linux-kernel - Re: [PATCH v2] tracing/function-graph-tracer: prevent from hrtimer interrupt infinite loop

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Date:	Sun, 21 Dec 2008 13:21:12 +0100
From:	"Frédéric Weisbecker" <fweisbec@...il.com>
To:	"Ingo Molnar" <mingo@...e.hu>
Cc:	"Thomas Gleixner" <tglx@...utronix.de>,
	"Steven Rostedt" <rostedt@...dmis.org>,
	"Andrew Morton" <akpm@...ux-foundation.org>,
	"Linux Kernel" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] tracing/function-graph-tracer: prevent from hrtimer interrupt infinite loop

2008/12/21 Ingo Molnar <mingo@...e.hu>:
>
> btw., a graph-tracer buglet i noticed:
>
>  3)               |  perf_counter_task_tick() {
>  3)               |    perf_counter_task_sched_out() {
>  3)               |      /* c:ffff88049b184000, u:0: 0000000020ca1ab0 + 0000000000000000 = 0000000020ca1ab0
>  */
>  3)               |      /* sched-out counter ffff88049b184000, state: 0
>  */
>  3)   5.024 us    |    }
>  3)               |    perf_counter_task_sched_in() {
>  3)               |      /* c:ffff88049b184000, u:0: 0000000020ca1ab0 + 0000000000000000 = 0000000020ca1ab0
>  */
>  3)               |      /* sched-in counter ffff88049b184000, state: 1
>  */
>  3)   2.605 us    |    }
>  3)   9.714 us    |  }
>  3)               |  perf_counter_task_tick() {
>
> the bug is that the '*/' comment closing text is printed in the next line
> - that's not a linewrap, it happened like this in the trace.
>
> The reason is that the ftrace_printk did:
>
>        ftrace_printk("c:%p, u:%d: %016Lx + %016Lx = %016Lx\n",
>
> the closing \n is pretty natural - especially for kernel hackers who might
> just turn printk()s into ftrace_printk(), to embedd printouts in function
> traces. So it would be nice if ftrace skipped over \n's when printing them
> out as embedded C comments.
>
>        Ingo
>


Yes I was afraid of the \n from the user for these comments. You're
right, I will skip the newlines
from the user.


2008/12/21 Ingo Molnar <mingo@...e.hu>:
>
> * Ingo Molnar <mingo@...e.hu> wrote:
>
>> btw., a graph-tracer buglet i noticed:
>
> another thing. I turned off all the options that come ahead of the 'meat'
> of the trace data:
>
> # cat /debug/tracing/trace_options
> print-parent nosym-offset nosym-addr noverbose noraw nohex nobin noblock
> nostacktrace nosched-tree ftrace_printk noftrace_preempt nobranch annotate
> nouserstacktrace nosym-userobj printk-msg-only nofuncgraph-overrun
> nofuncgraph-cpu nofuncgraph-overhead nofuncgraph-proc
>
> but i still got the 'duration' field printed:
>
> # tracer: function_graph
> #
> # DURATION            FUNCTION CALLS
> #     |               |   |   |   |
>
> 0.865 us    |    }
>            |    alloc_page_vma() {
> 0.295 us    |      get_vma_policy();
> 0.268 us    |      policy_zonelist();
>            |      __alloc_pages_internal() {
> 0.257 us    |        __might_sleep();
>            |        get_page_from_freelist() {
>
>
> i'd have expected to only see the flow of execution as it happens.
>
>        Ingo
>


Strange. I will test that.
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