonTakenOff(page);
> + __free_one_page(page, pfn, zone, 0, migratetype, FPI_NONE);
> + ret = true;
> + }
> + spin_unlock_irqrestore(&zone->lock, flags);
> +
> + return ret;
> +}
> #endif
> --
> 2.25.1
>
>
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