Re: [syzbot] KCSAN: data-race in call_rcu / rcu_gp_kthread

[Marco Elver]

[-Bcc: fsdevel]
[+Cc: Paul, rcu@xxxxxxxxxxxxxxx]

On Mon, 12 Jul 2021 at 18:09, syzbot
<syzbot+e08a83a1940ec3846cd5@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote:
>
> Hello,
>
> syzbot found the following issue on:
>
> HEAD commit:    e73f0f0e Linux 5.14-rc1
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=172196d2300000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=f5e73542d774430b
> dashboard link: https://syzkaller.appspot.com/bug?extid=e08a83a1940ec3846cd5
> 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+e08a83a1940ec3846cd5@xxxxxxxxxxxxxxxxxxxxxxxxx
>
> ==================================================================
> BUG: KCSAN: data-race in call_rcu / rcu_gp_kthread
>
> write to 0xffffffff837328a0 of 8 bytes by task 11 on cpu 0:
>  rcu_gp_fqs kernel/rcu/tree.c:1949 [inline]
>  rcu_gp_fqs_loop kernel/rcu/tree.c:2010 [inline]
>  rcu_gp_kthread+0xd78/0xec0 kernel/rcu/tree.c:2169
>  kthread+0x262/0x280 kernel/kthread.c:319
>  ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295
>
> read to 0xffffffff837328a0 of 8 bytes by task 30193 on cpu 1:
>  __call_rcu_core kernel/rcu/tree.c:2946 [inline]
>  __call_rcu kernel/rcu/tree.c:3062 [inline]
>  call_rcu+0x4b0/0x6c0 kernel/rcu/tree.c:3109
>  file_free fs/file_table.c:58 [inline]
>  __fput+0x43e/0x4e0 fs/file_table.c:298
>  ____fput+0x11/0x20 fs/file_table.c:313
>  task_work_run+0xae/0x130 kernel/task_work.c:164
>  get_signal+0x156c/0x15e0 kernel/signal.c:2581
>  arch_do_signal_or_restart+0x2a/0x220 arch/x86/kernel/signal.c:865
>  handle_signal_work kernel/entry/common.c:148 [inline]
>  exit_to_user_mode_loop kernel/entry/common.c:172 [inline]
>  exit_to_user_mode_prepare+0x109/0x190 kernel/entry/common.c:209
>  __syscall_exit_to_user_mode_work kernel/entry/common.c:291 [inline]
>  syscall_exit_to_user_mode+0x20/0x40 kernel/entry/common.c:302
>  do_syscall_64+0x49/0x90 arch/x86/entry/common.c:86
>  entry_SYSCALL_64_after_hwframe+0x44/0xae
>
> value changed: 0x0000000000000f57 -> 0x0000000000000f58
>
> Reported by Kernel Concurrency Sanitizer on:
> CPU: 1 PID: 30193 Comm: syz-executor.5 Tainted: G        W         5.14.0-rc1-syzkaller #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
> ==================================================================
>
>
> ---
> This report is generated by a bot. It may contain errors.
> See https://goo.gl/tpsmEJ for more information about syzbot.
> syzbot engineers can be reached at syzkaller@xxxxxxxxxxxxxxxx.
>
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>
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