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Thu, 05 Sep 2024 03:55:21 -0700 (PDT) Received: from [10.4.59.158] ([139.177.225.242]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-2d8b8fe1f68sm9312094a91.31.2024.09.05.03.55.15 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 05 Sep 2024 03:55:21 -0700 (PDT) Message-ID: <03ebc281-c8e1-461b-a716-be6162947d31@bytedance.com> Date: Thu, 5 Sep 2024 18:55:11 +0800 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 08/14] mm: copy_pte_range() use pte_offset_map_rw_nolock() Content-Language: en-US To: Muchun Song Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-arm-kernel@lists.infradead.org, linuxppc-dev@lists.ozlabs.org, david@redhat.com, hughd@google.com, willy@infradead.org, vbabka@kernel.org, akpm@linux-foundation.org, rppt@kernel.org, vishal.moola@gmail.com, peterx@redhat.com, ryan.roberts@arm.com, christophe.leroy2@cs-soprasteria.com References: <20240904084022.32728-1-zhengqi.arch@bytedance.com> <20240904084022.32728-9-zhengqi.arch@bytedance.com> From: Qi Zheng In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 2024/9/5 16:57, Muchun Song wrote: > > > On 2024/9/4 16:40, Qi Zheng wrote: >> In copy_pte_range(), we may modify the src_pte entry after holding the >> src_ptl, so convert it to using pte_offset_map_rw_nolock(). Since we may >> free the PTE page in retract_page_tables() without holding the read lock >> of mmap_lock, so we still need to get pmdval and do pmd_same() check >> after >> the ptl is held. > > See commit 3db82b9374ca92, copy_pte_range and retract_page_tables > are using vma->anon_vma to be exclusive. > > retract_page_tables()                    copy_page_range() >     vma_interval_tree_foreach()              if (!vma_needs_copy()) >         if (READ_ONCE(vma->anon_vma))            return 0; >             continue;                        copy_pte_range() > > So I think mmap write lock here is also used for keeping ->anon_vma stable. > And we do not need pmd_same(). Indeed, will change it in v4. Thanks! > > Muchun, > Thanks. >> >> Signed-off-by: Qi Zheng >> --- >> Hi Muchun, since the code has changed, I dropped your Reviewed-by tag >> here. >> >>   mm/memory.c | 18 +++++++++++++++++- >>   1 file changed, 17 insertions(+), 1 deletion(-) >> >> diff --git a/mm/memory.c b/mm/memory.c >> index 06674f94b7a4e..47974cc4bd7f2 100644 >> --- a/mm/memory.c >> +++ b/mm/memory.c >> @@ -1082,6 +1082,7 @@ copy_pte_range(struct vm_area_struct *dst_vma, >> struct vm_area_struct *src_vma, >>       struct mm_struct *src_mm = src_vma->vm_mm; >>       pte_t *orig_src_pte, *orig_dst_pte; >>       pte_t *src_pte, *dst_pte; >> +    pmd_t pmdval; >>       pte_t ptent; >>       spinlock_t *src_ptl, *dst_ptl; >>       int progress, max_nr, ret = 0; >> @@ -1107,13 +1108,28 @@ copy_pte_range(struct vm_area_struct *dst_vma, >> struct vm_area_struct *src_vma, >>           ret = -ENOMEM; >>           goto out; >>       } >> -    src_pte = pte_offset_map_nolock(src_mm, src_pmd, addr, &src_ptl); >> + >> +    /* >> +     * Since we may free the PTE page in retract_page_tables() without >> +     * holding the read lock of mmap_lock, so we still need to do a >> +     * pmd_same() check after holding the PTL. >> +     */ >> +    src_pte = pte_offset_map_rw_nolock(src_mm, src_pmd, addr, &pmdval, >> +                       &src_ptl); >>       if (!src_pte) { >>           pte_unmap_unlock(dst_pte, dst_ptl); >>           /* ret == 0 */ >>           goto out; >>       } >>       spin_lock_nested(src_ptl, SINGLE_DEPTH_NESTING); >> + >> +    if (unlikely(!pmd_same(pmdval, pmdp_get_lockless(src_pmd)))) { >> +        pte_unmap_unlock(src_pte, src_ptl); >> +        pte_unmap_unlock(dst_pte, dst_ptl); >> +        /* ret == 0 */ >> +        goto out; >> +    } >> + >>       orig_src_pte = src_pte; >>       orig_dst_pte = dst_pte; >>       arch_enter_lazy_mmu_mode(); >