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=-2.1 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=no 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 28F9AC2D0CE for ; Fri, 24 Jan 2020 05:34:36 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id E4BDA2071E for ; Fri, 24 Jan 2020 05:34:35 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=aol.com header.i=@aol.com header.b="NxNxPOFz" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730373AbgAXFef (ORCPT ); Fri, 24 Jan 2020 00:34:35 -0500 Received: from sonic304-23.consmr.mail.gq1.yahoo.com ([98.137.68.204]:41893 "EHLO sonic304-23.consmr.mail.gq1.yahoo.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730338AbgAXFee (ORCPT ); Fri, 24 Jan 2020 00:34:34 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=aol.com; s=a2048; t=1579844073; bh=UeJz9jyBNt5yayp7xj4f/SZWo0DpuycvuaFMYq1D8lg=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From:Subject; b=NxNxPOFzSfORh0/j+CyjrCAXbIzvw6ZHJA0VT8plACOZ69yKZ55in66tkPbpWIcBeXRauEXemw1f9NZuEngyqU03g5dB2t0fRuOpKrpSqk8C7OW5sREI1tfvGJjw4vYKZ/lvWk3ek5sXuqAZt4K5kdJmwHm0MomdHvKzEawtNAehxb0CgxWxvNx+s99RX0sZNdPqqqSbCC6Aev27kzSxU6jkruWXIi0S0gL0xTj9CIwK1UdChRNGYcPS8deeuVlDZVq1SKvJ9xi1Y65+dhmbGqLOBiFGfdn31thYTepR1qhDojoNp+AVSFypKdEH2/fJUEGPrlDs7rirncqaTnWvYg== X-YMail-OSG: jpBgorYVM1niDtoaJJkIHlAQwijPN.6fSmZoI4.D5pZpqmPkPgbrgdCc3bajoGE 9NFLvAJZlQp9e_slnmrybNZnRd7.xfJeiO6p85yik1XdVrNwNPhSm7jC9gCYQpbQ1MkUkVhqXlP8 CbEPhu4VEYevwxrsg6VN3Rpigk9xLiQ0ucRw.WZKNCtGQ_AkCTxq_fYq_ss8sbV.95yBQIXJ0RSE zRDQNhHjjg.aO7x1BBPbsgppivpLGEgOiP7lO9Z.lhCBjTtlCBAVap3b1O1SDS1bjkBV8phceVDM nFcv_4kWg4jLu8D.dxw_dzp_fyrhpnFP.AFhMPhf_hhugMfXrsiPdNzfoREF07wZDwdbuPOML59U Oo7RuXpvNk6UbxfDveVZFmJHvf1oaNZGMjrZcOaGq0E6mUW45Op3kBteRJ.Syn1W.FigWSPEMjbl OmdiDgOaJ2ExqCMAvX9L_99nm25IX76gES9xIONRNAu.vzQsrhtppRKnGUS9YiZ3IvX6CndPC2.F 0wvZIz9aW8HHlg7FUPmiplPN91NmJrJ6aPO1noqJQSTV23HC38nDaMllXTr_GkK7TGnc94flHjou zwP0NLw8Sw_ajvTHDXIOSE4nKr08X0bJ8rqqwOl_HgHcte4Zoi1ZJqvUSiKA1UYOW27wzv8lcyrK e1WNg9KWHpUZHamY4taOgz8.8XNJ2F_i5RH4PapB4xFfr8cw9bAySh9Bkpy4VROqymI7I7JPY00q Iyy7E.wWJfM8ch.37t2vFxAqcqqm1PMlcXfeBQl9TFfNLq6cAKRZWsr8oNGp4HlJHApqOaFm1.Q4 8RNzJwUqJ87Crb3sx0unDxhoHpV6AiXotap4dvQmv_f7aLd0GrG5hUccDlTdPCEklvQeP9nIEZqv OPy6RwATC6wnGkKQseChbiXzfsybZbyNpXc6tfzCjki99l23c44E9ukJdbDmWKNQ95ga73oghi.I 97wQS8b3Vz9_x5Eh6yqw55CUvejzxvwFeM8DH4cskesjYGhgQQb2Vjr.AiPZeOu5d8umJZjTZG3g mcuTqSUCqRUF5C62h4Khc9AWYp57Mr59cTTFXwlCrSyYJFEp9l90dhncXdL4S.26.0SQ0vJvKhBZ X3BpqbjCVSdFOhNyzOnCp2_BrmCagUDAUATKCuedlydlI68tUQ_OkkkIHvOqoXSAO7meALGjHMsP OMISiC2VQSlwwKmGIDOFLJsDqTl6SLV1vDZ2r1nALsat6ul2TGkpmvM_q9AGMorgiS3LRghQWAvI z4EhmII8xNvwUT8cxPFrX06Yhfll.WNp7qiY6pMIb_ZkuZLaHhKochdff.I9l8U6QToEgzG0AEKD X1nwNxGlfh5jUxtNLWD267If67nf456b57TzIDkE1KOIbHMfgw4SLofRbwDWkPsZglTDkBaBnCWr 1advyz4RlnpkNGQ9QV.pBaXmwhD6r72hh8fiCGsLBbA-- Received: from sonic.gate.mail.ne1.yahoo.com by sonic304.consmr.mail.gq1.yahoo.com with HTTP; Fri, 24 Jan 2020 05:34:33 +0000 Received: by smtp432.mail.gq1.yahoo.com (Oath Hermes SMTP Server) with ESMTPA ID 5154e0a93daa76c8f17f548eb900f9b7; Fri, 24 Jan 2020 05:34:30 +0000 (UTC) Date: Fri, 24 Jan 2020 13:34:23 +0800 From: Gao Xiang To: Eric Biggers Cc: linux-ext4@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-f2fs-devel@lists.sourceforge.net, Alexander Viro , Daniel Rosenberg , Gabriel Krisman Bertazi Subject: Re: [PATCH] ext4: fix race conditions in ->d_compare() and ->d_hash() Message-ID: <20200124053415.GC31271@hsiangkao-HP-ZHAN-66-Pro-G1> References: <20200124041234.159740-1-ebiggers@kernel.org> <20200124050423.GA31271@hsiangkao-HP-ZHAN-66-Pro-G1> <20200124051601.GB832@sol.localdomain> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200124051601.GB832@sol.localdomain> User-Agent: Mutt/1.10.1 (2018-07-13) X-Mailer: WebService/1.1.14873 hermes Apache-HttpAsyncClient/4.1.4 (Java/1.8.0_181) Sender: linux-ext4-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-ext4@vger.kernel.org On Thu, Jan 23, 2020 at 09:16:01PM -0800, Eric Biggers wrote: [] > So we need READ_ONCE() to ensure that a consistent value is used. By the way, my understanding is all pointer could be accessed atomicly guaranteed by compiler. In my opinion, we generally use READ_ONCE() on pointers for other uses (such as, avoid accessing a variable twice due to compiler optimization and it will break some logic potentially or need some data dependency barrier...) Thanks, Gao Xiang