The patch titled
Subject: mm: hugetlb: fix a race between freeing and dissolving the page
has been added to the -mm tree. Its filename is
mm-hugetlb-fix-a-race-between-freeing-and-dissolving-the-page.patch
This patch should soon appear at
https://ozlabs.org/~akpm/mmots/broken-out/mm-hugetlb-fix-a-race-between-freeing-and-dissolving-the-page.patch
and later at
https://ozlabs.org/~akpm/mmotm/broken-out/mm-hugetlb-fix-a-race-between-freeing-and-dissolving-the-page.patch
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------------------------------------------------------
From: Muchun Song <songmuchun@xxxxxxxxxxxxx>
Subject: mm: hugetlb: fix a race between freeing and dissolving the page
There is a race condition between __free_huge_page()
and dissolve_free_huge_page().
CPU0: CPU1:
// page_count(page) == 1
put_page(page)
__free_huge_page(page)
dissolve_free_huge_page(page)
spin_lock(&hugetlb_lock)
// PageHuge(page) && !page_count(page)
update_and_free_page(page)
// page is freed to the buddy
spin_unlock(&hugetlb_lock)
spin_lock(&hugetlb_lock)
clear_page_huge_active(page)
enqueue_huge_page(page)
// It is wrong, the page is already freed
spin_unlock(&hugetlb_lock)
The race windows is between put_page() and dissolve_free_huge_page().
We should make sure that the page is already on the free list
when it is dissolved.
Link: https://lkml.kernel.org/r/20210110124017.86750-4-songmuchun@xxxxxxxxxxxxx
Fixes: c8721bbbdd36 ("mm: memory-hotplug: enable memory hotplug to handle hugepage")
Signed-off-by: Muchun Song <songmuchun@xxxxxxxxxxxxx>
Cc: Andi Kleen <ak@xxxxxxxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxx>
Cc: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
Cc: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/hugetlb.c | 26 ++++++++++++++++++++++++++
1 file changed, 26 insertions(+)
--- a/mm/hugetlb.c~mm-hugetlb-fix-a-race-between-freeing-and-dissolving-the-page
+++ a/mm/hugetlb.c
@@ -79,6 +79,21 @@ DEFINE_SPINLOCK(hugetlb_lock);
static int num_fault_mutexes;
struct mutex *hugetlb_fault_mutex_table ____cacheline_aligned_in_smp;
+static inline bool PageHugeFreed(struct page *head)
+{
+ return page_private(head + 4) == -1UL;
+}
+
+static inline void SetPageHugeFreed(struct page *head)
+{
+ set_page_private(head + 4, -1UL);
+}
+
+static inline void ClearPageHugeFreed(struct page *head)
+{
+ set_page_private(head + 4, 0);
+}
+
/* Forward declaration */
static int hugetlb_acct_memory(struct hstate *h, long delta);
@@ -1028,6 +1043,7 @@ static void enqueue_huge_page(struct hst
list_move(&page->lru, &h->hugepage_freelists[nid]);
h->free_huge_pages++;
h->free_huge_pages_node[nid]++;
+ SetPageHugeFreed(page);
}
static struct page *dequeue_huge_page_node_exact(struct hstate *h, int nid)
@@ -1044,6 +1060,7 @@ static struct page *dequeue_huge_page_no
list_move(&page->lru, &h->hugepage_activelist);
set_page_refcounted(page);
+ ClearPageHugeFreed(page);
h->free_huge_pages--;
h->free_huge_pages_node[nid]--;
return page;
@@ -1505,6 +1522,7 @@ static void prep_new_huge_page(struct hs
spin_lock(&hugetlb_lock);
h->nr_huge_pages++;
h->nr_huge_pages_node[nid]++;
+ ClearPageHugeFreed(page);
spin_unlock(&hugetlb_lock);
}
@@ -1771,6 +1789,14 @@ int dissolve_free_huge_page(struct page
int nid = page_to_nid(head);
if (h->free_huge_pages - h->resv_huge_pages == 0)
goto out;
+
+ /*
+ * We should make sure that the page is already on the free list
+ * when it is dissolved.
+ */
+ if (unlikely(!PageHugeFreed(head)))
+ goto out;
+
/*
* Move PageHWPoison flag from head page to the raw error page,
* which makes any subpages rather than the error page reusable.
_
Patches currently in -mm which might be from songmuchun@xxxxxxxxxxxxx are
mm-hugetlbfs-fix-cannot-migrate-the-fallocated-hugetlb-page.patch
mm-hugetlb-fix-a-race-between-freeing-and-dissolving-the-page.patch
mm-hugetlb-fix-a-race-between-isolating-and-freeing-page.patch
mm-hugetlb-remove-vm_bug_on_page-from-page_huge_active.patch
mm-memcontrol-optimize-per-lruvec-stats-counter-memory-usage.patch
mm-memcontrol-fix-nr_anon_thps-accounting-in-charge-moving.patch
mm-memcontrol-convert-nr_anon_thps-account-to-pages.patch
mm-memcontrol-convert-nr_file_thps-account-to-pages.patch
mm-memcontrol-convert-nr_shmem_thps-account-to-pages.patch
mm-memcontrol-convert-nr_shmem_pmdmapped-account-to-pages.patch
mm-memcontrol-convert-nr_file_pmdmapped-account-to-pages.patch
mm-memcontrol-make-the-slab-calculation-consistent.patch
mm-migrate-do-not-migrate-hugetlb-page-whose-refcount-is-one.patch
mm-hugetlb-add-return-eagain-for-dissolve_free_huge_page.patch
