linux-kernel - Re: [PATCH 5/8] module: Add module_for_each

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Message-Id: <20250206142817.91853f475c681bc2ef7ca962@kernel.org>
Date: Thu, 6 Feb 2025 14:28:17 +0900
From: Masami Hiramatsu (Google) <mhiramat@...nel.org>
To: Steven Rostedt <rostedt@...dmis.org>
Cc: linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org, Masami
 Hiramatsu <mhiramat@...nel.org>, Mark Rutland <mark.rutland@....com>,
 Mathieu Desnoyers <mathieu.desnoyers@...icios.com>, Andrew Morton
 <akpm@...ux-foundation.org>, Luis Chamberlain <mcgrof@...nel.org>, Petr
 Pavlu <petr.pavlu@...e.com>, Sami Tolvanen <samitolvanen@...gle.com>,
 Daniel Gomez <da.gomez@...sung.com>, linux-modules@...r.kernel.org
Subject: Re: [PATCH 5/8] module: Add module_for_each_mod() function

On Wed, 05 Feb 2025 17:50:36 -0500
Steven Rostedt <rostedt@...dmis.org> wrote:

> From: Steven Rostedt <rostedt@...dmis.org>
> 
> The tracing system needs a way to save all the currently loaded modules
> and their addresses into persistent memory so that it can evaluate the
> addresses on a reboot from a crash. When the persistent memory trace
> starts, it will load the module addresses and names into the persistent
> memory. To do so, it will call the module_for_each_mod() function and pass
> it a function and data structure to get called on each loaded module. Then
> it can record the memory.
> 
> This only implements that function.
> 
> Cc: Luis Chamberlain <mcgrof@...nel.org>
> Cc: Petr Pavlu <petr.pavlu@...e.com>
> Cc: Sami Tolvanen <samitolvanen@...gle.com>
> Cc: Daniel Gomez <da.gomez@...sung.com>
> Cc: linux-modules@...r.kernel.org
> Signed-off-by: Steven Rostedt (Google) <rostedt@...dmis.org>
> ---
>  include/linux/module.h |  6 ++++++
>  kernel/module/main.c   | 14 ++++++++++++++
>  2 files changed, 20 insertions(+)
> 
> diff --git a/include/linux/module.h b/include/linux/module.h
> index 23792d5d7b74..9e1f42f03511 100644
> --- a/include/linux/module.h
> +++ b/include/linux/module.h
> @@ -779,6 +779,8 @@ static inline void *module_writable_address(struct module *mod, void *loc)
>  	return __module_writable_address(mod, loc);
>  }
>  
> +void module_for_each_mod(int(*func)(struct module *mod, void *data), void *data);
> +
>  #else /* !CONFIG_MODULES... */
>  
>  static inline struct module *__module_address(unsigned long addr)
> @@ -891,6 +893,10 @@ static inline void *module_writable_address(struct module *mod, void *loc)
>  {
>  	return loc;
>  }
> +
> +static inline void module_for_each_mod(int(*func)(struct module *mod, void *data), void *data)
> +{
> +}
>  #endif /* CONFIG_MODULES */
>  
>  #ifdef CONFIG_SYSFS
> diff --git a/kernel/module/main.c b/kernel/module/main.c
> index 1fb9ad289a6f..ea1fe313fb89 100644
> --- a/kernel/module/main.c
> +++ b/kernel/module/main.c
> @@ -3809,6 +3809,20 @@ bool is_module_text_address(unsigned long addr)
>  	return ret;
>  }
>  

It is better to add a kerneldoc for this API.

/** 
 * module_for_each_mod() - iterate all modules
 * @func: Callback function
 * @data: User data
 *
 * Call the @func with each module in the system. If @func returns !0, this
 * stops itrating. Note that @func must not sleep since it is called under
 * the preemption disabled.
 */

BTW, do we really need to disable preempt or is it enough to call
rcu_read_lock()?

Thank you,

> +void module_for_each_mod(int(*func)(struct module *mod, void *data), void *data)
> +{
> +	struct module *mod;
> +
> +	preempt_disable();
> +	list_for_each_entry_rcu(mod, &modules, list) {
> +		if (mod->state == MODULE_STATE_UNFORMED)
> +			continue;
> +		if (func(mod, data))
> +			break;
> +	}
> +	preempt_enable();
> +}
> +
>  /**
>   * __module_text_address() - get the module whose code contains an address.
>   * @addr: the address.
> -- 
> 2.45.2
> 
> 


-- 
Masami Hiramatsu (Google) <mhiramat@...nel.org>