linux-kernel - Re: [PATCH 0/4] [GIT PULL] tracing: recursion and compile fixes

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Date:	Mon, 20 Apr 2009 15:55:55 -0400 (EDT)
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Ingo Molnar <mingo@...e.hu>
cc:	Frédéric Weisbecker <fweisbec@...il.com>,
	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 0/4] [GIT PULL] tracing: recursion and compile fixes


On Mon, 20 Apr 2009, Steven Rostedt wrote:

> 
> On Mon, 20 Apr 2009, Ingo Molnar wrote:
> > Running tests on all trace events:
> > Testing all events: <4>Tracing recursion: HC[0]:SC[0]:NMI[0]
> 
> Recursion is wrong :-/
> 
> > ------------[ cut here ]------------
> > WARNING: at kernel/trace/ring_buffer.c:1510 ring_buffer_lock_reserve+0xf7/0x1ce()
> > Hardware name: To Be Filled By O.E.M.
> > Pid: 1, comm: swapper Not tainted 2.6.30-rc2-tip-01538-ge8201b9-dirty #37740
> > Call Trace:
> >  <IRQ>  [<ffffffff80268a01>] warn_slowpath+0xcc/0x114
> >  [<ffffffff80299ed3>] ? trace_hardirqs_on_caller+0x11d/0x179
> >  [<ffffffff80299ba6>] ? mark_held_locks+0x60/0x95
> >  [<ffffffff802ca335>] ring_buffer_lock_reserve+0xf7/0x1ce
> >  [<ffffffff802ceb60>] trace_buffer_lock_reserve+0x34/0x7e
> >  [<ffffffff810c8f97>] ? do_IRQ+0xf/0xe8
> >  [<ffffffff802cf949>] trace_current_buffer_lock_reserve+0x36/0x4c
> >  [<ffffffff802d9da4>] function_test_events_call+0x7e/0xe2
> >  [<ffffffff80216313>] ? ret_from_intr+0x0/0x16
> >  [<ffffffff80215616>] ftrace_call+0x5/0x2b
> >  [<ffffffff8021630e>] ? common_interrupt+0xe/0x13
> >  [<ffffffff810c8f9c>] ? do_IRQ+0x14/0xe8
> 
> The function tracer was called before we updated the hardirq_count :-/
> 
> I liked the fact that we can detect same level recursion. Perhaps I'll 
> just make a depth test instead. Have a max of 16? times we can recurse 
> (should be plenty) and then bug if we hit it?
> 

The other option is not to trace any interrupt function that is called 
before "irq_enter". That would mean we would need to add notrace to do_IRQ 
and friends.

-- Steve

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