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Date:   Tue, 6 Apr 2021 21:27:48 +0800
From:   Hao Sun <sunhao.th@...il.com>
To:     Jan Kara <jack@...e.cz>
Cc:     tytso@....edu, jack@...e.com, linux-ext4@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: KCSAN: data-race in __jbd2_journal_file_buffer / jbd2_journal_dirty_metadata

> 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.
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?

Hao

Jan Kara <jack@...e.cz> 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 <jack@...e.com>
> SUSE Labs, CR

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