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

From: "Leizhen (ThunderTown)" <thunder.leizhen@huawei.com>
To: Jiri Olsa <olsajiri@gmail.com>
Cc: Josh Poimboeuf <jpoimboe@kernel.org>,
	Jiri Kosina <jikos@kernel.org>, Miroslav Benes <mbenes@suse.cz>,
	Petr Mladek <pmladek@suse.com>,
	Joe Lawrence <joe.lawrence@redhat.com>,
	<live-patching@vger.kernel.org>, <linux-kernel@vger.kernel.org>,
	Masahiro Yamada <masahiroy@kernel.org>,
	Alexei Starovoitov <ast@kernel.org>,
	Kees Cook <keescook@chromium.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	Luis Chamberlain <mcgrof@kernel.org>,
	<linux-modules@vger.kernel.org>,
	Steven Rostedt <rostedt@goodmis.org>,
	Ingo Molnar <mingo@redhat.com>,
	David Laight <David.Laight@aculab.com>,
	Stephen Rothwell <sfr@canb.auug.org.au>
Subject: Re: [PATCH v8 7/9] livepatch: Improve the search performance of module_kallsyms_on_each_symbol()
Date: Mon, 14 Nov 2022 19:30:16 +0800	[thread overview]
Message-ID: <955eebae-0b36-d13f-0199-2f1b32af7da6@huawei.com> (raw)
In-Reply-To: <Y3IY6gzDtk1ze3u7@krava>

On 2022/11/14 18:31, Jiri Olsa wrote:
> On Mon, Nov 14, 2022 at 06:00:38PM +0800, Leizhen (ThunderTown) wrote:
>>
>>
>> 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.
> 
> we take the module ref so it won't unload even outside of the
> module_kallsyms_on_each_symbol function

There's another way to do it, but it's more time consuming.

struct module *__module_text_address(unsigned long addr);
struct module *__module_address(unsigned long addr);

Which way do you think is more appropriate?

> 
> jirka
> .
> 

-- 
Regards,
  Zhen Lei