Date:   Mon, 11 Jul 2022 11:26:34 +0800
From:   Miaohe Lin <linmiaohe@...wei.com>
To:     Naoya Horiguchi <naoya.horiguchi@...ux.dev>, <linux-mm@...ck.org>
CC:     Andrew Morton <akpm@...ux-foundation.org>,
        David Hildenbrand <david@...hat.com>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Liu Shixin <liushixin2@...wei.com>,
        Yang Shi <shy828301@...il.com>,
        Oscar Salvador <osalvador@...e.de>,
        Muchun Song <songmuchun@...edance.com>,
        Naoya Horiguchi <naoya.horiguchi@....com>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [mm-unstable PATCH v5 3/8] mm, hwpoison, hugetlb: support saving
 mechanism of raw error pages

On 2022/7/8 13:36, Naoya Horiguchi wrote:
> From: Naoya Horiguchi <naoya.horiguchi@....com>
> 
> When handling memory error on a hugetlb page, the error handler tries to
> dissolve and turn it into 4kB pages.  If it's successfully dissolved,
> PageHWPoison flag is moved to the raw error page, so that's all right.
> However, dissolve sometimes fails, then the error page is left as
> hwpoisoned hugepage. It's useful if we can retry to dissolve it to save
> healthy pages, but that's not possible now because the information about
> where the raw error pages is lost.
> 
> Use the private field of a few tail pages to keep that information.  The
> code path of shrinking hugepage pool uses this info to try delayed dissolve.
> In order to remember multiple errors in a hugepage, a singly-linked list
> originated from SUBPAGE_INDEX_HWPOISON-th tail page is constructed.  Only
> simple operations (adding an entry or clearing all) are required and the
> list is assumed not to be very long, so this simple data structure should
> be enough.
> 
> If we failed to save raw error info, the hwpoison hugepage has errors on
> unknown subpage, then this new saving mechanism does not work any more,
> so disable saving new raw error info and freeing hwpoison hugepages.
> 
> Signed-off-by: Naoya Horiguchi <naoya.horiguchi@....com>
> Reported-by: kernel test robot <lkp@...el.com>
> ---
> v4 -> v5:
> - fixed build error (reported by kernel test robot).
> - do not try to undo remove_hugetlb_page() when HPageRawHwpUnreliable is true,
> - check HPageRawHwpUnreliable() before hugetlb_vmemmap_restore(),
> - call num_poisoned_pages_inc() in hugetlb_set_page_hwpoison() when kalloc
>   succeeds,
> - remove "inline" in the definition of hugetlb_clear_page_hwpoison().
> 
> v3 -> v4:
> - resolve conflict with "mm: hugetlb_vmemmap: improve hugetlb_vmemmap
>   code readability", use hugetlb_vmemmap_restore() instead of
>   hugetlb_vmemmap_alloc().
> 
> v2 -> v3:
> - remove duplicate "return ret" lines,
> - use GFP_ATOMIC instead of GFP_KERNEL,
> - introduce HPageRawHwpUnreliable pseudo flag (suggested by Muchun),
> - hugetlb_clear_page_hwpoison removes raw_hwp_page list even if
>   HPageRawHwpUnreliable is true, (by Miaohe)
> 
> v1 -> v2:
> - support hwpoison hugepage with multiple errors,
> - moved the new interface functions to mm/memory-failure.c,
> - define additional subpage index SUBPAGE_INDEX_HWPOISON_UNRELIABLE,
> - stop freeing/dissolving hwpoison hugepages with unreliable raw error info,
> - drop hugetlb_clear_page_hwpoison() in dissolve_free_huge_page() because
>   that's done in update_and_free_page(),
> - move setting/clearing PG_hwpoison flag to the new interfaces,
> - checking already hwpoisoned or not on a subpage basis.
> 
> ChangeLog since previous post on 4/27:
> - fixed typo in patch description (by Miaohe)
> - fixed config value in #ifdef statement (by Miaohe)
