netdev - Re: Repeatable inet6_dump_fib crash in stock 4.12.0-rc4+

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Message-ID: <20170620180515.GB6104@unicorn.suse.cz>
Date:   Tue, 20 Jun 2017 20:05:15 +0200
From:   Michal Kubecek <mkubecek@...e.cz>
To:     Ben Greear <greearb@...delatech.com>
Cc:     David Ahern <dsahern@...il.com>,
        Cong Wang <xiyou.wangcong@...il.com>,
        Eric Dumazet <eric.dumazet@...il.com>,
        netdev <netdev@...r.kernel.org>
Subject: Re: Repeatable inet6_dump_fib crash in stock 4.12.0-rc4+

On Tue, Jun 20, 2017 at 07:12:27AM -0700, Ben Greear wrote:
> On 06/14/2017 03:25 PM, David Ahern wrote:
> >On 6/14/17 4:23 PM, Ben Greear wrote:
> >>On 06/13/2017 07:27 PM, David Ahern wrote:
> >>
> >>>Let's try a targeted debug patch. See attached
> >>
> >>I had to change it to pr_err so it would go to our serial console
> >>since the system locked hard on crash,
> >>and that appears to be enough to change the timing where we can no longer
> >>reproduce the problem.
> >
> >
> >ok, let's figure out which one is doing that. There are 3 debug
> >statements. I suspect fib6_del_route is the one setting the state to
> >FWS_U. Can you remove the debug prints in fib6_repair_tree and
> >fib6_walk_continue and try again?
> 
> We cannot reproduce with just that one printf in the kernel either.  It
> must change the timing too much to trigger the bug.

You might try trace_printk() which should have less impact (don't forget
to enable /proc/sys/kernel/ftrace_dump_on_oops).

Michal Kubecek