linux-kernel - Re: KCSAN: data-race in process_srcu / synchronize

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Date:   Mon, 4 Nov 2019 12:31:56 +0100
From:   Marco Elver <elver@...gle.com>
To:     syzbot <syzbot+08f3e9d26e5541e1ecf2@...kaller.appspotmail.com>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Josh Triplett <josh@...htriplett.org>
Cc:     axboe@...nel.dk, justin@...aid.com, linux-block@...r.kernel.org,
        LKML <linux-kernel@...r.kernel.org>,
        syzkaller-bugs@...glegroups.com
Subject: Re: KCSAN: data-race in process_srcu / synchronize_srcu

+RCU folks, since this is probably a data race in RCU.

On Mon, 4 Nov 2019 at 12:29, syzbot
<syzbot+08f3e9d26e5541e1ecf2@...kaller.appspotmail.com> wrote:
>
> Hello,
>
> syzbot found the following crash on:
>
> HEAD commit:    05f22368 x86, kcsan: Enable KCSAN for x86
> git tree:       https://github.com/google/ktsan.git kcsan
> console output: https://syzkaller.appspot.com/x/log.txt?x=17ade7ef600000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=87d111955f40591f
> dashboard link: https://syzkaller.appspot.com/bug?extid=08f3e9d26e5541e1ecf2
> compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
>
> Unfortunately, I don't have any reproducer for this crash yet.
>
> IMPORTANT: if you fix the bug, please add the following tag to the commit:
> Reported-by: syzbot+08f3e9d26e5541e1ecf2@...kaller.appspotmail.com
>
> ==================================================================
> BUG: KCSAN: data-race in process_srcu / synchronize_srcu
>
> write to 0xffffffff8604e8a0 of 8 bytes by task 17 on cpu 1:
>   srcu_gp_end kernel/rcu/srcutree.c:533 [inline]
>   srcu_advance_state kernel/rcu/srcutree.c:1146 [inline]
>   process_srcu+0x207/0x780 kernel/rcu/srcutree.c:1237
>   process_one_work+0x3d4/0x890 kernel/workqueue.c:2269
>   worker_thread+0xa0/0x800 kernel/workqueue.c:2415
>   kthread+0x1d4/0x200 drivers/block/aoe/aoecmd.c:1253
>   ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:352
>
> read to 0xffffffff8604e8a0 of 8 bytes by task 12515 on cpu 0:
>   srcu_might_be_idle kernel/rcu/srcutree.c:784 [inline]
>   synchronize_srcu+0x107/0x214 kernel/rcu/srcutree.c:996
>   fsnotify_connector_destroy_workfn+0x63/0xb0 fs/notify/mark.c:164
>   process_one_work+0x3d4/0x890 kernel/workqueue.c:2269
>   worker_thread+0xa0/0x800 kernel/workqueue.c:2415
>   kthread+0x1d4/0x200 drivers/block/aoe/aoecmd.c:1253
>   ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:352
>
> Reported by Kernel Concurrency Sanitizer on:
> CPU: 0 PID: 12515 Comm: kworker/u4:8 Not tainted 5.4.0-rc3+ #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
> Google 01/01/2011
> Workqueue: events_unbound fsnotify_connector_destroy_workfn
> ==================================================================
> Kernel panic - not syncing: panic_on_warn set ...
> CPU: 0 PID: 12515 Comm: kworker/u4:8 Not tainted 5.4.0-rc3+ #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
> Google 01/01/2011
> Workqueue: events_unbound fsnotify_connector_destroy_workfn
> Call Trace:
>   __dump_stack lib/dump_stack.c:77 [inline]
>   dump_stack+0xf5/0x159 lib/dump_stack.c:113
>   panic+0x210/0x640 kernel/panic.c:221
>   kcsan_report.cold+0xc/0x10 kernel/kcsan/report.c:302
>   __kcsan_setup_watchpoint+0x32e/0x4a0 kernel/kcsan/core.c:411
>   __tsan_read8 kernel/kcsan/kcsan.c:36 [inline]
>   __tsan_read8+0x2c/0x30 kernel/kcsan/kcsan.c:36
>   srcu_might_be_idle kernel/rcu/srcutree.c:784 [inline]
>   synchronize_srcu+0x107/0x214 kernel/rcu/srcutree.c:996
>   fsnotify_connector_destroy_workfn+0x63/0xb0 fs/notify/mark.c:164
>   process_one_work+0x3d4/0x890 kernel/workqueue.c:2269
>   worker_thread+0xa0/0x800 kernel/workqueue.c:2415
>   kthread+0x1d4/0x200 drivers/block/aoe/aoecmd.c:1253
>   ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:352
> Kernel Offset: disabled
> Rebooting in 86400 seconds..
>
>
> ---
> This bug 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 bug report. See:
> https://goo.gl/tpsmEJ#status for how to communicate with syzbot.