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[172.10.233.147]) by smtp.gmail.com with ESMTPSA id i67-20020a0df846000000b00559f1cb8444sm1824582ywf.70.2023.05.21.22.13.34 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 21 May 2023 22:13:36 -0700 (PDT) Date: Sun, 21 May 2023 22:13:33 -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 19/31] mm/mremap: retry if either pte_offset_map_*lock() fails In-Reply-To: <68a97fbe-5c1e-7ac6-72c-7b9c6290b370@google.com> Message-ID: <2d3fbfea-5884-8211-0cc-954afe25ae9c@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" move_ptes() return -EAGAIN if pte_offset_map_lock() of old fails, or if pte_offset_map_nolock() of new fails: move_page_tables() retry if so. But that does need a pmd_none() check inside, to stop endless loop when huge shmem is truncated (thank you to syzbot); and move_huge_pmd() must tolerate that a page table might have been allocated there just before (of course it would be more satisfying to remove the empty page table, but this is not a path worth optimizing). Signed-off-by: Hugh Dickins --- mm/huge_memory.c | 5 +++-- mm/mremap.c | 28 ++++++++++++++++++++-------- 2 files changed, 23 insertions(+), 10 deletions(-) diff --git a/mm/huge_memory.c b/mm/huge_memory.c index 624671aaa60d..d4bd5fa7c823 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -1760,9 +1760,10 @@ bool move_huge_pmd(struct vm_area_struct *vma, unsig= ned long old_addr, =20 /* * The destination pmd shouldn't be established, free_pgtables() - * should have release it. + * should have released it; but move_page_tables() might have already + * inserted a page table, if racing against shmem/file collapse. */ - if (WARN_ON(!pmd_none(*new_pmd))) { + if (!pmd_none(*new_pmd)) { VM_BUG_ON(pmd_trans_huge(*new_pmd)); return false; } diff --git a/mm/mremap.c b/mm/mremap.c index b11ce6c92099..1fc47b4f38d7 100644 --- a/mm/mremap.c +++ b/mm/mremap.c @@ -133,7 +133,7 @@ static pte_t move_soft_dirty_pte(pte_t pte) return pte; } =20 -static void move_ptes(struct vm_area_struct *vma, pmd_t *old_pmd, +static int move_ptes(struct vm_area_struct *vma, pmd_t *old_pmd, unsigned long old_addr, unsigned long old_end, struct vm_area_struct *new_vma, pmd_t *new_pmd, unsigned long new_addr, bool need_rmap_locks) @@ -143,6 +143,7 @@ static void move_ptes(struct vm_area_struct *vma, pmd_t= *old_pmd, spinlock_t *old_ptl, *new_ptl; bool force_flush =3D false; unsigned long len =3D old_end - old_addr; + int err =3D 0; =20 /* * When need_rmap_locks is true, we take the i_mmap_rwsem and anon_vma @@ -170,8 +171,16 @@ static void move_ptes(struct vm_area_struct *vma, pmd_= t *old_pmd, * pte locks because exclusive mmap_lock prevents deadlock. */ old_pte =3D pte_offset_map_lock(mm, old_pmd, old_addr, &old_ptl); - new_pte =3D pte_offset_map(new_pmd, new_addr); - new_ptl =3D pte_lockptr(mm, new_pmd); + if (!old_pte) { + err =3D -EAGAIN; + goto out; + } + new_pte =3D pte_offset_map_nolock(mm, new_pmd, new_addr, &new_ptl); + if (!new_pte) { + pte_unmap_unlock(old_pte, old_ptl); + err =3D -EAGAIN; + goto out; + } if (new_ptl !=3D old_ptl) spin_lock_nested(new_ptl, SINGLE_DEPTH_NESTING); flush_tlb_batched_pending(vma->vm_mm); @@ -208,8 +217,10 @@ static void move_ptes(struct vm_area_struct *vma, pmd_= t *old_pmd, spin_unlock(new_ptl); pte_unmap(new_pte - 1); pte_unmap_unlock(old_pte - 1, old_ptl); +out: if (need_rmap_locks) drop_rmap_locks(vma); + return err; } =20 #ifndef arch_supports_page_table_move @@ -537,6 +548,7 @@ unsigned long move_page_tables(struct vm_area_struct *v= ma, new_pmd =3D alloc_new_pmd(vma->vm_mm, vma, new_addr); if (!new_pmd) break; +again: if (is_swap_pmd(*old_pmd) || pmd_trans_huge(*old_pmd) || pmd_devmap(*old_pmd)) { if (extent =3D=3D HPAGE_PMD_SIZE && @@ -544,8 +556,6 @@ unsigned long move_page_tables(struct vm_area_struct *v= ma, old_pmd, new_pmd, need_rmap_locks)) continue; split_huge_pmd(vma, old_pmd, old_addr); - if (pmd_trans_unstable(old_pmd)) - continue; } else if (IS_ENABLED(CONFIG_HAVE_MOVE_PMD) && extent =3D=3D PMD_SIZE) { /* @@ -556,11 +566,13 @@ unsigned long move_page_tables(struct vm_area_struct = *vma, old_pmd, new_pmd, true)) continue; } - + if (pmd_none(*old_pmd)) + continue; if (pte_alloc(new_vma->vm_mm, new_pmd)) break; - move_ptes(vma, old_pmd, old_addr, old_addr + extent, new_vma, - new_pmd, new_addr, need_rmap_locks); + if (move_ptes(vma, old_pmd, old_addr, old_addr + extent, + new_vma, new_pmd, new_addr, need_rmap_locks) < 0) + goto again; } =20 mmu_notifier_invalidate_range_end(&range); --=20 2.35.3