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[209.85.208.179]) by smtp.gmail.com with ESMTPSA id a12sm1824524ljk.34.2021.05.24.10.16.59 for (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 24 May 2021 10:16:59 -0700 (PDT) Received: by mail-lj1-f179.google.com with SMTP id f12so34593168ljp.2 for ; Mon, 24 May 2021 10:16:59 -0700 (PDT) X-Received: by 2002:a2e:968e:: with SMTP id q14mr17720803lji.507.1621876618963; Mon, 24 May 2021 10:16:58 -0700 (PDT) MIME-Version: 1.0 References: <20210524133818.84955-1-aneesh.kumar@linux.ibm.com> In-Reply-To: <20210524133818.84955-1-aneesh.kumar@linux.ibm.com> From: Linus Torvalds Date: Mon, 24 May 2021 07:16:43 -1000 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH v6 updated 9/11] mm/mremap: Fix race between mremap and pageout To: "Aneesh Kumar K.V" Cc: Linux-MM , Andrew Morton , Michael Ellerman , linuxppc-dev , Kalesh Singh , Nick Piggin , Joel Fernandes , Christophe Leroy Content-Type: text/plain; charset="UTF-8" Authentication-Results: imf09.hostedemail.com; dkim=pass header.d=linux-foundation.org header.s=google header.b=cV5W3NmA; dmarc=none; spf=pass (imf09.hostedemail.com: domain of torvalds@linuxfoundation.org designates 209.85.208.172 as permitted sender) smtp.mailfrom=torvalds@linuxfoundation.org X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 6DCD86000259 X-Stat-Signature: dqw1dtkys55yged9jjmueht8qy7ed88x X-HE-Tag: 1621876619-527242 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Mon, May 24, 2021 at 3:38 AM Aneesh Kumar K.V wrote: > > Avoid the above race with MOVE_PMD by holding pte ptl in mremap and waiting for > parallel pagetable walk to finish operating on pte before updating new_pmd Ack on the concept. However, not so much on the patch. Odd whitespace change: > @@ -254,6 +254,7 @@ static bool move_normal_pmd(struct vm_area_struct *vma, unsigned long old_addr, > if (WARN_ON_ONCE(!pmd_none(*new_pmd))) > return false; > > + > /* > * We don't have to worry about the ordering of src and dst > * ptlocks because exclusive mmap_lock prevents deadlock. And new optimization for empty pmd, which seems unrelated to the change and should presumably be separate: > @@ -263,6 +264,10 @@ static bool move_normal_pmd(struct vm_area_struct *vma, unsigned long old_addr, > if (new_ptl != old_ptl) > spin_lock_nested(new_ptl, SINGLE_DEPTH_NESTING); > > + if (pmd_none(*old_pmd)) > + goto unlock_out; > + > + pte_ptl = pte_lockptr(mm, old_pmd); > /* Clear the pmd */ > pmd = *old_pmd; > pmd_clear(old_pmd); And also, why does the above assign 'pte_ptl' without using it, when the actual use is ten lines further down? So I think this patch needs some cleanup. Linus