[PATCH] ftrace: fix race between ftrace and insmod

["Qiu, PeiyangX" <peiyangx.qiu@intel.com>]

We hit ftrace_bug report when booting Android on a 64bit ATOM SOC chip.
Basically, there is a race between insmod and ftrace_run_update_code.

After load_module=>ftrace_module_init, another thread jumps in to call
ftrace_run_update_code=>ftrace_arch_code_modify_prepare
                         =>set_all_modules_text_rw, to change all modules
as RW. Since the new module is at MODULE_STATE_UNFORMED, the text attribute
is not changed. Then, the 2nd thread goes ahead to change codes.
However, load_module continues to call 
complete_formation=>set_section_ro_nx,
then 2nd thread would fail when probing the module's TEXT.

Below patch tries to resolve it.

commit a949ae560a511fe4e3adf48fa44fefded93e5c2b
Author: Steven Rostedt (Red Hat) <rostedt@goodmis.org>
Date:   Thu Apr 24 10:40:12 2014 -0400

     ftrace/module: Hardcode ftrace_module_init() call into load_module()

But it can't fully resolve the issue.

THis patch holds ftrace_mutex across ftrace_module_init and
complete_formation.

Signed-off-by: Qiu Peiyang <peiyangx.qiu@intel.com>
Signed-off-by: Zhang Yanmin <yanmin.zhang@intel.com>
---
  include/linux/ftrace.h |  6 ++++--
  kernel/module.c        |  3 ++-
  kernel/trace/ftrace.c  | 33 ++++++++++++++++++++++-----------
  3 files changed, 28 insertions(+), 14 deletions(-)

diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h
index eae6548..4adc279 100644
--- a/include/linux/ftrace.h
+++ b/include/linux/ftrace.h
@@ -585,7 +585,8 @@ static inline int ftrace_modify_call(struct 
dyn_ftrace *rec, unsigned long old_a
  extern int ftrace_arch_read_dyn_info(char *buf, int size);

  extern int skip_trace(unsigned long ip);
-extern void ftrace_module_init(struct module *mod);
+extern void ftrace_module_init_start(struct module *mod);
+extern void ftrace_module_init_end(struct module *mod);

  extern void ftrace_disable_daemon(void);
  extern void ftrace_enable_daemon(void);
@@ -595,7 +596,8 @@ static inline int ftrace_force_update(void) { return 
0; }
  static inline void ftrace_disable_daemon(void) { }
  static inline void ftrace_enable_daemon(void) { }
  static inline void ftrace_release_mod(struct module *mod) {}
-static inline void ftrace_module_init(struct module *mod) {}
+static inline void ftrace_module_init_start(struct module *mod) {}
+static inline void ftrace_module_init_end(struct module *mod) {}
  static inline __init int register_ftrace_command(struct 
ftrace_func_command *cmd)
  {
      return -EINVAL;
diff --git a/kernel/module.c b/kernel/module.c
index 8f051a1..324c5c6 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -3506,10 +3506,11 @@ static int load_module(struct load_info *info, 
const char __user *uargs,
      dynamic_debug_setup(info->debug, info->num_debug);

      /* Ftrace init must be called in the MODULE_STATE_UNFORMED state */
-    ftrace_module_init(mod);
+    ftrace_module_init_start(mod);

      /* Finally it's fully formed, ready to start executing. */
      err = complete_formation(mod, info);
+    ftrace_module_init_end(mod);
      if (err)
          goto ddebug_cleanup;

diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 3f743b1..436c199 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -4795,7 +4795,7 @@ static int ftrace_cmp_ips(const void *a, const 
void *b)
      return 0;
  }

-static int ftrace_process_locs(struct module *mod,
+static int ftrace_process_locs_nolock(struct module *mod,
                     unsigned long *start,
                     unsigned long *end)
  {
@@ -4820,8 +4820,6 @@ static int ftrace_process_locs(struct module *mod,
      if (!start_pg)
          return -ENOMEM;

-    mutex_lock(&ftrace_lock);
-
      /*
       * Core and each module needs their own pages, as
       * modules will free them when they are removed.
@@ -4889,8 +4887,18 @@ static int ftrace_process_locs(struct module *mod,
          local_irq_restore(flags);
      ret = 0;
   out:
-    mutex_unlock(&ftrace_lock);
+    return ret;
+}

+static int ftrace_process_locs(struct module *mod,
+                   unsigned long *start,
+                   unsigned long *end)
+{
+    int ret;
+
+    mutex_lock(&ftrace_lock);
+    ret = ftrace_process_locs_nolock(mod, start, end);
+    mutex_unlock(&ftrace_lock);
      return ret;
  }

@@ -4940,19 +4948,22 @@ void ftrace_release_mod(struct module *mod)
      mutex_unlock(&ftrace_lock);
  }

-static void ftrace_init_module(struct module *mod,
-                   unsigned long *start, unsigned long *end)
+void ftrace_module_init_start(struct module *mod)
  {
+    unsigned long *start = mod->ftrace_callsites;
+    unsigned long *end = mod->ftrace_callsites + mod->num_ftrace_callsites;
+
+    mutex_lock(&ftrace_lock);
+
      if (ftrace_disabled || start == end)
          return;
-    ftrace_process_locs(mod, start, end);
+
+    ftrace_process_locs_nolock(mod, start, end);
  }

-void ftrace_module_init(struct module *mod)
+void ftrace_module_init_end(struct module *mod)
  {
-    ftrace_init_module(mod, mod->ftrace_callsites,
-               mod->ftrace_callsites +
-               mod->num_ftrace_callsites);
+    mutex_unlock(&ftrace_lock);
  }

  static int ftrace_module_notify_exit(struct notifier_block *self,
-- 
1.9.1