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[172.10.233.147]) by smtp.gmail.com with ESMTPSA id d63-20020a816842000000b0055a7ff0a5cdsm303405ywc.27.2023.06.08.18.45.06 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 08 Jun 2023 18:45:08 -0700 (PDT) Date: Thu, 8 Jun 2023 18:45:05 -0700 (PDT) From: Hugh Dickins X-X-Sender: hugh@ripple.attlocal.net To: Andrew Morton cc: Mike Kravetz , Mike Rapoport , "Kirill A. Shutemov" , Matthew Wilcox , David Hildenbrand , Suren Baghdasaryan , Qi Zheng , Yang Shi , Mel Gorman , Peter Xu , Peter Zijlstra , Will Deacon , Yu Zhao , Alistair Popple , Ralph Campbell , Ira Weiny , Steven Price , SeongJae Park , Lorenzo Stoakes , Huang Ying , Naoya Horiguchi , Christophe Leroy , Zack Rusin , Jason Gunthorpe , Axel Rasmussen , Anshuman Khandual , Pasha Tatashin , Miaohe Lin , Minchan Kim , Christoph Hellwig , Song Liu , Thomas Hellstrom , Ryan Roberts , linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: [PATCH v2 29/32] mm/memory: handle_pte_fault() use pte_offset_map_nolock() In-Reply-To: Message-ID: References: MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" handle_pte_fault() use pte_offset_map_nolock() to get the vmf.ptl which corresponds to vmf.pte, instead of pte_lockptr() being used later, when there's a chance that the pmd entry might have changed, perhaps to none, or to a huge pmd, with no split ptlock in its struct page. Remove its pmd_devmap_trans_unstable() call: pte_offset_map_nolock() will handle that case by failing. Update the "morph" comment above, looking forward to when shmem or file collapse to THP may not take mmap_lock for write (or not at all). do_numa_page() use the vmf->ptl from handle_pte_fault() at first, but refresh it when refreshing vmf->pte. do_swap_page()'s pte_unmap_same() (the thing that takes ptl to verify a two-part PAE orig_pte) use the vmf->ptl from handle_pte_fault() too; but do_swap_page() is also used by anon THP's __collapse_huge_page_swapin(), so adjust that to set vmf->ptl by pte_offset_map_nolock(). Signed-off-by: Hugh Dickins --- mm/khugepaged.c | 6 ++++-- mm/memory.c | 38 +++++++++++++------------------------- 2 files changed, 17 insertions(+), 27 deletions(-) diff --git a/mm/khugepaged.c b/mm/khugepaged.c index 49cfa7cdfe93..c11db2e78e95 100644 --- a/mm/khugepaged.c +++ b/mm/khugepaged.c @@ -1005,6 +1005,7 @@ static int __collapse_huge_page_swapin(struct mm_stru= ct *mm, unsigned long address, end =3D haddr + (HPAGE_PMD_NR * PAGE_SIZE); int result; pte_t *pte =3D NULL; + spinlock_t *ptl; =20 for (address =3D haddr; address < end; address +=3D PAGE_SIZE) { struct vm_fault vmf =3D { @@ -1016,7 +1017,7 @@ static int __collapse_huge_page_swapin(struct mm_stru= ct *mm, }; =20 if (!pte++) { - pte =3D pte_offset_map(pmd, address); + pte =3D pte_offset_map_nolock(mm, pmd, address, &ptl); if (!pte) { mmap_read_unlock(mm); result =3D SCAN_PMD_NULL; @@ -1024,11 +1025,12 @@ static int __collapse_huge_page_swapin(struct mm_st= ruct *mm, } } =20 - vmf.orig_pte =3D *pte; + vmf.orig_pte =3D ptep_get_lockless(pte); if (!is_swap_pte(vmf.orig_pte)) continue; =20 vmf.pte =3D pte; + vmf.ptl =3D ptl; ret =3D do_swap_page(&vmf); /* Which unmaps pte (after perhaps re-checking the