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Thu, 05 Sep 2024 03:56:20 -0700 (PDT) Received: from [10.4.59.158] ([139.177.225.242]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-2d8b8fe1f68sm9312094a91.31.2024.09.05.03.56.14 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 05 Sep 2024 03:56:20 -0700 (PDT) Message-ID: Date: Thu, 5 Sep 2024 18:56:14 +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 09/14] mm: mremap: move_ptes() 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> <20240904084022.32728-10-zhengqi.arch@bytedance.com> <1b03a7de-1278-4e36-8068-885dd1c29742@linux.dev> From: Qi Zheng In-Reply-To: <1b03a7de-1278-4e36-8068-885dd1c29742@linux.dev> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 2024/9/5 17:25, Muchun Song wrote: > > > On 2024/9/4 16:40, Qi Zheng wrote: >> In move_ptes(), we may modify the new_pte after acquiring the new_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 do a pmd_same() check after holding the PTL. > > retract_page_tables() and move_ptes() are synchronized with > i_mmap_lock, right? Right, will remove the pmd_same() check in v4. Thanks! > > Muchun, > Thanks. > >> >> Signed-off-by: Qi Zheng >> --- >>   mm/mremap.c | 20 ++++++++++++++++++-- >>   1 file changed, 18 insertions(+), 2 deletions(-) >> >> diff --git a/mm/mremap.c b/mm/mremap.c >> index 24712f8dbb6b5..16e54151395ad 100644 >> --- a/mm/mremap.c >> +++ b/mm/mremap.c >> @@ -143,6 +143,7 @@ static int move_ptes(struct vm_area_struct *vma, >> pmd_t *old_pmd, >>       spinlock_t *old_ptl, *new_ptl; >>       bool force_flush = false; >>       unsigned long len = old_end - old_addr; >> +    pmd_t pmdval; >>       int err = 0; >>       /* >> @@ -175,14 +176,29 @@ static int move_ptes(struct vm_area_struct *vma, >> pmd_t *old_pmd, >>           err = -EAGAIN; >>           goto out; >>       } >> -    new_pte = pte_offset_map_nolock(mm, new_pmd, new_addr, &new_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. >> +     */ >> +    new_pte = pte_offset_map_rw_nolock(mm, new_pmd, new_addr, &pmdval, >> +                       &new_ptl); >>       if (!new_pte) { >>           pte_unmap_unlock(old_pte, old_ptl); >>           err = -EAGAIN; >>           goto out; >>       } >> -    if (new_ptl != old_ptl) >> +    if (new_ptl != old_ptl) { >>           spin_lock_nested(new_ptl, SINGLE_DEPTH_NESTING); >> + >> +        if (unlikely(!pmd_same(pmdval, pmdp_get_lockless(new_pmd)))) { >> +            pte_unmap_unlock(new_pte, new_ptl); >> +            pte_unmap_unlock(old_pte, old_ptl); >> +            err = -EAGAIN; >> +            goto out; >> +        } >> +    } >> + >>       flush_tlb_batched_pending(vma->vm_mm); >>       arch_enter_lazy_mmu_mode(); >