[patch 03/18] mm: hugetlb: fix a race between isolating and freeing page

From: Muchun Song <redacted>
Subject: mm: hugetlb: fix a race between isolating and freeing page

There is a race between isolate_huge_page() and __free_huge_page().

CPU0:                                       CPU1:

if (PageHuge(page))
                                            put_page(page)
                                              __free_huge_page(page)
                                                  spin_lock(&hugetlb_lock)
                                                  update_and_free_page(page)
                                                    set_compound_page_dtor(page,
                                                      NULL_COMPOUND_DTOR)
                                                  spin_unlock(&hugetlb_lock)
  isolate_huge_page(page)
    // trigger BUG_ON
    VM_BUG_ON_PAGE(!PageHead(page), page)
    spin_lock(&hugetlb_lock)
    page_huge_active(page)
      // trigger BUG_ON
      VM_BUG_ON_PAGE(!PageHuge(page), page)
    spin_unlock(&hugetlb_lock)

When we isolate a HugeTLB page on CPU0. Meanwhile, we free it to the
buddy allocator on CPU1. Then, we can trigger a BUG_ON on CPU0. Because
it is already freed to the buddy allocator.

Link: https://lkml.kernel.org/r/20210115124942.46403-5-songmuchun@bytedance.com
Fixes: c8721bbbdd36 ("mm: memory-hotplug: enable memory hotplug to handle hugepage")
Signed-off-by: Muchun Song <redacted>
Reviewed-by: Mike Kravetz <redacted>
Acked-by: Michal Hocko <mhocko@suse.com>
Reviewed-by: Oscar Salvador <osalvador@suse.de>
Cc: David Hildenbrand <redacted>
Cc: Yang Shi <redacted>
Cc: <redacted>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/hugetlb.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

--- a/mm/hugetlb.c~mm-hugetlb-fix-a-race-between-isolating-and-freeing-page
+++ a/mm/hugetlb.c

@@ -5594,9 +5594,9 @@ bool isolate_huge_page(struct page *page
 {
 	bool ret = true;
 
-	VM_BUG_ON_PAGE(!PageHead(page), page);
 	spin_lock(&hugetlb_lock);
-	if (!page_huge_active(page) || !get_page_unless_zero(page)) {
+	if (!PageHeadHuge(page) || !page_huge_active(page) ||
+	    !get_page_unless_zero(page)) {
 		ret = false;
 		goto unlock;
 	}

_