Re: [PATCH 2/6] module: use list_for_each_entry_rcu() on find_module_all()

Miroslav Benes
2017-05-23T14:46:39Z

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@kernel.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