Re: [PATCH 1/2] livepatch: Remove custom kobject state handling

[Greg Kroah-Hartman]

On Tue, May 07, 2019 at 02:32:57PM +0200, Miroslav Benes wrote:
> On Fri, 3 May 2019, Petr Mladek wrote:
> 
> > kobject_init() always succeeds and sets the reference count to 1.
> > It allows to always free the structures via kobject_put() and
> > the related release callback.
> > 
> > Note that the custom kobject state handling was used only
> > because we did not know that kobject_put() can and actually
> > should get called even when kobject_init_and_add() fails.
> > 
> > The patch should not change the existing behavior.
> 
> