linux-kernel - Re: [PATCH v8 7/9] livepatch: Improve the search performance of module_kallsyms_on_each

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Message-ID: <Y3IY6gzDtk1ze3u7@krava>
Date:   Mon, 14 Nov 2022 11:31:06 +0100
From:   Jiri Olsa <olsajiri@...il.com>
To:     "Leizhen (ThunderTown)" <thunder.leizhen@...wei.com>
Cc:     Jiri Olsa <olsajiri@...il.com>,
        Josh Poimboeuf <jpoimboe@...nel.org>,
        Jiri Kosina <jikos@...nel.org>,
        Miroslav Benes <mbenes@...e.cz>,
        Petr Mladek <pmladek@...e.com>,
        Joe Lawrence <joe.lawrence@...hat.com>,
        live-patching@...r.kernel.org, linux-kernel@...r.kernel.org,
        Masahiro Yamada <masahiroy@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Luis Chamberlain <mcgrof@...nel.org>,
        linux-modules@...r.kernel.org,
        Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...hat.com>,
        David Laight <David.Laight@...lab.com>,
        Stephen Rothwell <sfr@...b.auug.org.au>
Subject: Re: [PATCH v8 7/9] livepatch: Improve the search performance of
 module_kallsyms_on_each_symbol()

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

jirka