Re: [PATCH 3/7] module: take rcu_read_lock_sched for find_module

From: Eric Dumazet
Date: Thu Mar 15 2012 - 12:29:08 EST


On Thu, 2012-03-15 at 22:48 +0800, Cong Wang wrote:
> Similar to find_symbol(), find_module() also iterates module list,
> should use list_for_each_entry_rcu() too, thus its callers should
> hold rcu_read_lock_sched before calling it.
>
> Cc: Eric Dumazet <eric.dumazet@xxxxxxxxx>
> Cc: "Paul E. McKenney" <paulmck@xxxxxxxxxxxxxxxxxx>
> Cc: Rusty Russell <rusty@xxxxxxxxxxxxxxx>
> Signed-off-by: Cong Wang <xiyou.wangcong@xxxxxxxxx>
> ---
> kernel/module.c | 42 +++++++++++++++++++++++-------------------
> 1 files changed, 23 insertions(+), 19 deletions(-)
>
> diff --git a/kernel/module.c b/kernel/module.c
> index b31b23f..f210d74 100644
> --- a/kernel/module.c
> +++ b/kernel/module.c
> @@ -413,7 +413,7 @@ struct module *find_module(const char *name)
> {
> struct module *mod;
>
> - list_for_each_entry(mod, &modules, list) {
> + list_for_each_entry_rcu(mod, &modules, list) {
> if (strcmp(mod->name, name) == 0)
> return mod;
> }
> @@ -778,14 +778,16 @@ SYSCALL_DEFINE2(delete_module, const char __user *, name_user,
> return -EFAULT;
> name[MODULE_NAME_LEN-1] = '\0';
>
> - if (mutex_lock_interruptible(&module_mutex) != 0)
> - return -EINTR;
> -
> + rcu_read_lock_sched();
> mod = find_module(name);
> if (!mod) {
> - ret = -ENOENT;
> - goto out;
> + rcu_read_unlock_sched();
> + return -ENOENT;
> }
> + rcu_read_unlock_sched();
> +

Thats a bug.

> + if (mutex_lock_interruptible(&module_mutex) != 0)
> + return -EINTR;

mod might already had disappear.

>
> if (!list_empty(&mod->source_list)) {
> /* Other modules depend on us: get rid of them first. */


--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/