On Mon, Oct 07, 2019 at 12:04:16PM +0200, Marco Elver wrote:
> +RCU maintainers
> This might be a data-race in RCU itself.
Quite possibly. I will take a look, but there will be delays due to this
week being bootcamp and all.
Thanx, Paul
> On Mon, 7 Oct 2019 at 12:01, syzbot
> <syzbot+134336b86f728d6e5...@syzkaller.appspotmail.com> wrote:
> >
> > Hello,
> >
> > syzbot found the following crash on:
> >
> > HEAD commit: b4bd9343 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=11edb20d600000
> > kernel config: https://syzkaller.appspot.com/x/.config?x=c0906aa620713d80
> > dashboard link: https://syzkaller.appspot.com/bug?extid=134336b86f728d6e55a0
> > 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+134336b86f728d6e5...@syzkaller.appspotmail.com
> >
> > ==================================================================
> > BUG: KCSAN: data-race in find_next_bit / rcu_report_exp_cpu_mult
> >
> > write to 0xffffffff85a7f140 of 8 bytes by task 7 on cpu 0:
> > rcu_report_exp_cpu_mult+0x4f/0xa0 kernel/rcu/tree_exp.h:244
> > rcu_report_exp_rdp+0x6c/0x90 kernel/rcu/tree_exp.h:254
> > rcu_preempt_deferred_qs_irqrestore+0x3bb/0x580
> > kernel/rcu/tree_plugin.h:475
> > rcu_read_unlock_special+0xec/0x370 kernel/rcu/tree_plugin.h:659
> > __rcu_read_unlock+0xcf/0xe0 kernel/rcu/tree_plugin.h:394
> > rcu_read_unlock include/linux/rcupdate.h:645 [inline]
> > batadv_nc_purge_orig_hash net/batman-adv/network-coding.c:411 [inline]
> > batadv_nc_worker+0x13a/0x390 net/batman-adv/network-coding.c:718
> > 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 0xffffffff85a7f140 of 8 bytes by task 7251 on cpu 1:
> > _find_next_bit lib/find_bit.c:39 [inline]
> > find_next_bit+0x57/0xe0 lib/find_bit.c:70
> > sync_rcu_exp_select_node_cpus+0x28e/0x510 kernel/rcu/tree_exp.h:375
> > sync_rcu_exp_select_cpus+0x30c/0x590 kernel/rcu/tree_exp.h:439
> > 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: 7251 Comm: kworker/1:4 Not tainted 5.3.0+ #0
> > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
> > Google 01/01/2011
> > Workqueue: rcu_gp wait_rcu_exp_gp
> > ==================================================================
> >
> >
> > ---
> > 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 syzkal...@googlegroups.com.
> >
> > syzbot will keep track of this bug report. See:
> > https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
