Re: [PATCH] livepatch: fix race between enabled_store() and klp_unregister_patch()

Jiri Slaby
2015-12-01T14:28:24Z

On 12/01/2015, 03:13 PM, Petr Mladek wrote:
> --- a/kernel/livepatch/core.c
> +++ b/kernel/livepatch/core.c
> @@ -612,7 +612,19 @@ static ssize_t enabled_store(struct kobject *kobj, struct kobj_attribute *attr,
>
> patch = container_of(kobj, struct klp_patch, kobj);
>
> - mutex_lock(&klp_mutex);
> + /*
> + * Avoid a deadlock with kobject_put(&patch->kobj) that is
> + * called under klp_mutex. Bail out when the patch is not
> + * longer registered.
> + */
> + if (!mutex_trylock(&klp_mutex)) {

This introduces false positives.
Deleting/enabling/disabling/other_op_under_klp_mutex of an unrelated
patch may now cause enabled_store to fail. Hence I don't like this
approach at all.

thanks,
--
js
suse labs