linux-kernel - [PATCH] ftrace: initialize the ftrace profile for each possible cpu

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Date:	Mon, 16 Dec 2013 15:20:01 +0800
From:	Miao Xie <miaox@...fujitsu.com>
To:	rostedt@...dmis.org, fweisbec@...il.com, mingo@...hat.com
Cc:	linux-kernel@...r.kernel.org
Subject: [PATCH] ftrace: initialize the ftrace profile for each possible cpu

We just initialize the ftrace profile for each online cpu currently, this
implementation has two problems:
- If we online a CPU after we enable the function profile, and then run the
  test, we will lose the trace information on that CPU.
  Steps to reproduce:
  # echo 0 > /sys/devices/system/cpu/cpu1/online
  # cd <debugfs>/tracing/
  # echo <some function name> >> set_ftrace_filter
  # echo 1 > function_profile_enabled
  # echo 1 > /sys/devices/system/cpu/cpu1/online
  # run test
- If we offline a CPU before we enable the function profile, we will not clear
  the trace information when we enable the function profile. It will trouble
  the users.
  Steps to reproduce:
  # cd <debugfs>/tracing/
  # echo <some function name> >> set_ftrace_filter
  # echo 1 > function_profile_enabled
  # run test
  # cat trace_stat/function*
  # echo 0 > /sys/devices/system/cpu/cpu1/online
  # echo 0 > function_profile_enabled
  # echo 1 > function_profile_enabled
  # cat trace_stat/function*
  # run test
  # cat trace_stat/function*

So it is better that initialize the ftrace profile for each possible cpu
every time we enable the function profile, not only for each online cpu.

Signed-off-by: Miao Xie <miaox@...fujitsu.com>
---
 kernel/trace/ftrace.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 0e9f9ea..72a0f81 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -775,7 +775,7 @@ static int ftrace_profile_init(void)
 	int cpu;
 	int ret = 0;
 
-	for_each_online_cpu(cpu) {
+	for_each_possible_cpu(cpu) {
 		ret = ftrace_profile_init_cpu(cpu);
 		if (ret)
 			break;
-- 
1.8.3.1

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