Date:   Wed, 20 Dec 2017 00:21:27 +0800
From:   Xin Long <lucien.xin@...il.com>
To:     Dmitry Vyukov <dvyukov@...gle.com>
Cc:     syzbot 
        <bot+21b498fc12cf2041655f8e1eeae0733807d794b3@...kaller.appspotmail.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        syzkaller-bugs@...glegroups.com,
        David Miller <davem@...emloft.net>,
        David Ahern <dsahern@...il.com>,
        Florian Westphal <fw@...len.de>,
        Daniel Borkmann <daniel@...earbox.net>,
        jakub.kicinski@...ronome.com, mschiffer@...verse-factory.net,
        Vladislav Yasevich <vyasevich@...il.com>,
        Jiri Benc <jbenc@...hat.com>, netdev <netdev@...r.kernel.org>
Subject: Re: INFO: task hung in bpf_exit_net

On Tue, Dec 19, 2017 at 8:47 PM, Dmitry Vyukov <dvyukov@...gle.com> wrote:
> On Tue, Dec 19, 2017 at 1:36 PM, syzbot
> <bot+21b498fc12cf2041655f8e1eeae0733807d794b3@...kaller.appspotmail.com>
> wrote:
>> Hello,
>>
>> syzkaller hit the following crash on
>> 7ceb97a071e80f1b5e4cd5a36de135612a836388
>> git://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.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.
>>
>>
>> sctp: sctp_transport_update_pmtu: Reported pmtu 508 too low, using default
>> minimum of 512
>> INFO: task kworker/u4:0:5 blocked for more than 120 seconds.
>>       Not tainted 4.15.0-rc2-next-20171205+ #59
>> "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
>> kworker/u4:0    D15808     5      2 0x80000000
>> Workqueue: netns cleanup_net
>> Call Trace:
>>  context_switch kernel/sched/core.c:2800 [inline]
>>  __schedule+0x8eb/0x2060 kernel/sched/core.c:3376
>>  schedule+0xf5/0x430 kernel/sched/core.c:3435
>>  schedule_preempt_disabled+0x10/0x20 kernel/sched/core.c:3493
>>  __mutex_lock_common kernel/locking/mutex.c:833 [inline]
>>  __mutex_lock+0xaad/0x1a80 kernel/locking/mutex.c:893
>>  mutex_lock_nested+0x16/0x20 kernel/locking/mutex.c:908
>>  rtnl_lock+0x17/0x20 net/core/rtnetlink.c:74
>>  tc_action_net_exit include/net/act_api.h:125 [inline]
>>  bpf_exit_net+0x1a2/0x340 net/sched/act_bpf.c:408
>>  ops_exit_list.isra.6+0xae/0x150 net/core/net_namespace.c:142
>>  cleanup_net+0x5c7/0xb60 net/core/net_namespace.c:484
>>  process_one_work+0xbfd/0x1bc0 kernel/workqueue.c:2113
>>  worker_thread+0x223/0x1990 kernel/workqueue.c:2247
>>  kthread+0x37a/0x440 kernel/kthread.c:238
>>  ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:517
>>
[...]
>> Call Trace:
>>  serial_in drivers/tty/serial/8250/8250.h:111 [inline]
>>  wait_for_xmitr+0x93/0x1e0 drivers/tty/serial/8250/8250_port.c:2033

I saw this call trace on both 'bpf_exit_net task hung' and
'cleanup_net task hung'.
Note when cpu is here, it's still holding the rtnl_lock in these 2 cases,
one is in nl80211_dump_interface(), and the other one is in dev_ioctl().

I noticed this patch:

commit 54f19b4a679149130f78413c421a5780e90a9d0a
Author: Jiri Olsa <jolsa@...nel.org>
Date:   Wed Sep 21 16:43:15 2016 +0200

    tty/serial/8250: Touch NMI watchdog in wait_for_xmitr

It means in early time, watchdog timeout can be triggered here,
And this patch was to fix it by restarting NMI watchdog timeout
with calling touch_nmi_watchdog().

But this patch missed that it's still holding the rtnl_lock(), other
threads may timeout on watchdog when trying to acquire
rtnl_lock().


