linux-kernel - Re: [syzbot] KCSAN: data-race in call_rcu / rcu_gp_fqs

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Date:   Mon, 25 Oct 2021 12:31:53 +0200
From:   Marco Elver <elver@...gle.com>
To:     syzbot <syzbot+4dfb96a94317a78f44d9@...kaller.appspotmail.com>,
        "Paul E. McKenney" <paulmck@...nel.org>, rcu@...r.kernel.org
Cc:     linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        syzkaller-bugs@...glegroups.com, viro@...iv.linux.org.uk
Subject: Re: [syzbot] KCSAN: data-race in call_rcu / rcu_gp_fqs_loop

+Cc Paul

data race is in rcu code, presumably not yet discovered by rcutorture?

On Mon, 25 Oct 2021 at 12:29, syzbot
<syzbot+4dfb96a94317a78f44d9@...kaller.appspotmail.com> wrote:
>
> Hello,
>
> syzbot found the following issue on:
>
> HEAD commit:    9c0c4d24ac00 Merge tag 'block-5.15-2021-10-22' of git://gi..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=159c4954b00000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=6339b6ea86d89fd7
> dashboard link: https://syzkaller.appspot.com/bug?extid=4dfb96a94317a78f44d9
> compiler:       Debian clang version 11.0.1-2, GNU ld (GNU Binutils for Debian) 2.35.2
>
> 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+4dfb96a94317a78f44d9@...kaller.appspotmail.com
>
> ==================================================================
> BUG: KCSAN: data-race in call_rcu / rcu_gp_fqs_loop
>
> write to 0xffffffff837342e0 of 8 bytes by task 11 on cpu 1:
>  rcu_gp_fqs kernel/rcu/tree.c:1910 [inline]
>  rcu_gp_fqs_loop+0x348/0x470 kernel/rcu/tree.c:1971
>  rcu_gp_kthread+0x25/0x1a0 kernel/rcu/tree.c:2130
>  kthread+0x262/0x280 kernel/kthread.c:319
>  ret_from_fork+0x1f/0x30
>
> read to 0xffffffff837342e0 of 8 bytes by task 379 on cpu 0:
>  __call_rcu_core kernel/rcu/tree.c:2904 [inline]
>  __call_rcu kernel/rcu/tree.c:3020 [inline]
>  call_rcu+0x4c0/0x6d0 kernel/rcu/tree.c:3067
>  __dentry_kill+0x3ec/0x4e0 fs/dcache.c:596
>  dput+0xc6/0x360 fs/dcache.c:888
>  do_unlinkat+0x2a8/0x540 fs/namei.c:4172
>  __do_sys_unlink fs/namei.c:4217 [inline]
>  __se_sys_unlink fs/namei.c:4215 [inline]
>  __x64_sys_unlink+0x2c/0x30 fs/namei.c:4215
>  do_syscall_x64 arch/x86/entry/common.c:50 [inline]
>  do_syscall_64+0x44/0xa0 arch/x86/entry/common.c:80
>  entry_SYSCALL_64_after_hwframe+0x44/0xae
>
> value changed: 0x0000000000005c0d -> 0x0000000000005c0e
>
> Reported by Kernel Concurrency Sanitizer on:
> CPU: 0 PID: 379 Comm: udevd Tainted: G        W         5.15.0-rc6-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@...glegroups.com.
>
> syzbot will keep track of this issue. See:
> https://goo.gl/tpsmEJ#status for how to communicate with syzbot.