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=-10.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING, 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 E4865C433B4 for ; Tue, 6 Apr 2021 14:05:09 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 99F41613A7 for ; Tue, 6 Apr 2021 14:05:09 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1344883AbhDFOFP (ORCPT ); Tue, 6 Apr 2021 10:05:15 -0400 Received: from mx2.suse.de ([195.135.220.15]:34984 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232387AbhDFOFO (ORCPT ); Tue, 6 Apr 2021 10:05:14 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 308EAB0BE; Tue, 6 Apr 2021 14:05:05 +0000 (UTC) Received: by quack2.suse.cz (Postfix, from userid 1000) id EF1711F2B77; Tue, 6 Apr 2021 16:05:04 +0200 (CEST) Date: Tue, 6 Apr 2021 16:05:04 +0200 From: Jan Kara To: Hao Sun Cc: Jan Kara , tytso@mit.edu, jack@suse.com, linux-ext4@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: KCSAN: data-race in __jbd2_journal_file_buffer / jbd2_journal_dirty_metadata Message-ID: <20210406140504.GE19407@quack2.suse.cz> References: <20210406123232.GD19407@quack2.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue 06-04-21 21:27:48, Hao Sun wrote: > > Thanks for report but I'm not sure what KCSAN is complaining about - isn't the report truncated? > > Yes, the full KCSAN report is available in the attached log file. Sorry, I missed that in your original email. > Here is the report : > ================================================================== > BUG: KCSAN: data-race in __jbd2_journal_file_buffer / > jbd2_journal_dirty_metadata > > write to 0xffff88800af6da38 of 8 bytes by task 4822 on cpu 1: > __jbd2_journal_file_buffer+0x18d/0x370 > __jbd2_journal_refile_buffer+0x155/0x230 > jbd2_journal_commit_transaction+0x24c6/0x3200 > kjournald2+0x253/0x470 > kthread+0x1f0/0x220 > ret_from_fork+0x1f/0x30 > > read to 0xffff88800af6da38 of 8 bytes by task 1955 on cpu 0: > jbd2_journal_dirty_metadata+0x17f/0x670 > __ext4_handle_dirty_metadata+0xc6/0x590 > ext4_mark_iloc_dirty+0x12dd/0x16e0 > __ext4_mark_inode_dirty+0x4d2/0x5d0 > ext4_writepages+0x1262/0x1e50 > do_writepages+0x7b/0x150 > __writeback_single_inode+0x84/0x4e0 > writeback_sb_inodes+0x69f/0x1020 > __writeback_inodes_wb+0xb0/0x2a0 > wb_writeback+0x290/0x650 > wb_do_writeback+0x582/0x5d0 > wb_workfn+0xb8/0x410 > process_one_work+0x3e1/0x940 > worker_thread+0x64a/0xaa0 > kthread+0x1f0/0x220 > ret_from_fork+0x1f/0x30 > > Reported by Kernel Concurrency Sanitizer on: > CPU: 0 PID: 1955 Comm: kworker/u5:2 Not tainted 5.11.0+ #5 > > > Sorry, I couldn't symbolize it because the original Linux binary was lost. > Do you think this is an actual bug? So it is difficult to be 100% sure without knowing which particular access caused the KCSAN warning but I'm quite confident it was caused by one of unlocked accesses to jh->b_transaction in jbd2_journal_dirty_metadata(). And as the comments explain, these are only assertions which we redo under proper lock if they look like they would fail. So the code is in fact correct. Honza > Jan Kara 于2021年4月6日周二 下午8:32写道： > > > > Hello! > > > > On Sun 04-04-21 17:40:44, Hao Sun wrote: > > > When using Healer(https://github.com/SunHao-0/healer/tree/dev) to fuzz > > > the Linux kernel, I found a data-race vulnerability in > > > __jbd2_journal_file_buffer / jbd2_journal_dirty_metadata. > > > Sorry, data-race is usually difficult to reproduce. I cannot provide > > > you with a reproducing program. > > > I hope that the call stack information in the crash log can help you > > > locate the problem. > > > Kernel config and full log can be found in the attachment. > > > > > > Here is the detailed information: > > > commit: 3b9cdafb5358eb9f3790de2f728f765fef100731 > > > version: linux 5.11 > > > git tree: upstream > > > report: > > > ================================================================== > > > BUG: KCSAN: data-race in __jbd2_journal_file_buffer / > > > jbd2_journal_dirty_metadata > > > write to 0xffff88800af6da38 of 8 bytes by task 4822 on cpu 1: > > > __jbd2_journal_file_buffer+0x18d/0x370 linux/fs/jbd2/transaction.c:2518 > > > __jbd2_journal_refile_buffer+0x155/0x230 linux/fs/jbd2/transaction.c:2612 > > > jbd2_journal_commit_transaction+0x24c6/0x3200 linux/fs/jbd2/commit.c:1084 > > > kjournald2+0x253/0x470 linux/fs/jbd2/journal.c:213 > > > kthread+0x1f0/0x220 linux/kernel/kthread.c:292 > > > ret_from_fork+0x1f/0x30 linux/arch/x86/entry/entry_64.S:294 > > > > Thanks for report but I'm not sure what KCSAN is complaining about - isn't > > the report truncated? I'm missing 'read' part of the report... The complaint > > is on line: > > > > jh->b_transaction = transaction; > > > > I would guess the complaint is because of the check: > > > > /* > > * This and the following assertions are unreliable since we may see jh > > * in inconsistent state unless we grab bh_state lock. But this is > > * crucial to catch bugs so let's do a reliable check until the > > * lockless handling is fully proven. > > */ > > if (jh->b_transaction != transaction && > > jh->b_next_transaction != transaction) { > > > > And the comment explains, why we do this unreliable check. Again, if we > > wanted to silence KCSAN, we could use data_race() macro but AFAIU Ted isn't > > very fond of that annotation. > > > > Honza > > > > -- > > Jan Kara > > SUSE Labs, CR -- Jan Kara SUSE Labs, CR