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=-8.4 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,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 6E704C10F26 for ; Fri, 6 Mar 2020 19:53:28 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 43C8720675 for ; Fri, 6 Mar 2020 19:53:28 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=joelfernandes.org header.i=@joelfernandes.org header.b="qk06El3J" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726269AbgCFTxZ (ORCPT ); Fri, 6 Mar 2020 14:53:25 -0500 Received: from mail-qv1-f68.google.com ([209.85.219.68]:41899 "EHLO mail-qv1-f68.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726083AbgCFTxZ (ORCPT ); Fri, 6 Mar 2020 14:53:25 -0500 Received: by mail-qv1-f68.google.com with SMTP id s15so1505213qvn.8 for ; Fri, 06 Mar 2020 11:53:24 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=joelfernandes.org; s=google; h=date:from:to:subject:message-id:references:mime-version :content-disposition:content-transfer-encoding:in-reply-to :user-agent; bh=QaNxcQb7Gg+vxIHDRqfm2dfWV4oEZhj/ZtvsBzj/+Bk=; b=qk06El3JD3uD38dR/+KpHsLyQqx2wruXRJgkstX2ahhw9X3IFGj5nLe2Z+o4giq/pM ldJs5F7oyuhAevtUXI557hIOqP78gga6BNTgb4Smwr0CdmuPgHBd9R/mpRAuAVFgT6Si FO4sdeP9aVDm3bSjSYygt3LXsi7uG2og5cDNg= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:subject:message-id:references :mime-version:content-disposition:content-transfer-encoding :in-reply-to:user-agent; bh=QaNxcQb7Gg+vxIHDRqfm2dfWV4oEZhj/ZtvsBzj/+Bk=; b=PXfc5V5wVHPAkKED9bCeroSaSjhsZ3djoS6SRyJ7lLA9+VNmsRhnVBButrq17rQDqT tMyRwwcD6cHXa2TVQEvfQ/7o3ZjxlQF9lGonvJUg9S4WTGos2qfUKg7hzsCrGVY12DJg 8pas2V7N+kkx1iA9dVqWzRc7ZMCSj/YO1rB0EC6kmkHYPSayPxIlYLIofFikmfoyT4XT 5EG+fJ8RgOgBblHcsSVBqnT96iYVQC+AmknogPyaneA8UPml0kpJlArewcjdUlrdUZiR 7pnv1GR21qSPul4ZkYZteDHsiXdHuOHyrNxlblEBTulRJ+qn4oJ5ZUVlfKiIQgPYfulf fjng== X-Gm-Message-State: ANhLgQ1d1vMCoBB3M+N2QMJb7V2BhA6n6IXDeyv6/lv8Qj3JYyaRN2t4 3UyD3l852jvDPiuI6fwsuszNC2ssx6c= X-Google-Smtp-Source: ADFU+vtbUmkkv8Fc33D5K6vbh/9sVOZA5kQ0oSPjOpP/B5uhae1bm0YKFhE+l4pQ9zfnhd2Fpzr5Rw== X-Received: by 2002:a05:6214:1051:: with SMTP id l17mr4508705qvr.175.1583524404428; Fri, 06 Mar 2020 11:53:24 -0800 (PST) Received: from localhost ([2620:15c:6:12:9c46:e0da:efbf:69cc]) by smtp.gmail.com with ESMTPSA id x188sm8961139qka.53.2020.03.06.11.53.23 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 06 Mar 2020 11:53:23 -0800 (PST) Date: Fri, 6 Mar 2020 14:53:23 -0500 From: Joel Fernandes To: dsterba@suse.cz, Madhuparna Bhowmik , Qu Wenruo , clm@fb.com, josef@toxicpanda.com, dsterba@suse.com, linux-btrfs@vger.kernel.org, linux-kernel@vger.kernel.org, linux-kernel-mentees@lists.linuxfoundation.org, paulmck@kernel.org, frextrite@gmail.com, linux@roeck-us.net Subject: Re: [PATCH] fs: btrfs: block-group.c: Fix suspicious RCU usage warning Message-ID: <20200306195323.GE60713@google.com> References: <20200306065243.11699-1-madhuparnabhowmik10@gmail.com> <20200306140023.GA14186@madhuparna-HP-Notebook> <20200306152527.GH2902@twin.jikos.