netdev - Re: WARNING in kcm_exit

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Date:   Thu, 31 May 2018 12:58:56 +0300
From:   Kirill Tkhai <ktkhai@...tuozzo.com>
To:     syzbot <syzbot+5f1a04e374a635efc426@...kaller.appspotmail.com>,
        davem@...emloft.net, ebiggers@...gle.com, edumazet@...gle.com,
        linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
        syzkaller-bugs@...glegroups.com, tom@...ntonium.net,
        viro@...IV.linux.org.uk
Subject: Re: WARNING in kcm_exit_net (3)

On 31.05.2018 11:16, syzbot wrote:
> Hello,
> 
> syzbot found the following crash on:
> 
> HEAD commit:    d60d61f36b8f Merge branch 'for-linus' of git://git.kernel...
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=101bb52f800000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=968b0b23c7854c0b
> dashboard link: https://syzkaller.appspot.com/bug?extid=5f1a04e374a635efc426
> compiler:       gcc (GCC) 8.0.1 20180413 (experimental)
> syzkaller repro:https://syzkaller.appspot.com/x/repro.syz?x=13b9ed2f800000
> 
> IMPORTANT: if you fix the bug, please add the following tag to the commit:
> Reported-by: syzbot+5f1a04e374a635efc426@...kaller.appspotmail.com
> 
> IPVS: ftp: loaded support on port[0] = 21
> IPVS: ftp: loaded support on port[0] = 21
> IPVS: ftp: loaded support on port[0] = 21
> IPVS: ftp: loaded support on port[0] = 21
> IPVS: ftp: loaded support on port[0] = 21
> WARNING: CPU: 0 PID: 6 at net/kcm/kcmsock.c:2023 kcm_exit_net+0x392/0x3e0 net/kcm/kcmsock.c:2023

Hm, there is allocated a kernel socket in kcm_clone(). It does not get net counter
and it seems kcm_done_work() may complete after kcm_exit_net() is completed. So,
it looks like we have to flush work queue in kcm_exit_net().

> Kernel panic - not syncing: panic_on_warn set ...
> 
> CPU: 0 PID: 6 Comm: kworker/u4:0 Not tainted 4.17.0-rc7+ #75
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
> Workqueue: netns cleanup_net
> Call Trace:
>  __dump_stack lib/dump_stack.c:77 [inline]
>  dump_stack+0x1b9/0x294 lib/dump_stack.c:113
>  panic+0x22f/0x4de kernel/panic.c:184
>  __warn.cold.8+0x163/0x1b3 kernel/panic.c:536
>  report_bug+0x252/0x2d0 lib/bug.c:186
>  fixup_bug arch/x86/kernel/traps.c:178 [inline]
>  do_error_trap+0x1de/0x490 arch/x86/kernel/traps.c:296
>  do_invalid_op+0x1b/0x20 arch/x86/kernel/traps.c:315
>  invalid_op+0x14/0x20 arch/x86/entry/entry_64.S:992
> RIP: 0010:kcm_exit_net+0x392/0x3e0 net/kcm/kcmsock.c:2023
> RSP: 0018:ffff8801d9a97430 EFLAGS: 00010293
> RAX: ffff8801d9a88180 RBX: 1ffff1003b352e86 RCX: 1ffff1003b351135
> RDX: 0000000000000000 RSI: ffffffff86d56942 RDI: 0000000000000286
> RBP: ffff8801d9a974f8 R08: 1ffff1003b352e67 R09: ffffed003b5c46d2
> R10: 0000000000000003 R11: 0000000000000003 R12: 1ffff1003b352e8a
> R13: ffff8801d9a974d0 R14: ffff8801d96763d0 R15: ffff8801c51d0e00
>  ops_exit_list.isra.7+0xb0/0x160 net/core/net_namespace.c:152
>  cleanup_net+0x51d/0xb20 net/core/net_namespace.c:523
>  process_one_work+0xc1e/0x1b50 kernel/workqueue.c:2145
>  worker_thread+0x1cc/0x1440 kernel/workqueue.c:2279
>  kthread+0x345/0x410 kernel/kthread.c:240
>  ret_from_fork+0x3a/0x50 arch/x86/entry/entry_64.S:412
> Dumping ftrace buffer:
>    (ftrace buffer empty)
> 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#bug-status-tracking for how to communicate with syzbot.
> syzbot can test patches for this bug, for details see:
> https://goo.gl/tpsmEJ#testing-patches