Re: [PATCH v8 7/9] livepatch: Improve the search performance of module_kallsyms_on_each_symbol()

Leizhen (ThunderTown)
2022-11-14T10:04:43Z

On 2022/11/14 17:27, Jiri Olsa wrote:
> On Mon, Nov 14, 2022 at 04:50:25PM +0800, Leizhen (ThunderTown) wrote:
>>
>> On 2022/11/14 15:47, Jiri Olsa wrote:
>>> On Wed, Nov 02, 2022 at 04:49:19PM +0800, Zhen Lei wrote:
>>>> Currently we traverse all symbols of all modules to find the specified
>>>> function for the specified module. But in reality, we just need to find
>>>> the given module and then traverse all the symbols in it.
>>> hi,
>>> sorry for delayed answer, I did not notice this until Stephen's email
>>> about merge issue with recent bpf change [1]
>>>
>>>> Let's add a new parameter 'const char *modname' to function
>>>> module_kallsyms_on_each_symbol(), then we can compare the module names
>>> we have use case for iterating all modules and their symbols when we
>>> want to resolve passed addresses for tracing
>>>
>>> we don't have 'modname' that we could pass, we need to iterate all modules
>>>
>>> so perhaps this could be made optional like with passing NULL for modname?
>> The deletion of modname was suggested by Petr Mladek. The reason is that
>> everyone passes modname as NULL, there was no actual demand at the time.
>> https://lkml.org/lkml/2022/9/20/682
>>
>>>> directly in this function and call hook 'fn' after matching. And the
>>>> parameter 'struct module *' in the hook 'fn' can also be deleted.
>>> we need 'struct module *' argument in the callback as well because we are
>>> taking the module reference if we trace function in it, so it wont get
>>> unloaded
>>>
>>> please let me know if I should do the change or can help in any way
>> It seems that we should take the module reference before invoking callback
>> and put it after it is called, without passing modname.
> we take the module ref only if we (callback) find the traced address in
> the module, we don't have the module object before
>
> jirka
>

Do it in function module_kallsyms_on_each_symbol()?

But I just saw that mutex_lock(&module_mutex) protection is already
provided in this function. So reference counting protection may not
be required.

--
Regards,
Zhen Lei