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. [1] http://lkml.kernel.org/r/1447938052-22165-1-git-send-email-aarcange@xxxxxxxxxx Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx> Reported-by: Andrea Arcangeli <aarcange@xxxxxxxxxx> --- v2: - fix build for !THP; - typos; --- include/linux/huge_mm.h | 5 +++++ mm/huge_memory.c | 6 +++--- mm/swap.c | 5 +++++ 3 files changed, 13 insertions(+), 3 deletions(-) diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h index 7008623e24b1..d7b9e5346fba 100644 --- a/include/linux/huge_mm.h +++ b/include/linux/huge_mm.h @@ -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); #else /* CONFIG_TRANSPARENT_HUGEPAGE */ #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) +{ + BUILD_BUG(); +} static inline struct page *follow_devmap_pmd(struct vm_area_struct *vma, unsigned long addr, pmd_t *pmd, int flags) diff --git a/mm/huge_memory.c b/mm/huge_memory.c index 820214137bc5..860c7dec197e 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -235,7 +235,7 @@ 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 @@ -1715,12 +1715,12 @@ int zap_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma, if (vma_is_dax(vma)) { spin_unlock(ptl); if (is_huge_zero_pmd(orig_pmd)) - put_huge_zero_page(); + 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)); atomic_long_dec(&tlb->mm->nr_ptes); spin_unlock(ptl); - put_huge_zero_page(); + tlb_remove_page(tlb, pmd_page(orig_pmd)); } else { struct page *page = pmd_page(orig_pmd); page_remove_rmap(page, true); diff --git a/mm/swap.c b/mm/swap.c index 09fe5e97714a..11915bd0f047 100644 --- a/mm/swap.c +++ b/mm/swap.c @@ -728,6 +728,11 @@ void release_pages(struct page **pages, int nr, bool cold) zone = NULL; } + if (is_huge_zero_page(page)) { + put_huge_zero_page(); + continue; + } + page = compound_head(page); if (!put_page_testzero(page)) continue; -- 2.8.0.rc3 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>