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authorSteven Rostedt (Red Hat) <rostedt@goodmis.org>2014-04-24 10:40:12 -0400
committerSteven Rostedt <rostedt@goodmis.org>2014-04-28 10:37:21 -0400
commita949ae560a511fe4e3adf48fa44fefded93e5c2b (patch)
treec47563e7c5696f264050aa5e049ad6f69787f536 /kernel
parenta798c10faf62a505d24e5f6213fbaf904a39623f (diff)
downloadlinux-a949ae560a511fe4e3adf48fa44fefded93e5c2b.tar.gz
linux-a949ae560a511fe4e3adf48fa44fefded93e5c2b.tar.xz
ftrace/module: Hardcode ftrace_module_init() call into load_module()
A race exists between module loading and enabling of function tracer. CPU 1 CPU 2 ----- ----- load_module() module->state = MODULE_STATE_COMING register_ftrace_function() mutex_lock(&ftrace_lock); ftrace_startup() update_ftrace_function(); ftrace_arch_code_modify_prepare() set_all_module_text_rw(); <enables-ftrace> ftrace_arch_code_modify_post_process() set_all_module_text_ro(); [ here all module text is set to RO, including the module that is loading!! ] blocking_notifier_call_chain(MODULE_STATE_COMING); ftrace_init_module() [ tries to modify code, but it's RO, and fails! ftrace_bug() is called] When this race happens, ftrace_bug() will produces a nasty warning and all of the function tracing features will be disabled until reboot. The simple solution is to treate module load the same way the core kernel is treated at boot. To hardcode the ftrace function modification of converting calls to mcount into nops. This is done in init/main.c there's no reason it could not be done in load_module(). This gives a better control of the changes and doesn't tie the state of the module to its notifiers as much. Ftrace is special, it needs to be treated as such. The reason this would work, is that the ftrace_module_init() would be called while the module is in MODULE_STATE_UNFORMED, which is ignored by the set_all_module_text_ro() call. Link: http://lkml.kernel.org/r/1395637826-3312-1-git-send-email-indou.takao@jp.fujitsu.com Reported-by: Takao Indoh <indou.takao@jp.fujitsu.com> Acked-by: Rusty Russell <rusty@rustcorp.com.au> Cc: stable@vger.kernel.org # 2.6.38+ Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Diffstat (limited to 'kernel')
-rw-r--r--kernel/module.c3
-rw-r--r--kernel/trace/ftrace.c27
2 files changed, 7 insertions, 23 deletions
diff --git a/kernel/module.c b/kernel/module.c
index 1186940..5f14fec 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -3271,6 +3271,9 @@ 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);
+
/* Finally it's fully formed, ready to start executing. */
err = complete_formation(mod, info);
if (err)
diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 1fd4b94..4a54a25 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -4330,16 +4330,11 @@ static void ftrace_init_module(struct module *mod,
ftrace_process_locs(mod, start, end);
}
-static int ftrace_module_notify_enter(struct notifier_block *self,
- unsigned long val, void *data)
+void ftrace_module_init(struct module *mod)
{
- struct module *mod = data;
-
- if (val == MODULE_STATE_COMING)
- ftrace_init_module(mod, mod->ftrace_callsites,
- mod->ftrace_callsites +
- mod->num_ftrace_callsites);
- return 0;
+ ftrace_init_module(mod, mod->ftrace_callsites,
+ mod->ftrace_callsites +
+ mod->num_ftrace_callsites);
}
static int ftrace_module_notify_exit(struct notifier_block *self,
@@ -4353,11 +4348,6 @@ static int ftrace_module_notify_exit(struct notifier_block *self,
return 0;
}
#else
-static int ftrace_module_notify_enter(struct notifier_block *self,
- unsigned long val, void *data)
-{
- return 0;
-}
static int ftrace_module_notify_exit(struct notifier_block *self,
unsigned long val, void *data)
{
@@ -4365,11 +4355,6 @@ static int ftrace_module_notify_exit(struct notifier_block *self,
}
#endif /* CONFIG_MODULES */
-struct notifier_block ftrace_module_enter_nb = {
- .notifier_call = ftrace_module_notify_enter,
- .priority = INT_MAX, /* Run before anything that can use kprobes */
-};
-
struct notifier_block ftrace_module_exit_nb = {
.notifier_call = ftrace_module_notify_exit,
.priority = INT_MIN, /* Run after anything that can remove kprobes */
@@ -4403,10 +4388,6 @@ void __init ftrace_init(void)
__start_mcount_loc,
__stop_mcount_loc);
- ret = register_module_notifier(&ftrace_module_enter_nb);
- if (ret)
- pr_warning("Failed to register trace ftrace module enter notifier\n");
-
ret = register_module_notifier(&ftrace_module_exit_nb);
if (ret)
pr_warning("Failed to register trace ftrace module exit notifier\n");