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20200306152527.GH2902@twin.jikos.cz> User-Agent: Mutt/1.12.2 (2019-09-21) Sender: linux-btrfs-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-btrfs@vger.kernel.org On Fri, Mar 06, 2020 at 04:25:27PM +0100, David Sterba wrote: > On Fri, Mar 06, 2020 at 07:30:24PM +0530, Madhuparna Bhowmik wrote: > > On Fri, Mar 06, 2020 at 03:16:53PM +0800, Qu Wenruo wrote: > > > > > > > > > On 2020/3/6 下午2:52, madhuparnabhowmik10@gmail.com wrote: > > > > From: Madhuparna Bhowmik > > > > > > > > The space_info list is rcu protected. > > > > Hence, it should be traversed with rcu_read_lock held. > > > > > > > > Warning: > > > > [ 29.104591] ============================= > > > > [ 29.104756] WARNING: suspicious RCU usage > > > > [ 29.105046] 5.6.0-rc4-next-20200305 #1 Not tainted > > > > [ 29.105231] ----------------------------- > > > > [ 29.105401] fs/btrfs/block-group.c:2011 RCU-list traversed in non-reader section!! > > > > > > > > Reported-by: Guenter Roeck > > > > Signed-off-by: Madhuparna Bhowmik > > > > --- > > > > fs/btrfs/block-group.c | 4 +++- > > > > 1 file changed, 3 insertions(+), 1 deletion(-) > > > > > > > > diff --git a/fs/btrfs/block-group.c b/fs/btrfs/block-group.c > > > > index 404e050ce8ee..9cabeef66f5b 100644 > > > > --- a/fs/btrfs/block-group.c > > > > +++ b/fs/btrfs/block-group.c > > > > @@ -1987,6 +1987,7 @@ int btrfs_read_block_groups(struct btrfs_fs_info *info) > > > > > > This function is only triggered at mount time, where no other rcu > > > operation can happen. > > > > > Thanks Qu. > > > > Joel and Paul, what should we do in this case? > > Should we just pass cond = true or use list_for_each_entry instead? > > I think we can afford to add rcu lock/unlock, even if it's not strictly > necessary due to the single threaded context where the function is run. > There are some lightweight operations inside and inc_block_group starts > with two spin locks so there's nothing we'd be losing with disabled > preemption from the caller. I think use list_for_each_entry(). thanks, - Joel 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=-8.1 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, 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 806C2C10F25 for ; Fri, 6 Mar 2020 20:00:23 +0000 (UTC) Received: from hemlock.osuosl.org (smtp2.osuosl.org [140.211.166.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 3F02920709 for ; Fri, 6 Mar 2020 20:00:23 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (1024-bit key) header.d=joelfernandes.org header.i=@joelfernandes.org header.b="qk06El3J" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 3F02920709 Authentication-Results: mail.kernel.org; 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Fri, 06 Mar 2020 11:53:24 -0800 (PST) Received: from localhost ([2620:15c:6:12:9c46:e0da:efbf:69cc]) by smtp.gmail.com with ESMTPSA id x188sm8961139qka.53.2020.03.06.11.53.23 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 06 Mar 2020 11:53:23 -0800 (PST) Date: Fri, 6 Mar 2020 14:53:23 -0500 From: Joel Fernandes To: dsterba@suse.cz, Madhuparna Bhowmik , Qu Wenruo , clm@fb.com, josef@toxicpanda.com, dsterba@suse.com, linux-btrfs@vger.kernel.org, linux-kernel@vger.kernel.org, linux-kernel-mentees@lists.linuxfoundation.org, paulmck@kernel.org, frextrite@gmail.com, linux@roeck-us.net Message-ID: <20200306195323.GE60713@google.com> References: <20200306065243.11699-1-madhuparnabhowmik10@gmail.com> <20200306140023.GA14186@madhuparna-HP-Notebook> <20200306152527.GH2902@twin.jikos.cz> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20200306152527.GH2902@twin.jikos.cz> User-Agent: Mutt/1.12.2 (2019-09-21) Subject: Re: [Linux-kernel-mentees] [PATCH] fs: btrfs: block-group.c: Fix suspicious RCU usage warning X-BeenThere: linux-kernel-mentees@lists.linuxfoundation.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; 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