diff options
| author | Steven Rostedt (Red Hat) <rostedt@goodmis.org> | 2014-04-24 10:40:12 -0400 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2014-06-07 16:02:00 -0700 |
| commit | 8f4c0e8b5438725d66c6c27f11cb2a1c61c6d6c5 (patch) | |
| tree | d417790dc59d960c950e83511df582551c029b91 /kernel/module.c | |
| parent | 6427aede5eaac2e39a1d2b3306d960a603d7c3d9 (diff) | |
ftrace/module: Hardcode ftrace_module_init() call into load_module()
commit a949ae560a511fe4e3adf48fa44fefded93e5c2b upstream.
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>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'kernel/module.c')
| -rw-r--r-- | kernel/module.c | 3 |
1 files changed, 3 insertions, 0 deletions
diff --git a/kernel/module.c b/kernel/module.c index 85972171ecd3..5e398961b7b5 100644 --- a/kernel/module.c +++ b/kernel/module.c @@ -2951,6 +2951,9 @@ static struct module *load_module(void __user *umod, /* This has to be done once we're sure module name is unique. */ dynamic_debug_setup(info.debug, info.num_debug); + /* Ftrace init must be called in the MODULE_STATE_UNFORMED state */ + ftrace_module_init(mod); + /* Find duplicate symbols */ err = verify_export_symbols(mod); if (err < 0) |