>>  serial8250_console_putchar+0x1f/0x60
>> drivers/tty/serial/8250/8250_port.c:3170
>>  uart_console_write+0xac/0xe0 drivers/tty/serial/serial_core.c:1858
>>  serial8250_console_write+0x647/0xa20
>> drivers/tty/serial/8250/8250_port.c:3236
>>  univ8250_console_write+0x5f/0x70 drivers/tty/serial/8250/8250_core.c:590
>>  call_console_drivers kernel/printk/printk.c:1574 [inline]
>>  console_unlock+0x788/0xd70 kernel/printk/printk.c:2233
>>  vprintk_emit+0x4ad/0x590 kernel/printk/printk.c:1757
>>  vprintk_default+0x28/0x30 kernel/printk/printk.c:1796
>>  vprintk_func+0x57/0xc0 kernel/printk/printk_safe.c:379
>>  printk+0xaa/0xca kernel/printk/printk.c:1829
>>  nla_parse+0x374/0x3d0 lib/nlattr.c:257
>>  nlmsg_parse include/net/netlink.h:398 [inline]
>>  nl80211_dump_wiphy_parse.isra.37.constprop.83+0x138/0x5c0
>> net/wireless/nl80211.c:1920
>>  nl80211_dump_interface+0x596/0x820 net/wireless/nl80211.c:2660
>>  genl_lock_dumpit+0x68/0x90 net/netlink/genetlink.c:480
>>  netlink_dump+0x48c/0xce0 net/netlink/af_netlink.c:2186
>>  __netlink_dump_start+0x4f0/0x6d0 net/netlink/af_netlink.c:2283
>>  genl_family_rcv_msg+0xd27/0xfc0 net/netlink/genetlink.c:548
>>  genl_rcv_msg+0xb2/0x140 net/netlink/genetlink.c:624
>>  netlink_rcv_skb+0x216/0x440 net/netlink/af_netlink.c:2405
>>  genl_rcv+0x28/0x40 net/netlink/genetlink.c:635
>>  netlink_unicast_kernel net/netlink/af_netlink.c:1272 [inline]
>>  netlink_unicast+0x4e8/0x6f0 net/netlink/af_netlink.c:1298
>>  netlink_sendmsg+0xa4a/0xe70 net/netlink/af_netlink.c:1861
>>  sock_sendmsg_nosec net/socket.c:636 [inline]
>>  sock_sendmsg+0xca/0x110 net/socket.c:646
>>  sock_write_iter+0x320/0x5e0 net/socket.c:915
>>  call_write_iter include/linux/fs.h:1776 [inline]
>>  new_sync_write fs/read_write.c:469 [inline]
>>  __vfs_write+0x68a/0x970 fs/read_write.c:482
>>  vfs_write+0x18f/0x510 fs/read_write.c:544
>>  SYSC_write fs/read_write.c:589 [inline]
>>  SyS_write+0xef/0x220 fs/read_write.c:581
>>  entry_SYSCALL_64_fastpath+0x1f/0x96
>> RIP: 0033:0x4529d9
>> RSP: 002b:00007f6d52e3ec58 EFLAGS: 00000212 ORIG_RAX: 0000000000000001
>> RAX: ffffffffffffffda RBX: 00007f6d52e3f700 RCX: 00000000004529d9
>> RDX: 0000000000000024 RSI: 0000000020454000 RDI: 0000000000000016
>> RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
>> R10: 0000000000000000 R11: 0000000000000212 R12: 0000000000000000
>> R13: 0000000000a6f7ff R14: 00007f6d52e3f9c0 R15: 0000000000000000
>> Code: 24 d9 00 00 00 49 8d 7c 24 40 48 b8 00 00 00 00 00 fc ff df 48 89 fa
>> 48 c1 ea 03 d3 e3 80 3c 02 00 75 17 41 03 5c 24 40 89 da ec <5b> 0f b6 c0 41
>> 5c 5d c3 e8 38 b0 18 ff eb c2 e8 91 b0 18 ff eb
>>
>>
>> ---
>> This bug is generated by a dumb bot. It may contain errors.
>> See https://goo.gl/tpsmEJ for details.
>> Direct all questions to syzkaller@...glegroups.com.
>> Please credit me with: Reported-by: syzbot <syzkaller@...glegroups.com>
>>
>> syzbot will keep track of this bug report.
>> Once a fix for this bug is merged into any tree, reply to this email with:
>> #syz fix: exact-commit-title
>> To mark this as a duplicate of another syzbot report, please reply with:
>> #syz dup: exact-subject-of-another-report
>> If it's a one-off invalid bug report, please reply with:
>> #syz invalid
>> Note: if the crash happens again, it will cause creation of a new bug
>> report.
>> Note: all commands must start from beginning of the line in the email body.
>>
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>
>
> This looks like +rtnetlink issue.

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