linux-kernel - Re: Kernel crash with repeated NF invocation

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Date:	Thu, 10 Feb 2011 00:52:33 +0100 (CET)
From:	Jan Engelhardt <jengelh@...ozas.de>
To:	David Miller <davem@...emloft.net>
cc:	netfilter-devel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: Kernel crash with repeated NF invocation


On Thursday 2011-02-03 22:10, David Miller wrote:

>>I remember there being a kernel config option
>>(CONFIG_DEBUG_STACKOVERFLOW) that would emit messages similar to
>>"process foobar (12345) used greatest stack depth: 2042" -- would
>>that also work for softirqs?
>
>The kernel stack tracer is your best bet right now, it's easy to
>enable, it's something like just writing "1" to the /sys filesystem
>file that controls it.
>
>config STACK_TRACER
>	  This special tracer records the maximum stack footprint of the
>	  kernel and displays it in /sys/kernel/debug/tracing/stack_trace.
>
>	  This tracer works by hooking into every function call that the
>	  kernel executes, and keeping a maximum stack depth value and
>	  stack-trace saved.  If this is configured with DYNAMIC_FTRACE
>	  then it will not have any overhead while the stack tracer
>	  is disabled.

Compiled with DYNAMIC_FTRACE=y, and enabled (writing 1
to /sys/kernel/debug/tracing/tracing_enabled). In the stack_trace
file I can find some lines..

        Depth    Size   Location    (56 entries)
        -----    ----   --------
  0)     5496      48   stack_trace_call+0xfa/0x1aa
  1)     5448     112   ftrace_call+0x5/0x2b
  2)     5336      64   zone_watermark_ok+0x29/0xbf
  3)     5272     288   get_page_from_freelist+0x1b7/0x6ab
  4)     4984     240   __alloc_pages_nodemask+0x11b/0x70e
  5)     4744      48   kmem_getpages+0x65/0x10e
  6)     4696     128   cache_grow+0xc4/0x285
  7)     4568      96   ____cache_alloc+0x21e/0x26d
  8)     4472      64   kmem_cache_alloc+0x5e/0xfb
  9)     4408      16   mempool_alloc_slab+0x15/0x17
 10)     4392     144   mempool_alloc+0x52/0x104
 11)     4248      32   scsi_sg_alloc+0x2d/0x2f
etc.
 
Does the file cover all CPUs and past function executions, is there a
timeout on these entries? At other times, running cat on that file
merely yields 2 entries, being the stack tracing itself.
Will this list dumped to the console in case of a
bug/oops/Illegal_IP?


thanks,
Jan
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