linux-kernel - Re: [PATCH 2/6] module: use list_for_each_entry_rcu() on find_module

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Date:   Tue, 23 May 2017 16:46:31 +0200 (CEST)
From:   Miroslav Benes <mbenes@...e.cz>
To:     "Luis R. Rodriguez" <mcgrof@...nel.org>
cc:     shuah@...nel.org, jeyu@...hat.com, rusty@...tcorp.com.au,
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Subject: Re: [PATCH 2/6] module: use list_for_each_entry_rcu() on
 find_module_all()

On Thu, 18 May 2017, Luis R. Rodriguez wrote:

> The module list has been using RCU in a lot of other calls
> for a while now, we just overlooked changing this one over to
> use RCU.
> 
> Signed-off-by: Luis R. Rodriguez <mcgrof@...nel.org>
> ---
>  kernel/module.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/module.c b/kernel/module.c
> index 4a3665f8f837..70f494638974 100644
> --- a/kernel/module.c
> +++ b/kernel/module.c
> @@ -602,7 +602,7 @@ static struct module *find_module_all(const char *name, size_t len,
>  
>  	module_assert_mutex_or_preempt();
>  
> -	list_for_each_entry(mod, &modules, list) {
> +	list_for_each_entry_rcu(mod, &modules, list) {
>  		if (!even_unformed && mod->state == MODULE_STATE_UNFORMED)
>  			continue;
>  		if (strlen(mod->name) == len && !memcmp(mod->name, name, len))

This makes sense. It would not be an issue if all callers of 
find_module_all() held module_mutex, but module_kallsyms_lookup_name() 
does not.

There is one more occurrence of just list_for_each_entry(mod, &modules, 
list) in kernel/module.c -- in module_kallsyms_on_each_symbol(). But that 
one is safe because we have to hold the mutex there.

Miroslav