Re: Re: [PATCH] module: Introduce MODULE_STATE_COMING_FINAL to avoid ftrace warning

[Masami Hiramatsu]

(2014/04/14 11:49), Takao Indoh wrote:
> ping, any comments?
> 
> (2014/04/02 16:54), Takao Indoh wrote:
>> This patch adds new module state MODULE_STATE_COMING_FINAL to avoid
>> ftrace waring message when loading two modules simultaneously.
>>
>> The original patch was written by Steven Rostedt, see below.
>> https://lkml.org/lkml/2014/3/24/242
>>
>> Ftrace waring message below is got when insmod two modules almost at the
>> same time and at least one of them uses register_kprobe() in its
>> module_init.
>>
>> [  409.337936] ------------[ cut here ]------------
>> [  409.337945] WARNING: CPU: 12 PID: 10028 at /mnt/repos/linux/kernel/trace/ftrace.c:1716 ftrace_bug+0x206/0x270()
>> (snip)
>> [  409.337983] Call Trace:
>> [  409.337990]  [<ffffffff81547bfe>] dump_stack+0x45/0x56
>> [  409.337993]  [<ffffffff81049a0d>] warn_slowpath_common+0x7d/0xa0
>> [  409.337997]  [<ffffffffa0364000>] ? 0xffffffffa0363fff
>> [  409.337999]  [<ffffffff81049aea>] warn_slowpath_null+0x1a/0x20
>> [  409.338001]  [<ffffffff810e79f6>] ftrace_bug+0x206/0x270
>> [  409.338004]  [<ffffffffa0364000>] ? 0xffffffffa0363fff
>> [  409.338006]  [<ffffffff810e7d8e>] ftrace_process_locs+0x32e/0x710
>> [  409.338008]  [<ffffffff810e8206>] ftrace_module_notify_enter+0x96/0xf0
>> [  409.338012]  [<ffffffff81551dec>] notifier_call_chain+0x4c/0x70
>> [  409.338018]  [<ffffffff8106fbfd>] __blocking_notifier_call_chain+0x4d/0x70
>> [  409.338020]  [<ffffffff8106fc36>] blocking_notifier_call_chain+0x16/0x20
>> [  409.338026]  [<ffffffff810bf3f4>] load_module+0x1f54/0x25d0
>> [  409.338028]  [<ffffffff810baab0>] ? store_uevent+0x40/0x40
>> [  409.338031]  [<ffffffff810bfbe6>] SyS_finit_module+0x86/0xb0
>> [  409.338036]  [<ffffffff81556752>] system_call_fastpath+0x16/0x1b
>> [  409.338037] ---[ end trace e7e27c36e7a65831 ]---
>> [  409.338040] ftrace faulted on writing [<ffffffffa0364000>] handler_pre+0x0/0x10 [test2]
>>
>> This is the sequence when this problem occurs.
>>
>> <insmod module A>
>> init_module
>>    load_module
>>      do_init_module
>>        do_one_initcall
>>          (module_init)
>>            register_kprobe
>>              arm_kprobe
>>                arm_kprobe_ftrace
>>                  register_ftrace_function
>>                    mutex_lock(&ftrace_lock) ------------------- (1)
>>                    ftrace_startup
>>                      ftrace_startup_enable
>>                        ftrace_run_update_code
>>                          ftrace_arch_code_modify_post_process
>>                            set_all_modules_text_ro ------------ (2)
>>                    mutex_unlock(&ftrace_lock) ----------------- (3)
>>
>> <insmod module B>
>> init_module
>>    load_module
>>      do_init_module
>>        blocking_notifier_call_chain
>>          ftrace_module_notify_enter
>>            ftrace_init_module
>>              ftrace_process_locs
>>               mutex_lock(&ftrace_lock) ------------------------ (4)
>>               ftrace_update_code
>>                 __ftrace_replace_code
>>                   ftrace_make_nop
>>                     ftrace_modify_code_direct
>>                       do_ftrace_mod_code
>>                         probe_kernel_write -------------------- (5)
>>
>> o Module A gets ftrace_lock at (1)
>> o Module B also tries to get ftrace_lock at (4) somewhat late, and waits
>>    here because module A got it.
>> o Module A sets all modules text to ReadOnly at (2), and then release
>>    ftrace_lock at (3)
>> o Module B wakes up and tries to rewrite its text at (5), but it fails
>>    because it is already changed to RO at (2) by modules A. The ftrace
>>    waring message is outputted.
>>
>> This patch introduces MODULE_STATE_COMING_FINAL which means that the
>> module is ready to be changed to ReadOnly. By this, the modules B is not
>> change to RO at (2) because its state is still MODULE_STATE_COMING, so
>> this warning message is avoided. Module B is changed to RO in the
>> do_init_module() after comes back from notifier.
>>
>> Signed-off-by: Takao Indoh <indou.takao@xxxxxxxxxxxxxx>

