History

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

Steven Rostedt (Red Hat) committed 12 years ago

Commit a949ae51 parent a798c103 files · +9 −23Browse files

Unified · Split

3 files
  1. include/linux/ftrace.h +2 −0
  2. kernel/module.c +3 −0
  3. kernel/trace/ftrace.c +4 −23
include/linux/ftrace.h+2−0
@@ -535,6 +535,7 @@ static inline int ftrace_modify_call(struct dyn_ftrace *rec, unsigned long old_a · 534 unmodified lines
535extern int ftrace_arch_read_dyn_info(char *buf, int size);535extern int ftrace_arch_read_dyn_info(char *buf, int size);
536 536
537extern int skip_trace(unsigned long ip);537extern int skip_trace(unsigned long ip);
538extern void ftrace_module_init(struct module *mod);
538 539
539extern void ftrace_disable_daemon(void);540extern void ftrace_disable_daemon(void);
540extern void ftrace_enable_daemon(void);541extern void ftrace_enable_daemon(void);
@@ -544,6 +545,7 @@ static inline int ftrace_force_update(void) { return 0; } · 3 unmodified lines
544static inline void ftrace_disable_daemon(void) { }545static inline void ftrace_disable_daemon(void) { }
545static inline void ftrace_enable_daemon(void) { }546static inline void ftrace_enable_daemon(void) { }
546static inline void ftrace_release_mod(struct module *mod) {}547static inline void ftrace_release_mod(struct module *mod) {}
548static inline void ftrace_module_init(struct module *mod) {}
547static inline __init int register_ftrace_command(struct ftrace_func_command *cmd)549static inline __init int register_ftrace_command(struct ftrace_func_command *cmd)
548{550{
549 return -EINVAL;551 return -EINVAL;
kernel/module.c+3−0
@@ -3271,6 +3271,9 @@ static int load_module(struct load_info *info, const char __user *uargs, · 3270 unmodified lines
3271 3271
3272 dynamic_debug_setup(info->debug, info->num_debug);3272 dynamic_debug_setup(info->debug, info->num_debug);
3273 3273
3274 /* Ftrace init must be called in the MODULE_STATE_UNFORMED state */
3275 ftrace_module_init(mod);
3276
3274 /* Finally it's fully formed, ready to start executing. */3277 /* Finally it's fully formed, ready to start executing. */
3275 err = complete_formation(mod, info);3278 err = complete_formation(mod, info);
3276 if (err)3279 if (err)
kernel/trace/ftrace.c+4−23
@@ -4330,16 +4330,11 @@ static void ftrace_init_module(struct module *mod, · 4329 unmodified lines
4330 ftrace_process_locs(mod, start, end);4330 ftrace_process_locs(mod, start, end);
4331}4331}
4332 4332
4333static int ftrace_module_notify_enter(struct notifier_block *self,4333void ftrace_module_init(struct module *mod)
4334 unsigned long val, void *data)
4335{4334{
4336 struct module *mod = data;4335 ftrace_init_module(mod, mod->ftrace_callsites,
4337 4336 mod->ftrace_callsites +
4338 if (val == MODULE_STATE_COMING)4337 mod->num_ftrace_callsites);
4339 ftrace_init_module(mod, mod->ftrace_callsites,
4340 mod->ftrace_callsites +
4341 mod->num_ftrace_callsites);
4342 return 0;
4343}4338}
4344 4339
4345static int ftrace_module_notify_exit(struct notifier_block *self,4340static int ftrace_module_notify_exit(struct notifier_block *self,
@@ -4353,11 +4348,6 @@ static int ftrace_module_notify_exit(struct notifier_block *self, · 7 unmodified lines
4353 return 0;4348 return 0;
4354}4349}
4355#else4350#else
4356static int ftrace_module_notify_enter(struct notifier_block *self,
4357 unsigned long val, void *data)
4358{
4359 return 0;
4360}
4361static int ftrace_module_notify_exit(struct notifier_block *self,4351static int ftrace_module_notify_exit(struct notifier_block *self,
4362 unsigned long val, void *data)4352 unsigned long val, void *data)
4363{4353{
@@ -4365,11 +4355,6 @@ static int ftrace_module_notify_exit(struct notifier_block *self, · 1 unmodified line
4365}4355}
4366#endif /* CONFIG_MODULES */4356#endif /* CONFIG_MODULES */
4367 4357
4368struct notifier_block ftrace_module_enter_nb = {
4369 .notifier_call = ftrace_module_notify_enter,
4370 .priority = INT_MAX, /* Run before anything that can use kprobes */
4371};
4372
4373struct notifier_block ftrace_module_exit_nb = {4358struct notifier_block ftrace_module_exit_nb = {
4374 .notifier_call = ftrace_module_notify_exit,4359 .notifier_call = ftrace_module_notify_exit,
4375 .priority = INT_MIN, /* Run after anything that can remove kprobes */4360 .priority = INT_MIN, /* Run after anything that can remove kprobes */
@@ -4403,10 +4388,6 @@ void __init ftrace_init(void) · 27 unmodified lines
4403 __start_mcount_loc,4388 __start_mcount_loc,
4404 __stop_mcount_loc);4389 __stop_mcount_loc);
4405 4390
4406 ret = register_module_notifier(&ftrace_module_enter_nb);
4407 if (ret)
4408 pr_warning("Failed to register trace ftrace module enter notifier\n");
4409
4410 ret = register_module_notifier(&ftrace_module_exit_nb);4391 ret = register_module_notifier(&ftrace_module_exit_nb);
4411 if (ret)4392 if (ret)
4412 pr_warning("Failed to register trace ftrace module exit notifier\n");4393 pr_warning("Failed to register trace ftrace module exit notifier\n");