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=-10.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,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 0F09EC433E0 for ; Thu, 11 Mar 2021 14:26:03 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id C23FB64FC3 for ; Thu, 11 Mar 2021 14:26:02 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233368AbhCKOZe (ORCPT ); Thu, 11 Mar 2021 09:25:34 -0500 Received: from mx2.suse.de ([195.135.220.15]:49540 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233254AbhCKOZG (ORCPT ); Thu, 11 Mar 2021 09:25:06 -0500 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 A8368AC8C; Thu, 11 Mar 2021 14:25:04 +0000 (UTC) Received: by quack2.suse.cz (Postfix, from userid 1000) id 3DFEA1F2BD9; Thu, 11 Mar 2021 15:25:03 +0100 (CET) Date: Thu, 11 Mar 2021 15:25:03 +0100 From: Jan Kara To: syzbot Cc: jack@suse.com, linux-ext4@vger.kernel.org, linux-kernel@vger.kernel.org, syzkaller-bugs@googlegroups.com, tytso@mit.edu Subject: Re: [syzbot] KCSAN: data-race in start_this_handle / start_this_handle Message-ID: <20210311142503.GA31816@quack2.suse.cz> References: <0000000000008de88005bd40ac36@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <0000000000008de88005bd40ac36@google.com> User-Agent: Mutt/1.10.1 (2018-07-13) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu 11-03-21 02:59:14, syzbot wrote: > HEAD commit: a74e6a01 Merge tag 's390-5.12-3' of git://git.kernel.org/p.. > git tree: upstream > console output: https://syzkaller.appspot.com/x/log.txt?x=159f69ecd00000 > kernel config: https://syzkaller.appspot.com/x/.config?x=de394bbaade74fb7 > dashboard link: https://syzkaller.appspot.com/bug?extid=30774a6acf6a2cf6d535 > compiler: Debian clang version 11.0.1-2 > > Unfortunately, I don't have any reproducer for this issue yet. > > IMPORTANT: if you fix the issue, please add the following tag to the commit: > Reported-by: syzbot+30774a6acf6a2cf6d535@syzkaller.appspotmail.com > > ================================================================== > BUG: KCSAN: data-race in start_this_handle / start_this_handle > > write to 0xffff888103880870 of 8 bytes by task 29956 on cpu 1: > jbd2_get_transaction fs/jbd2/transaction.c:125 [inline] > start_this_handle+0xceb/0x1010 fs/jbd2/transaction.c:400 > jbd2__journal_start+0x1fc/0x3f0 fs/jbd2/transaction.c:503 > __ext4_journal_start_sb+0x159/0x310 fs/ext4/ext4_jbd2.c:105 > __ext4_journal_start fs/ext4/ext4_jbd2.h:320 [inline] > ext4_da_write_begin+0x460/0xaf0 fs/ext4/inode.c:2998 > generic_perform_write+0x196/0x3a0 mm/filemap.c:3575 > ext4_buffered_write_iter+0x2e5/0x3e0 fs/ext4/file.c:269 > ext4_file_write_iter+0x48a/0x10b0 fs/ext4/file.c:502 > call_write_iter include/linux/fs.h:1977 [inline] > do_iter_readv_writev+0x2cb/0x360 fs/read_write.c:740 > do_iter_write+0x112/0x4c0 fs/read_write.c:866 > vfs_iter_write+0x4c/0x70 fs/read_write.c:907 > iter_file_splice_write+0x40a/0x750 fs/splice.c:689 > do_splice_from fs/splice.c:767 [inline] > direct_splice_actor+0x80/0xa0 fs/splice.c:936 > splice_direct_to_actor+0x345/0x650 fs/splice.c:891 > do_splice_direct+0xf5/0x170 fs/splice.c:979 > do_sendfile+0x7a6/0xe20 fs/read_write.c:1260 > __do_sys_sendfile64 fs/read_write.c:1319 [inline] > __se_sys_sendfile64 fs/read_write.c:1311 [inline] > __x64_sys_sendfile64+0xa9/0x130 fs/read_write.c:1311 > do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46 > entry_SYSCALL_64_after_hwframe+0x44/0xae > > read to 0xffff888103880870 of 8 bytes by task 29936 on cpu 0: > start_this_handle+0x1c1/0x1010 fs/jbd2/transaction.c:352 > jbd2__journal_start+0x1fc/0x3f0 fs/jbd2/transaction.c:503 > __ext4_journal_start_sb+0x159/0x310 fs/ext4/ext4_jbd2.c:105 > __ext4_journal_start fs/ext4/ext4_jbd2.h:320 [inline] > ext4_da_write_begin+0x460/0xaf0 fs/ext4/inode.c:2998 > generic_perform_write+0x196/0x3a0 mm/filemap.c:3575 > ext4_buffered_write_iter+0x2e5/0x3e0 fs/ext4/file.c:269 > ext4_file_write_iter+0x48a/0x10b0 fs/ext4/file.c:502 > call_write_iter include/linux/fs.h:1977 [inline] > do_iter_readv_writev+0x2cb/0x360 fs/read_write.c:740 > do_iter_write+0x112/0x4c0 fs/read_write.c:866 > vfs_iter_write+0x4c/0x70 fs/read_write.c:907 > iter_file_splice_write+0x40a/0x750 fs/splice.c:689 > do_splice_from fs/splice.c:767 [inline] > direct_splice_actor+0x80/0xa0 fs/splice.c:936 > splice_direct_to_actor+0x345/0x650 fs/splice.c:891 > do_splice_direct+0xf5/0x170 fs/splice.c:979 > do_sendfile+0x7a6/0xe20 fs/read_write.c:1260 > __do_sys_sendfile64 fs/read_write.c:1319 [inline] > __se_sys_sendfile64 fs/read_write.c:1311 [inline] > __x64_sys_sendfile64+0xa9/0x130 fs/read_write.c:1311 > do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46 > entry_SYSCALL_64_after_hwframe+0x44/0xae > > Reported by Kernel Concurrency Sanitizer on: > CPU: 0 PID: 29936 Comm: syz-executor.5 Not tainted 5.12.0-rc2-syzkaller #0 > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 > ================================================================== So this case is harmless. start_this_handle() does indeed check journal->j_running_transaction without any protection and this is only a racy check to opportunistically preallocate a transaction if we are likely to need it. There was some macro to instruct KCSAN that the read is actually fine, wasn't there? Honza -- Jan Kara SUSE Labs, CR