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=-8.3 required=3.0 tests=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 CDB46C3567B for ; Mon, 24 Feb 2020 09:11:32 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id AC77520836 for ; Mon, 24 Feb 2020 09:11:32 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728463AbgBXJLb (ORCPT ); Mon, 24 Feb 2020 04:11:31 -0500 Received: from mx2.suse.de ([195.135.220.15]:42758 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728355AbgBXJKw (ORCPT ); Mon, 24 Feb 2020 04:10:52 -0500 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx2.suse.de (Postfix) with ESMTP id 7C1D9AC92; Mon, 24 Feb 2020 09:10:50 +0000 (UTC) Received: by quack2.suse.cz (Postfix, from userid 1000) id 6BBFA1E0E33; Mon, 24 Feb 2020 10:10:51 +0100 (CET) Date: Mon, 24 Feb 2020 10:10:51 +0100 From: Jan Kara To: Qian Cai Cc: tytso@mit.edu, jack@suse.com, linux-ext4@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] fs/jbd2: fix data races at struct journal_head Message-ID: <20200224091051.GC27857@quack2.suse.cz> References: <20200222043111.2227-1-cai@lca.pw> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200222043111.2227-1-cai@lca.pw> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri 21-02-20 23:31:11, Qian Cai wrote: > journal_head::b_transaction and journal_head::b_next_transaction could > be accessed concurrently as noticed by KCSAN, > > LTP: starting fsync04 > /dev/zero: Can't open blockdev > EXT4-fs (loop0): mounting ext3 file system using the ext4 subsystem > EXT4-fs (loop0): mounted filesystem with ordered data mode. Opts: (null) > ================================================================== > BUG: KCSAN: data-race in __jbd2_journal_refile_buffer [jbd2] / jbd2_write_access_granted [jbd2] > > write to 0xffff99f9b1bd0e30 of 8 bytes by task 25721 on cpu 70: > __jbd2_journal_refile_buffer+0xdd/0x210 [jbd2] > __jbd2_journal_refile_buffer at fs/jbd2/transaction.c:2569 > jbd2_journal_commit_transaction+0x2d15/0x3f20 [jbd2] > (inlined by) jbd2_journal_commit_transaction at fs/jbd2/commit.c:1034 > kjournald2+0x13b/0x450 [jbd2] > kthread+0x1cd/0x1f0 > ret_from_fork+0x27/0x50 > > read to 0xffff99f9b1bd0e30 of 8 bytes by task 25724 on cpu 68: > jbd2_write_access_granted+0x1b2/0x250 [jbd2] > jbd2_write_access_granted at fs/jbd2/transaction.c:1155 > jbd2_journal_get_write_access+0x2c/0x60 [jbd2] > __ext4_journal_get_write_access+0x50/0x90 [ext4] > ext4_mb_mark_diskspace_used+0x158/0x620 [ext4] > ext4_mb_new_blocks+0x54f/0xca0 [ext4] > ext4_ind_map_blocks+0xc79/0x1b40 [ext4] > ext4_map_blocks+0x3b4/0x950 [ext4] > _ext4_get_block+0xfc/0x270 [ext4] > ext4_get_block+0x3b/0x50 [ext4] > __block_write_begin_int+0x22e/0xae0 > __block_write_begin+0x39/0x50 > ext4_write_begin+0x388/0xb50 [ext4] > generic_perform_write+0x15d/0x290 > ext4_buffered_write_iter+0x11f/0x210 [ext4] > ext4_file_write_iter+0xce/0x9e0 [ext4] > new_sync_write+0x29c/0x3b0 > __vfs_write+0x92/0xa0 > vfs_write+0x103/0x260 > ksys_write+0x9d/0x130 > __x64_sys_write+0x4c/0x60 > do_syscall_64+0x91/0xb05 > entry_SYSCALL_64_after_hwframe+0x49/0xbe > > 5 locks held by fsync04/25724: > #0: ffff99f9911093f8 (sb_writers#13){.+.+}, at: vfs_write+0x21c/0x260 > #1: ffff99f9db4c0348 (&sb->s_type->i_mutex_key#15){+.+.}, at: ext4_buffered_write_iter+0x65/0x210 [ext4] > #2: ffff99f5e7dfcf58 (jbd2_handle){++++}, at: start_this_handle+0x1c1/0x9d0 [jbd2] > #3: ffff99f9db4c0168 (&ei->i_data_sem){++++}, at: ext4_map_blocks+0x176/0x950 [ext4] > #4: ffffffff99086b40 (rcu_read_lock){....}, at: jbd2_write_access_granted+0x4e/0x250 [jbd2] > irq event stamp: 1407125 > hardirqs last enabled at (1407125): [] __find_get_block+0x107/0x790 > hardirqs last disabled at (1407124): [] __find_get_block+0x49/0x790 > softirqs last enabled at (1405528): [] __do_softirq+0x34c/0x57c > softirqs last disabled at (1405521): [] irq_exit+0xa2/0xc0 > > Reported by Kernel Concurrency Sanitizer on: > CPU: 68 PID: 25724 Comm: fsync04 Tainted: G L 5.6.0-rc2-next-20200221+ #7 > Hardware name: HPE ProLiant DL385 Gen10/ProLiant DL385 Gen10, BIOS A40 07/10/2019 > > The plain reads are outside of jh->b_state_lock critical section which result > in data races. Fix them by adding pairs of READ|WRITE_ONCE(). > > Signed-off-by: Qian Cai Yeah, makes sense. You can add: Reviewed-by: Jan Kara Honza > --- > fs/jbd2/transaction.c | 8 ++++---- > 1 file changed, 4 insertions(+), 4 deletions(-) > > diff --git a/fs/jbd2/transaction.c b/fs/jbd2/transaction.c > index 2dd848a743ed..c5f7f6d0f33b 100644 > --- a/fs/jbd2/transaction.c > +++ b/fs/jbd2/transaction.c > @@ -1152,8 +1152,8 @@ static bool jbd2_write_access_granted(handle_t *handle, struct buffer_head *bh, > /* For undo access buffer must have data copied */ > if (undo && !jh->b_committed_data) > goto out; > - if (jh->b_transaction != handle->h_transaction && > - jh->b_next_transaction != handle->h_transaction) > + if (READ_ONCE(jh->b_transaction) != handle->h_transaction && > + READ_ONCE(jh->b_next_transaction) != handle->h_transaction) > goto out; > /* > * There are two reasons for the barrier here: > @@ -2565,8 +2565,8 @@ bool __jbd2_journal_refile_buffer(struct journal_head *jh) > * our jh reference and thus __jbd2_journal_file_buffer() must not > * take a new one. > */ > - jh->b_transaction = jh->b_next_transaction; > - jh->b_next_transaction = NULL; > + WRITE_ONCE(jh->b_transaction, jh->b_next_transaction); > + WRITE_ONCE(jh->b_next_transaction, NULL); > if (buffer_freed(bh)) > jlist = BJ_Forget; > else if (jh->b_modified) > -- > 2.21.0 (Apple Git-122.2) > -- Jan Kara SUSE Labs, CR