As Steven said, it should have his signed-off too, anyway,

Reviewed-by: Masami Hiramatsu <masami.hiramatsu.pt@xxxxxxxxxxx>

Thank you,

>> ---
>>   include/linux/module.h |  9 +++++----
>>   kernel/module.c        | 13 ++++++++++++-
>>   2 files changed, 17 insertions(+), 5 deletions(-)
>>
>> diff --git a/include/linux/module.h b/include/linux/module.h
>> index eaf60ff..32f4481 100644
>> --- a/include/linux/module.h
>> +++ b/include/linux/module.h
>> @@ -207,10 +207,11 @@ struct module_use {
>>   };
>>   
>>   enum module_state {
>> -	MODULE_STATE_LIVE,	/* Normal state. */
>> -	MODULE_STATE_COMING,	/* Full formed, running module_init. */
>> -	MODULE_STATE_GOING,	/* Going away. */
>> -	MODULE_STATE_UNFORMED,	/* Still setting it up. */
>> +	MODULE_STATE_LIVE,		/* Normal state. */
>> +	MODULE_STATE_COMING,		/* Full formed, running module_init. */
>> +	MODULE_STATE_COMING_FINAL,	/* Ready to be changed to read only. */
>> +	MODULE_STATE_GOING,		/* Going away. */
>> +	MODULE_STATE_UNFORMED,		/* Still setting it up. */
>>   };
>>   
>>   /**
>> diff --git a/kernel/module.c b/kernel/module.c
>> index 8dc7f5e..94b9f91 100644
>> --- a/kernel/module.c
>> +++ b/kernel/module.c
>> @@ -1033,6 +1033,9 @@ static ssize_t show_initstate(struct module_attribute *mattr,
>>   	case MODULE_STATE_COMING:
>>   		state = "coming";
>>   		break;
>> +	case MODULE_STATE_COMING_FINAL:
>> +		state = "coming_final";
>> +		break;
>>   	case MODULE_STATE_GOING:
>>   		state = "going";
>>   		break;
>> @@ -1805,7 +1808,8 @@ void set_all_modules_text_ro(void)
>>   
>>   	mutex_lock(&module_mutex);
>>   	list_for_each_entry_rcu(mod, &modules, list) {
>> -		if (mod->state == MODULE_STATE_UNFORMED)
>> +		if (mod->state == MODULE_STATE_UNFORMED ||
>> +		    mod->state == MODULE_STATE_COMING)
>>   			continue;
>>   		if ((mod->module_core) && (mod->core_text_size)) {
>>   			set_page_attributes(mod->module_core,
>> @@ -3024,6 +3028,13 @@ static int do_init_module(struct module *mod)
>>   	blocking_notifier_call_chain(&module_notify_list,
>>   			MODULE_STATE_COMING, mod);
>>   
>> +	/*
>> +	 * This module must not be changed by set_all_modules_text_ro()
>> +	 * until we get here. Otherwise notifiers that change text
>> +	 * (like ftrace does) will break.
>> +	 */
>> +	mod->state = MODULE_STATE_COMING_FINAL;
>> +
>>   	/* Set RO and NX regions for core */
>>   	set_section_ro_nx(mod->module_core,
>>   				mod->core_text_size,
>>
> 


-- 
Masami HIRAMATSU
Software Platform Research Dept. Linux Technology Center
Hitachi, Ltd., Yokohama Research Laboratory
E-mail: masami.hiramatsu.pt@xxxxxxxxxxx


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