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[172.10.233.147]) by smtp.gmail.com with ESMTPSA id g189-20020a8152c6000000b00555e1886350sm1827794ywb.78.2023.05.21.21.58.59 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 21 May 2023 21:59:01 -0700 (PDT) Date: Sun, 21 May 2023 21:58:58 -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 , Naoya Horiguchi , Christophe Leroy , Zack Rusin , Jason Gunthorpe , Axel Rasmussen , Anshuman Khandual , Pasha Tatashin , Miaohe Lin , Minchan Kim , Christoph Hellwig , Song Liu , Thomas Hellstrom , linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: [PATCH 08/31] mm/page_vma_mapped: pte_offset_map_nolock() not pte_lockptr() In-Reply-To: <68a97fbe-5c1e-7ac6-72c-7b9c6290b370@google.com> Message-ID: <8fa3fb6e-2e39-cbea-c529-ee9e64c7d2d0@google.com> References: <68a97fbe-5c1e-7ac6-72c-7b9c6290b370@google.com> 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" map_pte() use pte_offset_map_nolock(), to make sure of the ptl belonging to pte, even if pmd entry is then changed racily: page_vma_mapped_walk() use that instead of getting pte_lockptr() later, or restart if map_pte() found no page table. Signed-off-by: Hugh Dickins --- mm/page_vma_mapped.c | 28 ++++++++++++++++++++++------ 1 file changed, 22 insertions(+), 6 deletions(-) diff --git a/mm/page_vma_mapped.c b/mm/page_vma_mapped.c index 947dc7491815..2af734274073 100644 --- a/mm/page_vma_mapped.c +++ b/mm/page_vma_mapped.c @@ -13,16 +13,28 @@ static inline bool not_found(struct page_vma_mapped_wal= k *pvmw) return false; } =20 -static bool map_pte(struct page_vma_mapped_walk *pvmw) +static bool map_pte(struct page_vma_mapped_walk *pvmw, spinlock_t **ptlp) { if (pvmw->flags & PVMW_SYNC) { /* Use the stricter lookup */ pvmw->pte =3D pte_offset_map_lock(pvmw->vma->vm_mm, pvmw->pmd, pvmw->address, &pvmw->ptl); - return true; + *ptlp =3D pvmw->ptl; + return !!pvmw->pte; } =20 - pvmw->pte =3D pte_offset_map(pvmw->pmd, pvmw->address); + /* + * It is important to return the ptl corresponding to pte, + * in case *pvmw->pmd changes underneath us; so we need to + * return it even when choosing not to lock, in case caller + * proceeds to loop over next ptes, and finds a match later. + * Though, in most cases, page lock already protects this. + */ + pvmw->pte =3D pte_offset_map_nolock(pvmw->vma->vm_mm, pvmw->pmd, + pvmw->address, ptlp); + if (!pvmw->pte) + return false; + if (pvmw->flags & PVMW_MIGRATION) { if (!is_swap_pte(*pvmw->pte)) return false; @@ -51,7 +63,7 @@ static bool map_pte(struct page_vma_mapped_walk *pvmw) } else if (!pte_present(*pvmw->pte)) { return false; } - pvmw->ptl =3D pte_lockptr(pvmw->vma->vm_mm, pvmw->pmd); + pvmw->ptl =3D *ptlp; spin_lock(pvmw->ptl); return true; } @@ -156,6 +168,7 @@ bool page_vma_mapped_walk(struct page_vma_mapped_walk *= pvmw) struct vm_area_struct *vma =3D pvmw->vma; struct mm_struct *mm =3D vma->vm_mm; unsigned long end; + spinlock_t *ptl; pgd_t *pgd; p4d_t *p4d; pud_t *pud; @@ -257,8 +270,11 @@ bool page_vma_mapped_walk(struct page_vma_mapped_walk = *pvmw) step_forward(pvmw, PMD_SIZE); continue; } - if (!map_pte(pvmw)) + if (!map_pte(pvmw, &ptl)) { + if (!pvmw->pte) + goto restart; goto next_pte; + } this_pte: if (check_pte(pvmw)) return true; @@ -281,7 +297,7 @@ bool page_vma_mapped_walk(struct page_vma_mapped_walk *= pvmw) } while (pte_none(*pvmw->pte)); =20 if (!pvmw->ptl) { - pvmw->ptl =3D pte_lockptr(mm, pvmw->pmd); + pvmw->ptl =3D ptl; spin_lock(pvmw->ptl); } goto this_pte; --=20 2.35.3