Commit aa88b68c authored by Kirill A. Shutemov's avatar Kirill A. Shutemov Committed by Linus Torvalds
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thp: keep huge zero page pinned until tlb flush

Andrea has found[1] a race condition on MMU-gather based TLB flush vs
split_huge_page() or shrinker which frees huge zero under us (patch 1/2
and 2/2 respectively).

With new THP refcounting, we don't need patch 1/2: mmu_gather keeps the
page pinned until flush is complete and the pin prevents the page from
being split under us.

We still need patch 2/2.  This is simplified version of Andrea's patch.
We don't need fancy encoding.


Signed-off-by: default avatarKirill A. Shutemov <>
Reported-by: default avatarAndrea Arcangeli <>
Reviewed-by: default avatarAndrea Arcangeli <>
Cc: "Aneesh Kumar K.V" <>
Cc: Mel Gorman <>
Cc: Hugh Dickins <>
Cc: Johannes Weiner <>
Cc: Dave Hansen <>
Cc: Vlastimil Babka <>
Signed-off-by: default avatarAndrew Morton <>
Signed-off-by: default avatarLinus Torvalds <>
parent 66ee95d1
......@@ -152,6 +152,7 @@ static inline bool is_huge_zero_pmd(pmd_t pmd)
struct page *get_huge_zero_page(void);
void put_huge_zero_page(void);
#define HPAGE_PMD_SHIFT ({ BUILD_BUG(); 0; })
......@@ -208,6 +209,10 @@ static inline bool is_huge_zero_page(struct page *page)
return false;
static inline void put_huge_zero_page(void)
static inline struct page *follow_devmap_pmd(struct vm_area_struct *vma,
unsigned long addr, pmd_t *pmd, int flags)
......@@ -232,7 +232,7 @@ retry:
return READ_ONCE(huge_zero_page);
static void put_huge_zero_page(void)
void put_huge_zero_page(void)
* Counter should never go to zero here. Only shrinker can put
......@@ -1684,12 +1684,12 @@ int zap_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma,
if (vma_is_dax(vma)) {
if (is_huge_zero_pmd(orig_pmd))
tlb_remove_page(tlb, pmd_page(orig_pmd));
} else if (is_huge_zero_pmd(orig_pmd)) {
pte_free(tlb->mm, pgtable_trans_huge_withdraw(tlb->mm, pmd));
tlb_remove_page(tlb, pmd_page(orig_pmd));
} else {
struct page *page = pmd_page(orig_pmd);
page_remove_rmap(page, true);
......@@ -728,6 +728,11 @@ void release_pages(struct page **pages, int nr, bool cold)
zone = NULL;
if (is_huge_zero_page(page)) {
page = compound_head(page);
if (!put_page_testzero(page))
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