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=-12.3 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 E7CEDC47082 for ; Wed, 26 May 2021 06:13:41 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id CF061613C9 for ; Wed, 26 May 2021 06:13:41 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232903AbhEZGPL (ORCPT ); Wed, 26 May 2021 02:15:11 -0400 Received: from mout.gmx.net ([212.227.17.20]:56153 "EHLO mout.gmx.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232350AbhEZGPK (ORCPT ); Wed, 26 May 2021 02:15:10 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=gmx.net; s=badeba3b8450; t=1622009611; bh=KxgWeHfxFfUb6Gv0RYGmvh4jtC6GycYtBhkPxNEiLY0=; h=X-UI-Sender-Class:Subject:To:Cc:References:From:Date:In-Reply-To; b=llZdYF9IKzwVI8TBihyK4zlZzBCkoz5pR9MVog4mJwXQVCTwEyj5+ITcCgK6T1JxY HFOzMg7q3oC+4/pTVYJNEsCQjnuKrSSV7gtq0KqOBVL50k7vJqRnGBDYICtW/BFnzp xH8pZcqVPkLQKg1f6g1yQfB5UmoaScXsWghaZ4xE= X-UI-Sender-Class: 01bb95c1-4bf8-414a-932a-4f6e2808ef9c Received: from [0.0.0.0] ([149.28.201.231]) by mail.gmx.net (mrgmx105 [212.227.17.174]) with ESMTPSA (Nemesis) id 1MUGeB-1lukq91OfT-00RLqB; Wed, 26 May 2021 08:13:30 +0200 Subject: Re: [PATCH] btrfs: relocation: fix misplaced barrier in reloc_root_is_dead To: Baptiste Lepers Cc: Chris Mason , Josef Bacik , David Sterba , Qu Wenruo , linux-btrfs@vger.kernel.org, linux-kernel@vger.kernel.org References: <20210526060947.26159-1-baptiste.lepers@gmail.com> From: Qu Wenruo Message-ID: <9fcd47ac-2642-88be-1bf0-7b920baefb10@gmx.com> Date: Wed, 26 May 2021 14:13:25 +0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.10.1 MIME-Version: 1.0 In-Reply-To: <20210526060947.26159-1-baptiste.lepers@gmail.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: quoted-printable X-Provags-ID: V03:K1:faF+UzofNDGJzyvBV9ZdiJ9SvU9svIoL4IA1ZAHTd1jXRfYLaCl XAJRJvb7Npd190Vb1QayCDnHfdq5UDDx3KTAa7nSN4ug6L1VRszEnHJuT0k079LqhpaTm66 wIgNaTWn9/iQlYRKh3Az0qqgiKan8Fwu1B/dJVf6ck5ed//3dctyUX7slLfliwQyxXrZUcP BLSFqEohqW1HaLa2AKLZg== X-UI-Out-Filterresults: notjunk:1;V03:K0:4WC1wSO3Sf8=:u6JYmwTTyY6j8M6nsZfvfp jDwZYrU9eZ7eb7bnCIZ/8Qs+blHML/LlheICJA/F63rp5rCxuNFdrWYyRYiMIyx2fUWVBs0dS P8RpKOSeJd9oOjMd7cZ/tBmLrbjqZWykIpQTlatsMK/mtQlXN7045yDtxVdOiq7GjkLl54UiR PfjECtGn5XqYwsd+speVMAR6m9XDK6EUG25D+A8VLGr9BP1iIk8Er1XVyJCzWevwzpGv/zxYR BZvpUCiWkfJUVfcEnRRRP43eLwPLp11INcQOXzQOlq72FuQEvkeyHK5CEtDyJLYvRsW+SkHuW JXXfnS2v42tGCTRNPFdZ8AblrtfE8Tsh/dpJzeUSWdeik2l0CwlYyo7x+Hz/AyKzXnCMjh4Zu NHZsYboqwO2dpJYoBr7svDc4fjiG4q28GzM+4CZUBtaIlza+nNeTBInFph/KgLDYiUTFeSjmr TkRUvwJtJfg6+wmFBc9QQiTTVBWRdxkYnUNY1Xa5VAE2Hqy4h6FZesC6dgMtII/+5uFJ0x0oF lfl6OVOBt6G33LMuZGaEYdt/TsIjFEHmZFKvTn7flY0l3dvLmIvORL+KeZYCgm27YSR/h8qoS