From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-5.4 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 9CE10C32759 for ; Wed, 14 Aug 2019 20:32:22 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 6C78A216F4 for ; Wed, 14 Aug 2019 20:32:22 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=nvidia.com header.i=@nvidia.com header.b="bWazUH1o" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727652AbfHNUcV (ORCPT ); Wed, 14 Aug 2019 16:32:21 -0400 Received: from hqemgate15.nvidia.com ([216.228.121.64]:6708 "EHLO hqemgate15.nvidia.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726221AbfHNUcU (ORCPT ); Wed, 14 Aug 2019 16:32:20 -0400 Received: from hqpgpgate102.nvidia.com (Not Verified[216.228.121.13]) by hqemgate15.nvidia.com (using TLS: TLSv1.2, DES-CBC3-SHA) id ; Wed, 14 Aug 2019 13:32:31 -0700 Received: from hqmail.nvidia.com ([172.20.161.6]) by hqpgpgate102.nvidia.com (PGP Universal service); Wed, 14 Aug 2019 13:32:20 -0700 X-PGP-Universal: processed; by hqpgpgate102.nvidia.com on Wed, 14 Aug 2019 13:32:20 -0700 Received: from rcampbell-dev.nvidia.com (10.124.1.5) by HQMAIL107.nvidia.com (172.20.187.13) with Microsoft SMTP Server (TLS) id 15.0.1473.3; Wed, 14 Aug 2019 20:32:13 +0000 Subject: Re: [PATCH v3 hmm 02/11] mm/mmu_notifiers: do not speculatively allocate a mmu_notifier_mm To: Jason Gunthorpe , CC: Andrea Arcangeli , Christoph Hellwig , John Hubbard , =?UTF-8?B?SsOpcsO0bWUgR2xpc3Nl?= , "Kuehling, Felix" , "Alex Deucher" , =?UTF-8?Q?Christian_K=c3=b6nig?= , "David (ChunMing) Zhou" , Dimitri Sivanich , , , , , , , Gavin Shan , Andrea Righi , Jason Gunthorpe References: <20190806231548.25242-1-jgg@ziepe.ca> <20190806231548.25242-3-jgg@ziepe.ca> X-Nvconfidentiality: public From: Ralph Campbell Message-ID: Date: Wed, 14 Aug 2019 13:32:13 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.7.0 MIME-Version: 1.0 In-Reply-To: <20190806231548.25242-3-jgg@ziepe.ca> X-Originating-IP: [10.124.1.5] X-ClientProxiedBy: HQMAIL105.nvidia.com (172.20.187.12) To HQMAIL107.nvidia.com (172.20.187.13) Content-Type: text/plain; charset="utf-8"; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=nvidia.com; s=n1; t=1565814751; bh=q5g/jOMKlOwEYLFivYM3g535tx3Zkm1ReT5LriUi6Cs=; h=X-PGP-Universal:Subject:To:CC:References:X-Nvconfidentiality:From: Message-ID:Date:User-Agent:MIME-Version:In-Reply-To: X-Originating-IP:X-ClientProxiedBy:Content-Type:Content-Language: Content-Transfer-Encoding; b=bWazUH1oIGAphw/LWLwGrPnKZAno5v5obKf5t/eNR0RapozA5skQevZ5NNUWMTqSs kQOZhem/RWC7YrXGqUQcoX9RNPOMaSjczbb19BupGsQlBWLQzrHehLyn5MRQxPoeRz uRp+VPoBZXaU5WWDPyHzy/zn86IiYdKiYmtZuXSgMvZILtqwXmEIOyiTigq4o1+c8b VlbXt4UAjtud+BNmrZDyOUAgEsUrePtigZDeaGw1BwQ9WQfGiUlfYRa7z7VO+ymAOg wk1HgI2Ck8lmve8YFdkbz1IbY9uFTOy/smB0ozBuN1+Xs3FmWnPICy4oobSEcCxgmw VWUvGnEtlLyrQ== Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 8/6/19 4:15 PM, Jason Gunthorpe wrote: > From: Jason Gunthorpe > > A prior commit e0f3c3f78da2 ("mm/mmu_notifier: init notifier if necessary") > made an attempt at doing this, but had to be reverted as calling > the GFP_KERNEL allocator under the i_mmap_mutex causes deadlock, see > commit 35cfa2b0b491 ("mm/mmu_notifier: allocate mmu_notifier in advance"). > > However, we can avoid that problem by doing the allocation only under > the mmap_sem, which is already happening. > > Since all writers to mm->mmu_notifier_mm hold the write side of the > mmap_sem reading it under that sem is deterministic and we can use that to > decide if the allocation path is required, without speculation. > > The actual update to mmu_notifier_mm must still be done under the > mm_take_all_locks() to ensure read-side coherency. > > Signed-off-by: Jason Gunthorpe Looks good to me. Reviewed-by: Ralph Campbell