[PATCH v4 5/6] mm: hugetlb: fix a race between isolating and freeing page

[Muchun Song]

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.

Fixes: c8721bbbdd36 ("mm: memory-hotplug: enable memory hotplug to handle 
hugepage")
Signed-off-by: Muchun Song <songmuc...@bytedance.com>
Reviewed-by: Mike Kravetz <mike.krav...@oracle.com>
Acked-by: Michal Hocko <mho...@suse.com>
Cc: sta...@vger.kernel.org
---
 mm/hugetlb.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 898e4ea43e13..a7ed22811672 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -5575,9 +5575,9 @@ bool isolate_huge_page(struct page *page, struct 
list_head *list)
 {
        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;
        }
-- 
2.11.0