Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
MIME-Version: 1.0
References: <000000000000411e4b059683a39c@google.com>
In-Reply-To: <000000000000411e4b059683a39c@google.com>
From:   Marco Elver <elver@google.com>
Date:   Mon, 4 Nov 2019 12:32:57 +0100
Message-ID: <CANpmjNMegMA6d5n1cV5JLmMbbe-3TkH5q3sNt9+E+wb8esjvoA@mail.gmail.com>
Subject: Re: KCSAN: data-race in __rcu_read_unlock / sync_rcu_exp_select_cpus
To:     syzbot <syzbot+99f4ddade3c22ab0cf23@syzkaller.appspotmail.com>,
        Lai Jiangshan <jiangshanlai@gmail.com>,
        "Paul E. McKenney" <paulmck@kernel.org>,
        Josh Triplett <josh@joshtriplett.org>, rcu@vger.kernel.org
Cc:     Andrew Morton <akpm@linux-foundation.org>, amir73il@gmail.com,
        darrick.wong@oracle.com, Johannes Weiner <hannes@cmpxchg.org>,
        jack@suse.cz, josef@toxicpanda.com,
        LKML <linux-kernel@vger.kernel.org>,
        Linux Memory Management List <linux-mm@kvack.org>,
        songliubraving@fb.com, syzkaller-bugs@googlegroups.com,
        willy@infradead.org
Content-Type: text/plain; charset="UTF-8"
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

+RCU folks

On Mon, 4 Nov 2019 at 12:30, syzbot
<syzbot+99f4ddade3c22ab0cf23@syzkaller.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=1296ff50e00000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=87d111955f40591f
> dashboard link: https://syzkaller.appspot.com/bug?extid=99f4ddade3c22ab0cf23
> 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+99f4ddade3c22ab0cf23@syzkaller.appspotmail.com
>
> ==================================================================
> BUG: KCSAN: data-race in __rcu_read_unlock / sync_rcu_exp_select_cpus
>
> read to 0xffffffff85a7d440 of 8 bytes by task 7624 on cpu 0:
>   rcu_read_unlock_special kernel/rcu/tree_plugin.h:615 [inline]
>   __rcu_read_unlock+0x381/0x3c0 kernel/rcu/tree_plugin.h:383
>   rcu_read_unlock include/linux/rcupdate.h:652 [inline]
>   filemap_map_pages+0x5b3/0x990 mm/filemap.c:2687
>   do_fault_around mm/memory.c:3450 [inline]
>   do_read_fault mm/memory.c:3484 [inline]
>   do_fault mm/memory.c:3618 [inline]
>   handle_pte_fault mm/memory.c:3849 [inline]
>   __handle_mm_fault+0x2554/0x2cb0 mm/memory.c:3973
>   handle_mm_fault+0x21b/0x530 mm/memory.c:4010
>   do_user_addr_fault arch/x86/mm/fault.c:1441 [inline]
>   __do_page_fault+0x3fb/0x9e0 arch/x86/mm/fault.c:1506
>   do_page_fault+0x54/0x233 arch/x86/mm/fault.c:1530
>   page_fault+0x34/0x40 arch/x86/entry/entry_64.S:1202
>
> write to 0xffffffff85a7d440 of 8 bytes by task 7353 on cpu 1:
>   sync_exp_reset_tree kernel/rcu/tree_exp.h:137 [inline]
>   sync_rcu_exp_select_cpus+0xd5/0x590 kernel/rcu/tree_exp.h:427
>   rcu_exp_sel_wait_wake kernel/rcu/tree_exp.h:575 [inline]
>   wait_rcu_exp_gp+0x25/0x40 kernel/rcu/tree_exp.h:589
>   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: 1 PID: 7353 Comm: kworker/1:0 Not tainted 5.4.0-rc3+ #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
> Google 01/01/2011
> Workqueue: rcu_gp wait_rcu_exp_gp
> ==================================================================
> Kernel panic - not syncing: panic_on_warn set ...
> CPU: 1 PID: 7353 Comm: kworker/1:0 Not tainted 5.4.0-rc3+ #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
> Google 01/01/2011
> Workqueue: rcu_gp wait_rcu_exp_gp
> 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_write8 kernel/kcsan/kcsan.c:36 [inline]
>   __tsan_write8+0x32/0x40 kernel/kcsan/kcsan.c:36
>   sync_exp_reset_tree kernel/rcu/tree_exp.h:137 [inline]
>   sync_rcu_exp_select_cpus+0xd5/0x590 kernel/rcu/tree_exp.h:427
>   rcu_exp_sel_wait_wake kernel/rcu/tree_exp.h:575 [inline]
>   wait_rcu_exp_gp+0x25/0x40 kernel/rcu/tree_exp.h:589
>   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
> Shutting down cpus with NMI
> 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@googlegroups.com.
>
> syzbot will keep track of this bug report. See:
> https://goo.gl/tpsmEJ#status for how to communicate with syzbot.