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=-8.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,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 2CE42C33CA1 for ; Fri, 13 Dec 2019 20:41:06 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 68EFD2477D for ; Fri, 13 Dec 2019 20:41:05 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728947AbfLMTtr (ORCPT ); Fri, 13 Dec 2019 14:49:47 -0500 Received: from mx2.suse.de ([195.135.220.15]:57540 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1728942AbfLMTtq (ORCPT ); Fri, 13 Dec 2019 14:49:46 -0500 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id 76B8EAF65; Fri, 13 Dec 2019 19:49:44 +0000 (UTC) Received: by quack2.suse.cz (Postfix, from userid 1000) id 36FA41E0609; Fri, 13 Dec 2019 20:49:43 +0100 (CET) Date: Fri, 13 Dec 2019 20:49:43 +0100 From: Jan Kara To: Joel Fernandes Cc: Phong Tran , Jan Kara , "Theodore Y. Ts'o" , adilger.kernel@dilger.ca, "Paul E. McKenney" , linux-ext4@vger.kernel.org, LKML , linux-kernel-mentees@lists.linuxfoundation.org, rcu , stable Subject: Re: [PATCH V2] ext4: use rcu API in debug_print_tree Message-ID: <20191213194943.GA959@quack2.suse.cz> References: <20191213113510.GG15474@quack2.suse.cz> <20191213153306.30744-1-tranmanphong@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-ext4-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-ext4@vger.kernel.org On Fri 13-12-19 10:11:50, Joel Fernandes wrote: > On Fri, Dec 13, 2019 at 7:39 AM Phong Tran wrote: > > > > struct ext4_sb_info.system_blks was marked __rcu. > > But access the pointer without using RCU lock and dereference. > > Sparse warning with __rcu notation: > > > > block_validity.c:139:29: warning: incorrect type in argument 1 (different address spaces) > > block_validity.c:139:29: expected struct rb_root const * > > block_validity.c:139:29: got struct rb_root [noderef] * > > > > Reviewed-by: Jan Kara > > Signed-off-by: Phong Tran > > Thanks Phong! Looks like a real bug fix caught thanks to Sparse. So > let us mark for stable as well? Well, not really. The code is active only with CONFIG_EXT4_DEBUG enabled and in this case there's no race with remount (and thus sbi->system_blks changing) possible. So the change is really only to silence the sparse warning. Honza > > - Joel > > > --- > > fs/ext4/block_validity.c | 6 +++++- > > 1 file changed, 5 insertions(+), 1 deletion(-) > > > > --- > > change log: > > V2: Add Reviewed-by: Jan Kara > > > > diff --git a/fs/ext4/block_validity.c b/fs/ext4/block_validity.c > > index d4d4fdfac1a6..1ee04e76bbe0 100644 > > --- a/fs/ext4/block_validity.c > > +++ b/fs/ext4/block_validity.c > > @@ -133,10 +133,13 @@ static void debug_print_tree(struct ext4_sb_info *sbi) > > { > > struct rb_node *node; > > struct ext4_system_zone *entry; > > + struct ext4_system_blocks *system_blks; > > int first = 1; > > > > printk(KERN_INFO "System zones: "); > > - node = rb_first(&sbi->system_blks->root); > > + rcu_read_lock(); > > + system_blks = rcu_dereference(sbi->system_blks); > > + node = rb_first(&system_blks->root); > > while (node) { > > entry = rb_entry(node, struct ext4_system_zone, node); > > printk(KERN_CONT "%s%llu-%llu", first ? "" : ", ", > > @@ -144,6 +147,7 @@ static void debug_print_tree(struct ext4_sb_info *sbi) > > first = 0; > > node = rb_next(node); > > } > > + rcu_read_unlock(); > > printk(KERN_CONT "\n"); > > } > > > > -- > > 2.20.1 > > -- Jan Kara SUSE Labs, CR