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=-0.9 required=3.0 tests=DKIMWL_WL_MED,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS, URIBL_BLOCKED autolearn=ham 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 57DEBC5CFFE for ; Tue, 11 Dec 2018 18:53:41 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 1FF0820880 for ; Tue, 11 Dec 2018 18:53:41 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=kernel-dk.20150623.gappssmtp.com header.i=@kernel-dk.20150623.gappssmtp.com header.b="wXdc2B4E" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 1FF0820880 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=kernel.dk Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726881AbeLKSxk (ORCPT ); Tue, 11 Dec 2018 13:53:40 -0500 Received: from mail-it1-f195.google.com ([209.85.166.195]:35344 "EHLO mail-it1-f195.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726418AbeLKSxj (ORCPT ); Tue, 11 Dec 2018 13:53:39 -0500 Received: by mail-it1-f195.google.com with SMTP id p197so5641278itp.0 for ; Tue, 11 Dec 2018 10:53:39 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel-dk.20150623.gappssmtp.com; s=20150623; h=subject:from:to:cc:references:message-id:date:user-agent :mime-version:in-reply-to:content-language:content-transfer-encoding; bh=wbPAhLt2fDGBmcnE7/YRRo4I9EDR2wBe8YvC0vOSPac=; b=wXdc2B4EpN9c+0UAujOUgdRVT6IL8a3fB7/orBqfpIeHVIsPWAANq3hfIA3PBBihqa IDh4JyweU1u5ykci1qILXbIOErELix9YNECiL2Aaak5ILCzj79YODWJkd0rUdUIwF+v6 NmR+EkoNwRijYrvNl4HY7oNFfnRupd/UdYpFZneKz5J+1jShTfE7oxxm2Ogh4CCCB3CB WqQY1R846PwtpMZpwlgYD+gKYY0mHqNeRqP5hT1ES8E3v8PbCN781purOWHLxMWv6wb5 D8Db+X01ylXAe2J/MhLoqMH1wTRqu9ceMrOPyhxhPqqTHja1ZPN24wb0xb8QJe4PbT+s GbgA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:subject:from:to:cc:references:message-id:date :user-agent:mime-version:in-reply-to:content-language :content-transfer-encoding; bh=wbPAhLt2fDGBmcnE7/YRRo4I9EDR2wBe8YvC0vOSPac=; b=GxyaTg6zX8x9/W2hK3t3iIpJHK4K0hSMUHZ9K5jWvybmvZJBJlo/Y8Gnk/hKzMAmHo Je9ct9T8XBNkQiwBb70K2u3uNedC1RYg35mHpShMoU/0PLCseAd5yrUGTsoZ/Ttq3Qv4 9qqwZ8SURuwHpo3qa/6h62eOstVy52dCknA4qAUt9vpKaqC/USbEXtMKx/Y6/dJpQkDL hQ9baqgaYEo7cHr0kVlWzOSXluaJWpTiaWjY9t9PxKG0TiaUBjdiNJC5mxlje5K8xdxs TxrG9OTTWMeVD2kaqt94UQmzk7seOpPrwl7GYwubtIZPMJXVpsaCTA27ipTK0zKVcB2l aYmQ== X-Gm-Message-State: AA+aEWZhSWICnNcMQWHEQ4RN2/b3lF9yNLrGcMOj9ITQW7HNhGHlohD+ u3wiAVsUFuQlRVpsd9FAJ9wXdg== X-Google-Smtp-Source: AFSGD/UsU7wH4CShHVRMe8pyIJKZoQE36gZzDDaJ7rja7D/LXN2PEiy+clzFzX1yQCBlLWs0k8Btyg== X-Received: by 2002:a24:94f:: with SMTP id 76mr3419055itm.169.1544554418807; Tue, 11 Dec 2018 10:53:38 -0800 (PST) Received: from [192.168.1.56] ([216.160.245.98]) by smtp.gmail.com with ESMTPSA id t194sm9183769iof.3.2018.12.11.10.53.37 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 11 Dec 2018 10:53:37 -0800 (PST) Subject: Re: [PATCH] aio: Convert ioctx_table to XArray From: Jens Axboe To: Matthew Wilcox Cc: Al Viro , Benjamin LaHaise , Andrew Morton , Kees Cook , fsdevel , linux-aio@kvack.org, linux-mm , linux-kernel , Dan Carpenter References: <20181128183531.5139-1-willy@infradead.org> <09e3d156-66fc-ca17-efac-63f080a27a1d@kernel.dk> <20181211184553.GH6830@bombadil.infradead.org> <75267003-9407-101f-33ee-685e345a2c8a@kernel.dk> Message-ID: Date: Tue, 11 Dec 2018 11:53:36 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.2.1 MIME-Version: 1.0 In-Reply-To: <75267003-9407-101f-33ee-685e345a2c8a@kernel.dk> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 12/11/18 11:46 AM, Jens Axboe wrote: > On 12/11/18 11:45 AM, Matthew Wilcox wrote: >> On Tue, Dec 11, 2018 at 11:41:55AM -0700, Jens Axboe wrote: >>> On Wed, Nov 28, 2018 at 11:35 AM Matthew Wilcox wrote: >>>> >>>> rcu_read_lock(); >>>> - table = rcu_dereference(mm->ioctx_table); >>>> - >>>> - if (!table || id >= table->nr) >>>> - goto out; >>>> - >>>> - ctx = rcu_dereference(table->table[id]); >>>> + ctx = xa_load(&mm->ioctx, id); >>>> if (ctx && ctx->user_id == ctx_id) { >>>> if (percpu_ref_tryget_live(&ctx->users)) >>>> ret = ctx; >>>> } >>> >>> Question on this part - do we need that RCU read lock around this now? I >>> don't think we do. >> >> I think we need the rcu read lock here to prevent ctx from being freed >> under us by free_ioctx(). > > Then that begs the question, how about __xa_load() that is already called > under RCU read lock? Something like this, mem remap has an existing user that can use this too already. -- Jens Axboe