entry) */ pte =3D NULL; diff --git a/mm/memory.c b/mm/memory.c index c7b920291a72..4ec46eecefd3 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -2786,10 +2786,9 @@ static inline int pte_unmap_same(struct vm_fault *vm= f) int same =3D 1; #if defined(CONFIG_SMP) || defined(CONFIG_PREEMPTION) if (sizeof(pte_t) > sizeof(unsigned long)) { - spinlock_t *ptl =3D pte_lockptr(vmf->vma->vm_mm, vmf->pmd); - spin_lock(ptl); + spin_lock(vmf->ptl); same =3D pte_same(*vmf->pte, vmf->orig_pte); - spin_unlock(ptl); + spin_unlock(vmf->ptl); } #endif pte_unmap(vmf->pte); @@ -4696,7 +4695,6 @@ static vm_fault_t do_numa_page(struct vm_fault *vmf) * validation through pte_unmap_same(). It's of NUMA type but * the pfn may be screwed if the read is non atomic. */ - vmf->ptl =3D pte_lockptr(vma->vm_mm, vmf->pmd); spin_lock(vmf->ptl); if (unlikely(!pte_same(*vmf->pte, vmf->orig_pte))) { pte_unmap_unlock(vmf->pte, vmf->ptl); @@ -4767,8 +4765,10 @@ static vm_fault_t do_numa_page(struct vm_fault *vmf) flags |=3D TNF_MIGRATED; } else { flags |=3D TNF_MIGRATE_FAIL; - vmf->pte =3D pte_offset_map(vmf->pmd, vmf->address); - spin_lock(vmf->ptl); + vmf->pte =3D pte_offset_map_lock(vma->vm_mm, vmf->pmd, + vmf->address, &vmf->ptl); + if (unlikely(!vmf->pte)) + goto out; if (unlikely(!pte_same(*vmf->pte, vmf->orig_pte))) { pte_unmap_unlock(vmf->pte, vmf->ptl); goto out; @@ -4897,27 +4897,16 @@ static vm_fault_t handle_pte_fault(struct vm_fault = *vmf) vmf->pte =3D NULL; vmf->flags &=3D ~FAULT_FLAG_ORIG_PTE_VALID; } else { - /* - * If a huge pmd materialized under us just retry later. Use - * pmd_trans_unstable() via pmd_devmap_trans_unstable() instead - * of pmd_trans_huge() to ensure the pmd didn't become - * pmd_trans_huge under us and then back to pmd_none, as a - * result of MADV_DONTNEED running immediately after a huge pmd - * fault in a different thread of this mm, in turn leading to a - * misleading pmd_trans_huge() retval. All we have to ensure is - * that it is a regular pmd that we can walk with - * pte_offset_map() and we can do that through an atomic read - * in C, which is what pmd_trans_unstable() provides. - */ - if (pmd_devmap_trans_unstable(vmf->pmd)) - return 0; /* * A regular pmd is established and it can't morph into a huge - * pmd from under us anymore at this point because we hold the - * mmap_lock read mode and khugepaged takes it in write mode. - * So now it's safe to run pte_offset_map(). + * pmd by anon khugepaged, since that takes mmap_lock in write + * mode; but shmem or file collapse to THP could still morph + * it into a huge pmd: just retry later if so. */ - vmf->pte =3D pte_offset_map(vmf->pmd, vmf->address); + vmf->pte =3D pte_offset_map_nolock(vmf->vma->vm_mm, vmf->pmd, + vmf->address, &vmf->ptl); + if (unlikely(!vmf->pte)) + return 0; vmf->orig_pte =3D ptep_get_lockless(vmf->pte); vmf->flags |=3D FAULT_FLAG_ORIG_PTE_VALID; =20 @@ -4936,7 +4925,6 @@ static vm_fault_t handle_pte_fault(struct vm_fault *v= mf) if (pte_protnone(vmf->orig_pte) && vma_is_accessible(vmf->vma)) return do_numa_page(vmf); =20 - vmf->ptl =3D pte_lockptr(vmf->vma->vm_mm, vmf->pmd); spin_lock(vmf->ptl); entry =3D vmf->orig_pte; if (unlikely(!pte_same(*vmf->pte, entry))) { --=20 2.35.3