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[209.132.183.28]) by mx.google.com with ESMTPS id t20si713327qtq.144.2019.03.02.10.00.12 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Sat, 02 Mar 2019 10:00:13 -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-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 5437AC04BD22; Sat, 2 Mar 2019 18:00:11 +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 0FB875D704; Sat, 2 Mar 2019 18:00:11 +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 3F9DC1819AFF; Sat, 2 Mar 2019 18:00:10 +0000 (UTC) Date: Sat, 2 Mar 2019 13:00:09 -0500 (EST) From: Jan Stancek To: Matthew Wilcox Cc: linux-mm@kvack.org, akpm@linux-foundation.org, peterz@infradead.org, riel@surriel.com, mhocko@suse.com, ying huang , jrdr linux , jglisse@redhat.com, aneesh kumar , david@redhat.com, aarcange@redhat.com, raquini@redhat.com, rientjes@google.com, kirill@shutemov.name, mgorman@techsingularity.net, linux-kernel@vger.kernel.org Message-ID: <913961507.4507772.1551549609679.JavaMail.zimbra@redhat.com> In-Reply-To: <20190302171043.GP11592@bombadil.infradead.org> References: <0b7a4604529e16ace8d65a42dac7c78582e7fb28.1551538524.git.jstancek@redhat.com> <20190302171043.GP11592@bombadil.infradead.org> Subject: Re: [PATCH] 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: [10.40.204.21, 10.4.195.4] Thread-Topic: mm/memory.c: do_fault: avoid usage of stale vm_area_struct Thread-Index: C10Zhz2Qec5wJx/oT6sHbvbZS5ZXDA== X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.31]); Sat, 02 Mar 2019 18:00:11 +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 ----- > On Sat, Mar 02, 2019 at 04:11:26PM +0100, Jan Stancek wrote: > > Problem is that "vmf->vma" used in do_fault() can become stale. > > Because mmap_sem may be released, other threads can come in, > > call munmap() and cause "vma" be returned to kmem cache, and > > get zeroed/re-initialized and re-used: > > > This patch pins mm_struct and stores its value, to avoid using > > potentially stale "vma" when calling pte_free(). > > OK, we need to cache the mm_struct, but why do we need the extra atomic op? > There's surely no way the mm can be freed while the thread is in the middle > of handling a fault. You're right, I was needlessly paranoid. > > ie I would drop these lines: I'll send v2. Thanks, Jan > > > + mmgrab(vm_mm); > > + > ... > > + > > + mmdrop(vm_mm); > > + >