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

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Date:	Sun, 21 Dec 2008 11:00:47 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Frédéric Weisbecker <fweisbec@...il.com>
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


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
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