> - added sentences about "multiple hwpoison pages" scenario in patch
>   description
> ---
>  include/linux/hugetlb.h | 18 +++++++++-
>  mm/hugetlb.c            | 32 ++++++++++++-----
>  mm/memory-failure.c     | 79 +++++++++++++++++++++++++++++++++++++++--
>  3 files changed, 116 insertions(+), 13 deletions(-)
> 
> diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
> index 6d0620edf0a6..6fd128b80d57 100644
> --- a/include/linux/hugetlb.h
> +++ b/include/linux/hugetlb.h
> @@ -42,6 +42,9 @@ enum {
>  	SUBPAGE_INDEX_CGROUP,		/* reuse page->private */
>  	SUBPAGE_INDEX_CGROUP_RSVD,	/* reuse page->private */
>  	__MAX_CGROUP_SUBPAGE_INDEX = SUBPAGE_INDEX_CGROUP_RSVD,
> +#endif
> +#ifdef CONFIG_MEMORY_FAILURE
> +	SUBPAGE_INDEX_HWPOISON,
>  #endif
>  	__NR_USED_SUBPAGE,
>  };
> @@ -551,7 +554,7 @@ generic_hugetlb_get_unmapped_area(struct file *file, unsigned long addr,
>   *	Synchronization:  Initially set after new page allocation with no
>   *	locking.  When examined and modified during migration processing
>   *	(isolate, migrate, putback) the hugetlb_lock is held.
> - * HPG_temporary - - Set on a page that is temporarily allocated from the buddy
> + * HPG_temporary - Set on a page that is temporarily allocated from the buddy
>   *	allocator.  Typically used for migration target pages when no pages
>   *	are available in the pool.  The hugetlb free page path will
>   *	immediately free pages with this flag set to the buddy allocator.
> @@ -561,6 +564,8 @@ generic_hugetlb_get_unmapped_area(struct file *file, unsigned long addr,
>   * HPG_freed - Set when page is on the free lists.
>   *	Synchronization: hugetlb_lock held for examination and modification.
>   * HPG_vmemmap_optimized - Set when the vmemmap pages of the page are freed.
> + * HPG_raw_hwp_unreliable - Set when the hugetlb page has a hwpoison sub-page
> + *     that is not tracked by raw_hwp_page list.
>   */
>  enum hugetlb_page_flags {
>  	HPG_restore_reserve = 0,
> @@ -568,6 +573,7 @@ enum hugetlb_page_flags {
>  	HPG_temporary,
>  	HPG_freed,
>  	HPG_vmemmap_optimized,
> +	HPG_raw_hwp_unreliable,
>  	__NR_HPAGEFLAGS,
>  };
>  
> @@ -614,6 +620,7 @@ HPAGEFLAG(Migratable, migratable)
>  HPAGEFLAG(Temporary, temporary)
>  HPAGEFLAG(Freed, freed)
>  HPAGEFLAG(VmemmapOptimized, vmemmap_optimized)
> +HPAGEFLAG(RawHwpUnreliable, raw_hwp_unreliable)
>  
>  #ifdef CONFIG_HUGETLB_PAGE
>  
> @@ -796,6 +803,15 @@ extern int dissolve_free_huge_page(struct page *page);
>  extern int dissolve_free_huge_pages(unsigned long start_pfn,
>  				    unsigned long end_pfn);
>  
> +#ifdef CONFIG_MEMORY_FAILURE
> +extern int hugetlb_clear_page_hwpoison(struct page *hpage);
> +#else
> +static inline int hugetlb_clear_page_hwpoison(struct page *hpage)
> +{
> +	return 0;
> +}
> +#endif
> +
>  #ifdef CONFIG_ARCH_ENABLE_HUGEPAGE_MIGRATION
>  #ifndef arch_hugetlb_migration_supported
>  static inline bool arch_hugetlb_migration_supported(struct hstate *h)
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index 77119d93a0f9..3956494cc5fb 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -1442,6 +1442,15 @@ static void __remove_hugetlb_page(struct hstate *h, struct page *page,
>  		h->surplus_huge_pages_node[nid]--;
>  	}
>  
> +	/*
> +	 * This leaves HPageRawHwpUnreliable pages as leaked hugepages, not
> +	 * as leaked generic-compound pages.  Otherwise page_mapped() or
> +	 * folio_mapped() gets slow because for-loop for each subpage is
> +	 * called.
> +	 */
> +	if (HPageRawHwpUnreliable(page))
> +		return;
> +