SgqQpQZQA5tmirGSXJljLt0XJYeMV3ODiRD7ivdTyq2E90bgH1D3O1EJpOmosedgT9Z6Zqj+7 4fz2zg4pmgY/FZ7/arkQSbUZ166kf+l+s3i2vBohl5XQWgCWZO4TaTMeqHeyic2azy8Tu84/2 psfioQlns/1199GcAZq4/ctFKgT7yjxb9mvcmhKkQKAJOSASguY49YIUYOshzl1neplk5VYy2 334WfQkna8gJwW0w9dt2nqvYmKJaKhlSmSlkKE1BRx10v3725zXe/M0E33Pxo92ZeyxBYDSY8 ZK+GQ8lhEM0UAHEf0tVO0UF0rFH3/Mt5yLZwKcXT0v+/+I3cXa2Y75dSmaGd3nOoaLxKnal/E xSNK7f3wFUnXsbD3/+vWwhWcEXVLfzpN4Gf3VwFIDH1wlTk6bPtvlPPySJZ9kcwqZTYvNrgzw wIieP9RUj8Y9CcXq6fzqqV6EICjd2IMPZUIOJoLjoYrFbntQE19ICHBFljChsrlX+Aq2sHPHB FRWTSy2EPNcVF7/cDo/LcsagirMJodMmICk4pGW1o8oTh55xOJao6Aivw== Precedence: bulk List-ID: X-Mailing-List: linux-btrfs@vger.kernel.org On 2021/5/26 =E4=B8=8B=E5=8D=882:09, Baptiste Lepers wrote: > Fix a misplaced barrier in reloc_root_is_dead. The > BTRFS_ROOT_DEAD_RELOC_TREE bit should be checked before accessing > reloc_root. > > The fix forces the order documented in the original commit: > "In the cross section C-D, either caller gets the DEAD bit set, avoiding > access reloc_root no matter if it's safe or not. Or caller get the DEAD > bit cleared, then access reloc_root, which is already NULL, nothing will > be wrong." > > static bool reloc_root_is_dead() > smp_rmb(); <--- misplaced > if (test_bit(BTRFS_ROOT_DEAD_RELOC_TREE, &root->state)) > return true; > return false; > } Exactly what I originally purposed to David, we didn't reach an agreement on where the barrier should be. At least I'm completely fine with this patch. Reviewed-by: Qu Wenruo Thanks, Qu > > static bool have_reloc_root(struct btrfs_root *root) > { > if (reloc_root_is_dead(root)) > return false; > <--- the barrier should happen here > if (!root->reloc_root) > return false; > return true; > } > > Fixes: 6282675e6708e ("btrfs: relocation: fix reloc_root lifespan and ac= cess") > Signed-off-by: Baptiste Lepers > --- > fs/btrfs/relocation.c | 5 ++--- > 1 file changed, 2 insertions(+), 3 deletions(-) > > diff --git a/fs/btrfs/relocation.c b/fs/btrfs/relocation.c > index b70be2ac2e9e..8cddcce56bf4 100644 > --- a/fs/btrfs/relocation.c > +++ b/fs/btrfs/relocation.c > @@ -289,15 +289,14 @@ static int update_backref_cache(struct btrfs_trans= _handle *trans, > > static bool reloc_root_is_dead(struct btrfs_root *root) > { > + bool is_dead =3D test_bit(BTRFS_ROOT_DEAD_RELOC_TREE, &root->state); > /* > * Pair with set_bit/clear_bit in clean_dirty_subvols and > * btrfs_update_reloc_root. We need to see the updated bit before > * trying to access reloc_root > */ > smp_rmb(); > - if (test_bit(BTRFS_ROOT_DEAD_RELOC_TREE, &root->state)) > - return true; > - return false; > + return is_dead; > } > > /* >