On Tue 2021-11-02 22:59:30, Ming Lei wrote:
> The completion finish is just for waiting release of the klp_patch
> object, then releases module refcnt. We can simply drop the module
> refcnt in the kobject release handler of klp_patch.
>
> This way also helps to support allocating klp_patch from heap.
IMHO, this is wrong assumption. kobject_put() might do everyting
asynchronously, see:
kobject_put()
kobject_release()
INIT_DELAYED_WORK(&kobj->release, kobject_delayed_cleanup);
schedule_delayed_work(&kobj->release, delay);
asynchronously:
kobject_delayed_cleanup()
kobject_cleanup()
__kobject_del()
> Signed-off-by: Ming Lei <ming.lei@xxxxxxxxxx>
> ---
> include/linux/livepatch.h | 1 -
> kernel/livepatch/core.c | 12 +++---------
> 2 files changed, 3 insertions(+), 10 deletions(-)
>
> diff --git a/include/linux/livepatch.h b/include/linux/livepatch.h
> index 2614247a9781..9712818997c5 100644
> --- a/include/linux/livepatch.h
> +++ b/include/linux/livepatch.h
> @@ -170,7 +170,6 @@ struct klp_patch {
> bool enabled;
> bool forced;
> struct work_struct free_work;
> - struct completion finish;
> };
>
> #define klp_for_each_object_static(patch, obj) \
> diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c
> index 335d988bd811..b967b4b0071b 100644
> --- a/kernel/livepatch/core.c
> +++ b/kernel/livepatch/core.c
> @@ -551,10 +551,10 @@ static int klp_add_nops(struct klp_patch *patch)
>
> static void klp_kobj_release_patch(struct kobject *kobj)
> {
> - struct klp_patch *patch;
> + struct klp_patch *patch = container_of(kobj, struct klp_patch, kobj);
>
> - patch = container_of(kobj, struct klp_patch, kobj);
> - complete(&patch->finish);
> + if (!patch->forced)
> + module_put(patch->mod);
> }
>
> static struct kobj_type klp_ktype_patch = {
> @@ -678,11 +678,6 @@ static void klp_free_patch_finish(struct klp_patch *patch)
> * cannot get enabled again.
> */
> kobject_put(&patch->kobj);
> - wait_for_completion(&patch->finish);
> -
> - /* Put the module after the last access to struct klp_patch. */
> - if (!patch->forced)
> - module_put(patch->mod);
klp_free_patch_finish() does not longer wait until the release
callbacks are called.
klp_free_patch_finish() is called also in klp_enable_patch() error
path.
klp_enable_patch() is called in module_init(). For example, see
samples/livepatch/livepatch-sample.c
The module must not get removed until the release callbacks are called.
Does the module loader check the module reference counter when
module_init() fails?
Best Regards,
Petr