This patch looks good to me with below several possible problems:

Should "nr_huge_pages" and "nr_huge_pages_node" be adjusted too? If it's called from dissolve_free_huge_page
and hugetlb_vmemmap_restore fails, add_hugetlb_page will be called:

add_hugetlb_page:
	...
	h->nr_huge_pages++;
	h->nr_huge_pages_node[nid]++;
	   ^^^^^^^^1. the "nr_huge_pages" and "nr_huge_pages_node" might be incorrect?
	...
	zeroed = put_page_testzero(page);
		 ^^^^^^^^2. VM_BUG_ON_PAGE(page_ref_count(page) == 0, page); will be triggered?

Or am I miss something?

Thanks!

>  	/*
>  	 * Very subtle
>  	 *
> @@ -1535,6 +1544,13 @@ static void __update_and_free_page(struct hstate *h, struct page *page)
>  	if (hstate_is_gigantic(h) && !gigantic_page_runtime_supported())
>  		return;
>  
> +	/*
> +	 * If we don't know which subpages are hwpoisoned, we can't free
> +	 * the hugepage, so it's leaked intentionally.
> +	 */
> +	if (HPageRawHwpUnreliable(page))
> +		return;
> +
>  	if (hugetlb_vmemmap_restore(h, page)) {
>  		spin_lock_irq(&hugetlb_lock);
>  		/*
> @@ -1547,6 +1563,13 @@ static void __update_and_free_page(struct hstate *h, struct page *page)
>  		return;
>  	}
>  
> +	/*
> +	 * Move PageHWPoison flag from head page to the raw error pages,
> +	 * which makes any healthy subpages reusable.
> +	 */
> +	if (unlikely(PageHWPoison(page)))
> +		hugetlb_clear_page_hwpoison(page);
> +
>  	for (i = 0; i < pages_per_huge_page(h);
>  	     i++, subpage = mem_map_next(subpage, page, i)) {
>  		subpage->flags &= ~(1 << PG_locked | 1 << PG_error |
> @@ -2109,15 +2132,6 @@ int dissolve_free_huge_page(struct page *page)
>  		 */
>  		rc = hugetlb_vmemmap_restore(h, head);
>  		if (!rc) {
> -			/*
> -			 * Move PageHWPoison flag from head page to the raw
> -			 * error page, which makes any subpages rather than
> -			 * the error page reusable.
> -			 */
> -			if (PageHWPoison(head) && page != head) {
> -				SetPageHWPoison(page);
> -				ClearPageHWPoison(head);
> -			}
>  			update_and_free_page(h, head, false);
>  		} else {
>  			spin_lock_irq(&hugetlb_lock);
> diff --git a/mm/memory-failure.c b/mm/memory-failure.c
> index c9931c676335..6833c5e4b410 100644
> --- a/mm/memory-failure.c
> +++ b/mm/memory-failure.c
> @@ -1664,6 +1664,80 @@ int mf_dax_kill_procs(struct address_space *mapping, pgoff_t index,
>  EXPORT_SYMBOL_GPL(mf_dax_kill_procs);
>  #endif /* CONFIG_FS_DAX */
>  
> +#ifdef CONFIG_HUGETLB_PAGE
> +/*
> + * Struct raw_hwp_page represents information about "raw error page",
> + * constructing singly linked list originated from ->private field of
> + * SUBPAGE_INDEX_HWPOISON-th tail page.
> + */
> +struct raw_hwp_page {
> +	struct llist_node node;
> +	struct page *page;
> +};
> +
> +static inline struct llist_head *raw_hwp_list_head(struct page *hpage)
> +{
> +	return (struct llist_head *)&page_private(hpage + SUBPAGE_INDEX_HWPOISON);
> +}
> +
> +static int hugetlb_set_page_hwpoison(struct page *hpage, struct page *page)
> +{
> +	struct llist_head *head;
> +	struct raw_hwp_page *raw_hwp;
> +	struct llist_node *t, *tnode;
> +	int ret = TestSetPageHWPoison(hpage) ? -EHWPOISON : 0;
> +
> +	/*
> +	 * Once the hwpoison hugepage has lost reliable raw error info,
> +	 * there is little meaning to keep additional error info precisely,
> +	 * so skip to add additional raw error info.
> +	 */
> +	if (HPageRawHwpUnreliable(hpage))
> +		return -EHWPOISON;
> +	head = raw_hwp_list_head(hpage);
> +	llist_for_each_safe(tnode, t, head->first) {
> +		struct raw_hwp_page *p = container_of(tnode, struct raw_hwp_page, node);
> +
> +		if (p->page == page)
> +			return -EHWPOISON;
> +	}
> +
> +	raw_hwp = kmalloc(sizeof(struct raw_hwp_page), GFP_ATOMIC);
> +	if (raw_hwp) {
> +		raw_hwp->page = page;
> +		llist_add(&raw_hwp->node, head);
> +		/* the first error event will be counted in action_result(). */
> +		if (ret)
> +			num_poisoned_pages_inc();
> +	} else {
> +		/*
> +		 * Failed to save raw error info.  We no longer trace all
> +		 * hwpoisoned subpages, and we need refuse to free/dissolve
> +		 * this hwpoisoned hugepage.
> +		 */
> +		SetHPageRawHwpUnreliable(hpage);
> +	}
> +	return ret;
> +}
> +
> +int hugetlb_clear_page_hwpoison(struct page *hpage)
> +{
> +	struct llist_head *head;
> +	struct llist_node *t, *tnode;
> +
> +	if (!HPageRawHwpUnreliable(hpage))
> +		ClearPageHWPoison(hpage);
> +	head = raw_hwp_list_head(hpage);
> +	llist_for_each_safe(tnode, t, head->first) {
> +		struct raw_hwp_page *p = container_of(tnode, struct raw_hwp_page, node);
> +
> +		SetPageHWPoison(p->page);
> +		kfree(p);
> +	}
> +	llist_del_all(head);
> +	return 0;
> +}
> +
>  /*
>   * Called from hugetlb code with hugetlb_lock held.
>   *
> @@ -1698,7 +1772,7 @@ int __get_huge_page_for_hwpoison(unsigned long pfn, int flags)
>  		goto out;
>  	}
>  
> -	if (TestSetPageHWPoison(head)) {
> +	if (hugetlb_set_page_hwpoison(head, page)) {
>  		ret = -EHWPOISON;
>  		goto out;
>  	}
> @@ -1710,7 +1784,6 @@ int __get_huge_page_for_hwpoison(unsigned long pfn, int flags)
>  	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.
> @@ -1751,7 +1824,7 @@ static int try_memory_failure_hugetlb(unsigned long pfn, int flags, int *hugetlb
>  	lock_page(head);
>  
>  	if (hwpoison_filter(p)) {
> -		ClearPageHWPoison(head);
> +		hugetlb_clear_page_hwpoison(head);
>  		res = -EOPNOTSUPP;
>  		goto out;
>  	}
> 

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