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=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 1297AC10F25 for ; Fri, 6 Mar 2020 19:53:27 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id D90BB20656 for ; Fri, 6 Mar 2020 19:53:26 +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 S1726397AbgCFTxZ (ORCPT ); Fri, 6 Mar 2020 14:53:25 -0500 Received: from mail-qv1-f66.google.com ([209.85.219.66]:39034 "EHLO mail-qv1-f66.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726162AbgCFTxZ (ORCPT ); Fri, 6 Mar 2020 14:53:25 -0500 Received: by mail-qv1-f66.google.com with SMTP id fc12so1515308qvb.6 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=KCmPmstc+KK8Tnct5yIPRZgaLs4FmqSA7kUvRHoD90FS9/ghViW9ao4OJcriHwEbTV QtOJm2e9+2Zo22XDFuRj+MF5oNNakhiwEBGhKK10u2ikB0EG7FzoXDEYixUd8mhm8iAZ ADBj+2rH9uqNhafd5ooq9rw2YUKygbNLWdjBFpCh8Q1z8YJFDtAtGhiZUAVZbA/qSrmK b1uVZjl1m1shH5/aoi6iq0wDVMxmVeZXTcj7l6iZk7BjGcLsdh6IZHHPIL2v1xIGCB9s cWOcnvlG3JB6lxWGtr1qPN7j9NtCqnzUFQboST78ejKExjqQV4d9y8p5om3aSBzZX07k a0GA== X-Gm-Message-State: ANhLgQ1A1Eo6aVJp7FrZ1jYsAD06n741BBOoU8covk/i2KMlF22qh+gF /AW8+INQnAX4GiyrH9FfFCsoqQ== 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-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@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