[PATCH 5.12 166/178] mm,hwpoison: fix race with hugetlb page allocation

Greg Kroah-Hartman
2021-06-21T16:52:35Z

From: Naoya Horiguchi <naoya.horiguchi@nec.com>

commit 25182f05ffed0b45602438693e4eed5d7f3ebadd upstream.

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 not enough because
there's a time window where compound pages have non-zero refcount during
hugetlb page initialization.

So make __get_hwpoison_page() check page status a bit more for hugetlb
pages with get_hwpoison_huge_page(). Checking hugetlb-specific flags
under hugetlb_lock makes sure that the hugetlb page is not transitive.
It's notable that another new function, HWPoisonHandlable(), is helpful
to prevent a race against other transitive page states (like a generic
compound page just before PageHuge becomes true).

Link: https://lkml.kernel.org/r/20210603233632.2964832-2-nao.horiguchi@gmail.com
Fixes: ead07f6a867b ("mm/memory-failure: introduce get_hwpoison_page() for consistent refcount handling")
Signed-off-by: Naoya Horiguchi <naoya.horiguchi@nec.com>
Reported-by: Muchun Song <songmuchun@bytedance.com>
Acked-by: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Tony Luck <tony.luck@intel.com>
Cc: <stable@vger.kernel.org> [5.12+]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
include/linux/hugetlb.h | 6 ++++++
mm/hugetlb.c | 15 +++++++++++++++
mm/memory-failure.c | 29 +++++++++++++++++++++++++++--
3 files changed, 48 insertions(+), 2 deletions(-)

--- a/include/linux/hugetlb.h
+++ b/include/linux/hugetlb.h
@@ -145,6 +145,7 @@ bool hugetlb_reserve_pages(struct inode
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);
@@ -330,6 +331,11 @@ static inline bool isolate_huge_page(str
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)
{
}
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -5664,6 +5664,21 @@ unlock:
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(&hugetlb_lock);
--- a/mm/memory-failure.c
+++ b/mm/memory-failure.c
@@ -949,6 +949,17 @@ static int page_action(struct page_state
return (result == MF_RECOVERED || result == MF_DELAYED) ? 0 : -EBUSY;
}

+/*
+ * Return true if a page type of a given page is supported by hwpoison
+ * mechanism (while handling could fail), otherwise false. This function
+ * does not return true for hugetlb or device memory pages, so it's assumed
+ * to be called only in the context where we never have such pages.
+ */
+static inline bool HWPoisonHandlable(struct page *page)
+{
+ return PageLRU(page) || __PageMovable(page);
+}
+
/**
* __get_hwpoison_page() - Get refcount for memory error handling:
* @page: raw error page (hit by memory error)
@@ -959,8 +970,22 @@ static int page_action(struct page_state
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;
+
+ /*
+ * This check prevents from calling get_hwpoison_unless_zero()
+ * for any unsupported type of page in order to reduce the risk of
+ * unexpected races caused by taking a page refcount.
+ */
+ if (!HWPoisonHandlable(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.
@@ -1017,7 +1042,7 @@ try_again:
ret = -EIO;
}
} else {
- if (PageHuge(p) || PageLRU(p) || __PageMovable(p)) {
+ if (PageHuge(p) || HWPoisonHandlable(p)) {
ret = 1;
} else {
/*