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[for-next][PATCH 12/13] metag: ftrace: Fix the comments for ftrace_modify_code

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From: Li Bin <huawei.libin@huawei.com>

There is no need to worry about module and __init text disappearing
case, because that ftrace has a module notifier that is called when
a module is being unloaded and before the text goes away and this
code grabs the ftrace_lock mutex and removes the module functions
from the ftrace list, such that it will no longer do any
modifications to that module's text, the update to make functions
be traced or not is done under the ftrace_lock mutex as well.
And by now, __init section codes should not been modified
by ftrace, because it is black listed in recordmcount.c and
ignored by ftrace.

Link: http://lkml.kernel.org/r/1449367378-29430-3-git-send-email-huawei.libin@huawei.com

Cc: linux-metag@vger.kernel.org
Acked-by: James Hogan <james.hogan@imgtec.com>
Suggested-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Li Bin <huawei.libin@huawei.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
---
 arch/metag/kernel/ftrace.c | 11 +++++------
 1 file changed, 5 insertions(+), 6 deletions(-)

diff --git a/arch/metag/kernel/ftrace.c b/arch/metag/kernel/ftrace.c
index ed1d685157c2..ac8c039b0318 100644
--- a/arch/metag/kernel/ftrace.c
+++ b/arch/metag/kernel/ftrace.c
@@ -54,12 +54,11 @@ static int ftrace_modify_code(unsigned long pc, unsigned char *old_code,
 	unsigned char replaced[MCOUNT_INSN_SIZE];
 
 	/*
-	 * Note: Due to modules and __init, code can
-	 *  disappear and change, we need to protect against faulting
-	 *  as well as code changing.
-	 *
-	 * No real locking needed, this code is run through
-	 * kstop_machine.
+	 * Note:
+	 * We are paranoid about modifying text, as if a bug was to happen, it
+	 * could cause us to read or write to someplace that could cause harm.
+	 * Carefully read and modify the code with probe_kernel_*(), and make
+	 * sure what we read is what we expected it to be before modifying it.
 	 */
 
 	/* read the text we want to modify */
-- 
2.6.2


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[for-next][PATCH 00/13] tracing: More updates for 4.5. Steven Rostedt <rostedt@goodmis.org> - 2015-12-24 15:40 +0100
  [for-next][PATCH 06/13] tracing: Use seq_buf_used() in seq_buf_to_user() instead of len Steven Rostedt <rostedt@goodmis.org> - 2015-12-24 15:40 +0100
  [for-next][PATCH 01/13] ftrace: Fix a typo in comment Steven Rostedt <rostedt@goodmis.org> - 2015-12-24 15:40 +0100
  [for-next][PATCH 12/13] metag: ftrace: Fix the comments for ftrace_modify_code Steven Rostedt <rostedt@goodmis.org> - 2015-12-24 15:40 +0100
  [for-next][PATCH 03/13] ftrace: Remove use of control list and ops Steven Rostedt <rostedt@goodmis.org> - 2015-12-24 15:40 +0100
  [for-next][PATCH 07/13] tracing: Introduce TRACE_EVENT_FN_COND macro Steven Rostedt <rostedt@goodmis.org> - 2015-12-24 15:40 +0100
  [for-next][PATCH 04/13] ftrace: Have ftrace_ops_get_func() handle RCU and PER_CPU flags too Steven Rostedt <rostedt@goodmis.org> - 2015-12-24 15:40 +0100
  [for-next][PATCH 13/13] tracing: Fix comment to use tracing_on over tracing_enable Steven Rostedt <rostedt@goodmis.org> - 2015-12-24 15:40 +0100
  [for-next][PATCH 09/13] ftrace: Clean up ftrace_module_init() code Steven Rostedt <rostedt@goodmis.org> - 2015-12-24 15:40 +0100
  [for-next][PATCH 10/13] ia64: ftrace: Fix the comments for ftrace_modify_code() Steven Rostedt <rostedt@goodmis.org> - 2015-12-24 15:40 +0100
  [for-next][PATCH 02/13] ftrace: Fix output of enabled_functions for showing tramp Steven Rostedt <rostedt@goodmis.org> - 2015-12-24 15:40 +0100

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