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[209.132.183.28]) by mx.google.com with ESMTPS id j96si1409762qte.111.2019.03.02.23.27.04 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Sat, 02 Mar 2019 23:27:04 -0800 (PST) Received-SPF: pass (google.com: domain of jstancek@redhat.com designates 209.132.183.28 as permitted sender) client-ip=209.132.183.28; Authentication-Results: mx.google.com; spf=pass (google.com: domain of jstancek@redhat.com designates 209.132.183.28 as permitted sender) smtp.mailfrom=jstancek@redhat.com; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=redhat.com Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.phx2.redhat.com [10.5.11.14]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id C815981F0E; Sun, 3 Mar 2019 07:27:03 +0000 (UTC) Received: from colo-mx.corp.redhat.com (colo-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.20]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 7513B5D9CA; Sun, 3 Mar 2019 07:27:03 +0000 (UTC) Received: from zmail17.collab.prod.int.phx2.redhat.com (zmail17.collab.prod.int.phx2.redhat.com [10.5.83.19]) by colo-mx.corp.redhat.com (Postfix) with ESMTP id BAAAB1819AFE; Sun, 3 Mar 2019 07:27:02 +0000 (UTC) Date: Sun, 3 Mar 2019 02:27:02 -0500 (EST) From: Jan Stancek To: Andrea Arcangeli , peterz@infradead.org Cc: linux-mm@kvack.org, akpm@linux-foundation.org, willy@infradead.org, riel@surriel.com, mhocko@suse.com, ying huang , jrdr linux , jglisse@redhat.com, aneesh kumar , david@redhat.com, raquini@redhat.com, rientjes@google.com, kirill@shutemov.name, mgorman@techsingularity.net, linux-kernel@vger.kernel.org Message-ID: <701776300.4537344.1551598022408.JavaMail.zimbra@redhat.com> In-Reply-To: <20190302185144.GD31083@redhat.com> References: <20190302171043.GP11592@bombadil.infradead.org> <20190302185144.GD31083@redhat.com> Subject: Re: [PATCH v2] mm/memory.c: do_fault: avoid usage of stale vm_area_struct MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit X-Originating-IP: [10.40.204.28, 10.4.195.18] Thread-Topic: mm/memory.c: do_fault: avoid usage of stale vm_area_struct Thread-Index: pAmRXCN5CetzZ5PIfXitNyEm+tfURQ== X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.27]); Sun, 03 Mar 2019 07:27:04 +0000 (UTC) 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: ----- Original Message ----- > Hello Jan, > > On Sat, Mar 02, 2019 at 07:19:39PM +0100, Jan Stancek wrote: > > + struct mm_struct *vm_mm = READ_ONCE(vma->vm_mm); > > The vma->vm_mm cannot change under gcc there, so no need of > READ_ONCE. The release of mmap_sem has release semantics so the > vma->vm_mm access cannot be reordered after up_read(mmap_sem) either. > > Other than the above detail: > > Reviewed-by: Andrea Arcangeli Thank you for review, I dropped READ_ONCE and sent v3 with your Reviewed-by included. I also successfully re-ran tests over-night. > Would this not need a corresponding WRITE_ONCE() in vma_init() ? There's at least 2 context switches between, so I think it wouldn't matter. My concern was gcc optimizing out vm_mm, and vma->vm_mm access happening only after do_read_fault().