From 17c367bc5caa07e8ce942349f8c2ce0f541ca266 Mon Sep 17 00:00:00 2001
From: Steven Rostedt <srostedt@redhat.com>
Date: Wed, 30 May 2012 13:36:38 -0400
Subject: [PATCH] --- yaml --- r: 310395 b: refs/heads/master c:
 8a4d0a687a599f39b7df3fe15f2d51d2157caf44 h: refs/heads/master i:   310393:
 1c2d13e7ff71aab86ad45d75cff9395f00c47bf6   310391:
 b16584e7b0121a20b1c3b7882cba5b4589e4a0c6 v: v3

---
 [refs]                         |  2 +-
 trunk/arch/x86/kernel/ftrace.c | 88 +++++++++++++++++++++++++++-------
 2 files changed, 73 insertions(+), 17 deletions(-)

diff --git a/[refs] b/[refs]
index ada6250c85fd..2356e5aa5a11 100644
--- a/[refs]
+++ b/[refs]
@@ -1,2 +1,2 @@
 ---
-refs/heads/master: a192cd0413b71c2a3e4e48dd365af704be72b748
+refs/heads/master: 8a4d0a687a599f39b7df3fe15f2d51d2157caf44
diff --git a/trunk/arch/x86/kernel/ftrace.c b/trunk/arch/x86/kernel/ftrace.c
index 2407a6d81cb7..c3a7cb4bf6e6 100644
--- a/trunk/arch/x86/kernel/ftrace.c
+++ b/trunk/arch/x86/kernel/ftrace.c
@@ -100,7 +100,7 @@ static const unsigned char *ftrace_nop_replace(void)
 }
 
 static int
-ftrace_modify_code(unsigned long ip, unsigned const char *old_code,
+ftrace_modify_code_direct(unsigned long ip, unsigned const char *old_code,
 		   unsigned const char *new_code)
 {
 	unsigned char replaced[MCOUNT_INSN_SIZE];
@@ -141,7 +141,20 @@ int ftrace_make_nop(struct module *mod,
 	old = ftrace_call_replace(ip, addr);
 	new = ftrace_nop_replace();
 
-	return ftrace_modify_code(rec->ip, old, new);
+	/*
+	 * On boot up, and when modules are loaded, the MCOUNT_ADDR
+	 * is converted to a nop, and will never become MCOUNT_ADDR
+	 * again. This code is either running before SMP (on boot up)
+	 * or before the code will ever be executed (module load).
+	 * We do not want to use the breakpoint version in this case,
+	 * just modify the code directly.
+	 */
+	if (addr == MCOUNT_ADDR)
+		return ftrace_modify_code_direct(rec->ip, old, new);
+
+	/* Normal cases use add_brk_on_nop */
+	WARN_ONCE(1, "invalid use of ftrace_make_nop");
+	return -EINVAL;
 }
 
 int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
@@ -152,20 +165,8 @@ int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
 	old = ftrace_nop_replace();
 	new = ftrace_call_replace(ip, addr);
 
-	return ftrace_modify_code(rec->ip, old, new);
-}
-
-int ftrace_update_ftrace_func(ftrace_func_t func)
-{
-	unsigned long ip = (unsigned long)(&ftrace_call);
-	unsigned char old[MCOUNT_INSN_SIZE], *new;
-	int ret;
-
-	memcpy(old, &ftrace_call, MCOUNT_INSN_SIZE);
-	new = ftrace_call_replace(ip, (unsigned long)func);
-	ret = ftrace_modify_code(ip, old, new);
-
-	return ret;
+	/* Should only be called when module is loaded */
+	return ftrace_modify_code_direct(rec->ip, old, new);
 }
 
 /*
@@ -201,6 +202,29 @@ int ftrace_update_ftrace_func(ftrace_func_t func)
  */
 atomic_t modifying_ftrace_code __read_mostly;
 
+static int
+ftrace_modify_code(unsigned long ip, unsigned const char *old_code,
+		   unsigned const char *new_code);
+
+int ftrace_update_ftrace_func(ftrace_func_t func)
+{
+	unsigned long ip = (unsigned long)(&ftrace_call);
+	unsigned char old[MCOUNT_INSN_SIZE], *new;
+	int ret;
+
+	memcpy(old, &ftrace_call, MCOUNT_INSN_SIZE);
+	new = ftrace_call_replace(ip, (unsigned long)func);
+
+	/* See comment above by declaration of modifying_ftrace_code */
+	atomic_inc(&modifying_ftrace_code);
+
+	ret = ftrace_modify_code(ip, old, new);
+
+	atomic_dec(&modifying_ftrace_code);
+
+	return ret;
+}
+
 /*
  * A breakpoint was added to the code address we are about to
  * modify, and this is the handle that will just skip over it.
@@ -520,6 +544,38 @@ void ftrace_replace_code(int enable)
 	}
 }
 
+static int
+ftrace_modify_code(unsigned long ip, unsigned const char *old_code,
+		   unsigned const char *new_code)
+{
+	int ret;
+
+	ret = add_break(ip, old_code);
+	if (ret)
+		goto out;
+
+	run_sync();
+
+	ret = add_update_code(ip, new_code);
+	if (ret)
+		goto fail_update;
+
+	run_sync();
+
+	ret = ftrace_write(ip, new_code, 1);
+	if (ret) {
+		ret = -EPERM;
+		goto out;
+	}
+	run_sync();
+ out:
+	return ret;
+
+ fail_update:
+	probe_kernel_write((void *)ip, &old_code[0], 1);
+	goto out;
+}
+
 void arch_ftrace_update_code(int command)
 {
 	/* See comment above by declaration of modifying_ftrace_code */