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SubjectRe: [PATCH 4/8] livepatch: Add an extra flag to distinguish registered patches
On Fri, 23 Mar 2018, Petr Mladek wrote:

> The initial implementation of the atomic replace feature keeps the replaced
> patches on the stack. But people would like to remove the replaced patches
> from different reasons that will be described in the following patch.
>
> This patch is just a small preparation step. We will need to keep
> the replaced patches registered even when they are not longer on the stack.

s/not longer/no longer/

> It is because they are typically unregistered by the module exit script.
>
> Therefore we need to detect the registered patches another way.

"in another way", "differently"?

> We could
> not use kobj.state_initialized because it is racy. The kobject is destroyed
> by an asynchronous call and could not be synchronized using klp_mutex.
>
> This patch solves the problem by adding a flag into struct klp_patch.
> It is manipulated under klp_mutex and therefore it is safe. It is easy
> to understand and it is enough in most situations.
>
> The function klp_is_patch_registered() is not longer needed. Though

s/not longer/no longer/

s/Though/So/ ?

> it was renamed to klp_is_patch_on_stack() and used in __klp_enable_patch()
> as a new sanity check.
>
> This patch does not change the existing behavior.

In my opinion it could be easier for a review to squash the patch into the
next one.

> Signed-off-by: Petr Mladek <pmladek@suse.com>
> Cc: Josh Poimboeuf <jpoimboe@redhat.com>
> Cc: Jessica Yu <jeyu@kernel.org>
> Cc: Jiri Kosina <jikos@kernel.org>
> Cc: Miroslav Benes <mbenes@suse.cz>
> Cc: Jason Baron <jbaron@akamai.com>
> ---
> include/linux/livepatch.h | 2 ++
> kernel/livepatch/core.c | 24 ++++++++++++++++++------
> 2 files changed, 20 insertions(+), 6 deletions(-)
>
> diff --git a/include/linux/livepatch.h b/include/linux/livepatch.h
> index f28af280f9e0..d6e6d8176995 100644
> --- a/include/linux/livepatch.h
> +++ b/include/linux/livepatch.h
> @@ -150,6 +150,7 @@ struct klp_object {
> * @list: list node for global list of registered patches
> * @kobj: kobject for sysfs resources
> * @obj_list: dynamic list of the object entries
> + * @registered: reliable way to check registration status
> * @enabled: the patch is enabled (but operation may be incomplete)
> * @finish: for waiting till it is safe to remove the patch module
> */
> @@ -163,6 +164,7 @@ struct klp_patch {
> struct list_head list;
> struct kobject kobj;
> struct list_head obj_list;
> + bool registered;
> bool enabled;
> struct completion finish;
> };
> diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c
> index 18c400bd9a33..70c67a834e9a 100644
> --- a/kernel/livepatch/core.c
> +++ b/kernel/livepatch/core.c
> @@ -45,6 +45,11 @@
> */
> DEFINE_MUTEX(klp_mutex);
>
> +/*
> + * Stack of patches. It defines the order in which the patches can be enabled.
> + * Only patches on this stack might be enabled. New patches are added when
> + * registered. They are removed when they are unregistered.
> + */
> static LIST_HEAD(klp_patches);
>
> static struct kobject *klp_root_kobj;
> @@ -97,7 +102,7 @@ static void klp_find_object_module(struct klp_object *obj)
> mutex_unlock(&module_mutex);
> }
>
> -static bool klp_is_patch_registered(struct klp_patch *patch)
> +static bool klp_is_patch_on_stack(struct klp_patch *patch)
> {
> struct klp_patch *mypatch;
>
> @@ -378,7 +383,7 @@ int klp_disable_patch(struct klp_patch *patch)
>
> mutex_lock(&klp_mutex);
>
> - if (!klp_is_patch_registered(patch)) {
> + if (!patch->registered) {

I don't see any actual problem, but I'd feel safer if we preserve
klp_is_patch_on_stack() even somewhere in disable path.

Miroslav

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