From c777e2a8b65420b31dac28a453e35be984f5808b Mon Sep 17 00:00:00 2001 From: "Aneesh Kumar K.V" Date: Tue, 9 Feb 2016 06:50:31 +0530 Subject: powerpc/mm: Fix Multi hit ERAT cause by recent THP update With ppc64 we use the deposited pgtable_t to store the hash pte slot information. We should not withdraw the deposited pgtable_t without marking the pmd none. This ensure that low level hash fault handling will skip this huge pte and we will handle them at upper levels. Recent change to pmd splitting changed the above in order to handle the race between pmd split and exit_mmap. The race is explained below. Consider following race: CPU0 CPU1 shrink_page_list() add_to_swap() split_huge_page_to_list() __split_huge_pmd_locked() pmdp_huge_clear_flush_notify() // pmd_none() == true exit_mmap() unmap_vmas() zap_pmd_range() // no action on pmd since pmd_none() == true pmd_populate() As result the THP will not be freed. The leak is detected by check_mm(): BUG: Bad rss-counter state mm:ffff880058d2e580 idx:1 val:512 The above required us to not mark pmd none during a pmd split. The fix for ppc is to clear the huge pte of _PAGE_USER, so that low level fault handling code skip this pte. At higher level we do take ptl lock. That should serialze us against the pmd split. Once the lock is acquired we do check the pmd again using pmd_same. That should always return false for us and hence we should retry the access. We do the pmd_same check in all case after taking plt with THP (do_huge_pmd_wp_page, do_huge_pmd_numa_page and huge_pmd_set_accessed) Also make sure we wait for irq disable section in other cpus to finish before flipping a huge pte entry with a regular pmd entry. Code paths like find_linux_pte_or_hugepte depend on irq disable to get a stable pte_t pointer. A parallel thp split need to make sure we don't convert a pmd pte to a regular pmd entry without waiting for the irq disable section to finish. Fixes: eef1b3ba053a ("thp: implement split_huge_pmd()") Acked-by: Kirill A. Shutemov Signed-off-by: Aneesh Kumar K.V Signed-off-by: Michael Ellerman --- include/asm-generic/pgtable.h | 8 ++++++++ 1 file changed, 8 insertions(+) (limited to 'include/asm-generic') diff --git a/include/asm-generic/pgtable.h b/include/asm-generic/pgtable.h index 0b3c0d39ef75..c370b261c720 100644 --- a/include/asm-generic/pgtable.h +++ b/include/asm-generic/pgtable.h @@ -239,6 +239,14 @@ extern void pmdp_invalidate(struct vm_area_struct *vma, unsigned long address, pmd_t *pmdp); #endif +#ifndef __HAVE_ARCH_PMDP_HUGE_SPLIT_PREPARE +static inline void pmdp_huge_split_prepare(struct vm_area_struct *vma, + unsigned long address, pmd_t *pmdp) +{ + +} +#endif + #ifndef __HAVE_ARCH_PTE_SAME static inline int pte_same(pte_t pte_a, pte_t pte_b) { -- cgit v1.2.3-59-g8ed1b