Re: mmots test error: WARNING in __wake_up_common

[Dmitry Vyukov]

On Fri, Dec 1, 2017 at 2:23 PM, syzbot
<bot+8a9655dff1b0463b1f5eb8f45a81d652d08d428b@xxxxxxxxxxxxxxxxxxxxxxxxx>
wrote:
> Hello,
>
> syzkaller hit the following crash on
> 11f44eb001da4c07b80055d8e24a0db4fb47eab1
> git://git.cmpxchg.org/linux-mmots.git/master
> compiler: gcc (GCC) 7.1.1 20170620
> .config is attached
> Raw console output is attached.
>
> Unfortunately, I don't have any reproducer for this bug yet.
>
>
> WARNING: CPU: 1 PID: 3084 at kernel/sched/wait.c:79
> __wake_up_common+0x433/0x770 kernel/sched/wait.c:79
> Kernel panic - not syncing: panic_on_warn set ...
>
> CPU: 1 PID: 3084 Comm: syz-fuzzer Not tainted 4.15.0-rc1-mm1+ #32
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
> Google 01/01/2011
> Call Trace:
>  __dump_stack lib/dump_stack.c:17 [inline]
>  dump_stack+0x194/0x257 lib/dump_stack.c:53
>  panic+0x1e4/0x41c kernel/panic.c:183
>  __warn+0x1dc/0x200 kernel/panic.c:547
>  report_bug+0x211/0x2d0 lib/bug.c:184
>  fixup_bug.part.11+0x37/0x80 arch/x86/kernel/traps.c:177
>  fixup_bug arch/x86/kernel/traps.c:246 [inline]
>  do_error_trap+0x2d7/0x3e0 arch/x86/kernel/traps.c:295
>  do_invalid_op+0x1b/0x20 arch/x86/kernel/traps.c:314
>  invalid_op+0x22/0x40 arch/x86/entry/entry_64.S:1066
> RIP: 0010:__wake_up_common+0x433/0x770 kernel/sched/wait.c:79
> RSP: 0018:ffff8801cb6874b0 EFLAGS: 00010046
> RAX: 0000000000000000 RBX: ffff8801cc87e8d0 RCX: 0000000000000004
> RDX: 1ffffffff0bd9741 RSI: ffff8801cc87e8e8 RDI: 0000000000000082
> RBP: ffff8801cb6875b0 R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000000 R11: ffffffff8748cda0 R12: 0000000000000000
> R13: ffff8801cc87e910 R14: 0000000000000001 R15: ffff8801cc87e970
>  __wake_up_locked+0x11/0x20 kernel/sched/wait.c:160
>  ep_insert+0x15d0/0x1b10 fs/eventpoll.c:1495
>  SYSC_epoll_ctl fs/eventpoll.c:2106 [inline]
>  SyS_epoll_ctl+0x12e4/0x1ab0 fs/eventpoll.c:1992
>  entry_SYSCALL_64_fastpath+0x1f/0x96
> RIP: 0033:0x45f7d8
> RSP: 002b:000000c4203e5300 EFLAGS: 00000246 ORIG_RAX: 00000000000000e9
> RAX: ffffffffffffffda RBX: 000000c42008c140 RCX: 000000000045f7d8
> RDX: 0000000000000007 RSI: 0000000000000001 RDI: 0000000000000004
> RBP: 000000c4203e56b8 R08: 0000000000000000 R09: 0000000000000000
> R10: 000000c4203e532c R11: 0000000000000246 R12: 0000000000000000
> R13: 00000000000000f2 R14: 0000000000000032 R15: 000000000000000f
> Dumping ftrace buffer:
>    (ftrace buffer empty)
> Kernel Offset: disabled
> Rebooting in 86400 seconds..


I see there was a very recent commit in mm tree that touches this code:

commit f71569128519ba77d0bfb6a5a1f1c575804a2970
Author: Christoph Hellwig <hch@xxxxxx>
Date:   Fri Dec 1 00:01:01 2017 +0000
    epoll: use proper wake_up variant in ep_poll_callback

This was triggered when we just ssh into the instance.


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