Re: Fw: [Bug 199109] New: pptp: kernel printk "recursion detected", and then reboot itself

On Wed, Mar 14, 2018 at 08:02:17AM -0700, Stephen Hemminger wrote:

Begin forwarded message:

Date: Wed, 14 Mar 2018 06:56:09 +0000
From: bugzilla-daemon@bugzilla.kernel.org
To: stephen@networkplumber.org
Subject: [Bug 199109] New: pptp: kernel printk "recursion detected", and then reboot itself


https://bugzilla.kernel.org/show_bug.cgi?id=199109

            Bug ID: 199109
           Summary: pptp: kernel printk "recursion detected", and then
                    reboot itself
           Product: Networking
           Version: 2.5
    Kernel Version: 4.9.77
          Hardware: Mips32
                OS: Linux
              Tree: Mainline
            Status: NEW
          Severity: high
          Priority: P1
         Component: IPV4
          Assignee: stephen@networkplumber.org
          Reporter: xuheng333@zoho.com
        Regression: No

Created attachment 274715
  --> https://bugzilla.kernel.org/attachment.cgi?id=274715&action=edit  
system log

Use openwrt LEDE, (gcc version 5.5.0 (OpenWrt GCC 5.5.0 r5932-9c4fe10) ).
When use pptp, make WAN(eth1) down and then make WAN(eth1) up, pptp will redial
itself. Do this in a loop.

After a while, kernel print "recursion detected" and "net_ratelimit: 49422
callbacks suppressed", print this many times, then system reboot.

When add more printk in driver "driver/net/ppp/ppp_generic.c", fond it fall in
loop in "static void __ppp_xmit_process(struct ppp *ppp)", which called by
"static void __ppp_channel_push(struct channel *pch)". 
__ppp_channel_push() locked ppp->xmit_recursion, and loop for long time( while
(!ppp->xmit_pending && (skb = skb_dequeue(&ppp->file.xq))) ppp_send_frame(ppp,
skb); ). Some other thread want to lock ppp->xmit_recursion, but failed.

Hi Xuheng,

Are you sure that your PPTP packets aren't routed back to your PPP
interface? What's the IP address of the PPTP server?

Regards,

Guillaume