Re: [PATCH v5 1/2] mm,hwpoison: fix race with hugetlb page allocation

[HORIGUCHI NAOYA(堀口 直也)]

On Tue, May 25, 2021 at 09:36:05AM +0200, Oscar Salvador wrote:
> On Thu, May 20, 2021 at 07:17:17AM +0000, HORIGUCHI NAOYA(堀口 直也) wrote:
> > So I think of inserting the check to comply with the assumption of
> > get_hwpoison_huge_page() like below:
> > 
> >         ret = get_hwpoison_huge_page(head, &hugetlb);
> >         if (hugetlb)
> >                 return ret;
> > 
> >         if (!PageLRU(head) && !__PageMovable(head))
> >                 return 0;
> > 
> >         if (PageTransHuge(head)) {
> >                 ...
> >         }
> > 
> >         if (get_page_unless_zero(head)) {
> >                 ...
> >         }
> > 
> >         return 0;
> 
> Hi Naoya,
> 
> would you mind posting a complete draft of what it would look like?
> I am having a hard time picturing it.

OK, here's the current draft.

Thanks,
Naoya Horiguchi

---
From: Naoya Horiguchi <naoya.horiguchi@xxxxxxx>
Date: Tue, 18 May 2021 23:49:18 +0900
Subject: [PATCH] mm,hwpoison: fix race with hugetlb page allocation

When hugetlb page fault (under overcommitting 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 the page refcount before taking an
additional one for memory error handling, which is wrong because there's
a time window where compound pages have non-zero refcount during
initialization.  So make __get_hwpoison_page() check page status a bit
more for hugetlb pages.

Fixes: ead07f6a867b ("mm/memory-failure: introduce get_hwpoison_page() for consistent refcount handling")
Signed-off-by: Naoya Horiguchi <naoya.horiguchi@xxxxxxx>
Reported-by: Muchun Song <songmuchun@xxxxxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx # 5.12+
---
 include/linux/hugetlb.h |  6 ++++++
 mm/hugetlb.c            | 15 +++++++++++++++
 mm/memory-failure.c     | 11 ++++++++++-
 3 files changed, 31 insertions(+), 1 deletion(-)

diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
index b92f25ccef58..790ae618548d 100644
--- a/include/linux/hugetlb.h
+++ b/include/linux/hugetlb.h
@@ -149,6 +149,7 @@ bool hugetlb_reserve_pages(struct inode *inode, long from, long to,
 long hugetlb_unreserve_pages(struct inode *inode, long start, long end,
 						long freed);
 bool isolate_huge_page(struct page *page, struct list_head *list);
+int get_hwpoison_huge_page(struct page *page, bool *hugetlb);
 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);
@@ -339,6 +340,11 @@ static inline bool isolate_huge_page(struct page *page, struct list_head *list)
 	return false;
 }
 
+static inline int get_hwpoison_huge_page(struct page *page, bool *hugetlb)
+{
+	return 0;
+}
+
 static inline void putback_active_hugepage(struct page *page)
 {
 }
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 95918f410c0f..f138bae3e302 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -5847,6 +5847,21 @@ bool isolate_huge_page(struct page *page, struct list_head *list)
 	return ret;
 }
 
+int get_hwpoison_huge_page(struct page *page, bool *hugetlb)
+{
+	int ret = 0;
+
+	*hugetlb = false;
+	spin_lock_irq(&hugetlb_lock);
+	if (PageHeadHuge(page)) {
+		*hugetlb = true;
+		if (HPageFreed(page) || HPageMigratable(page))
+			ret = get_page_unless_zero(page);
+	}
+	spin_unlock_irq(&hugetlb_lock);
+	return ret;
+}
+
 void putback_active_hugepage(struct page *page)
 {
 	spin_lock_irq(&hugetlb_lock);
diff --git a/mm/memory-failure.c b/mm/memory-failure.c
index 85ad98c00fd9..4c264c4090d7 100644
--- a/mm/memory-failure.c
+++ b/mm/memory-failure.c
@@ -959,8 +959,17 @@ static int page_action(struct page_state *ps, struct page *p,
 static int __get_hwpoison_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;
+
+	if (!PageLRU(head) && !__PageMovable(head))
+		return 0;
 
-	if (!PageHuge(head) && PageTransHuge(head)) {
+	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.
-- 
2.25.1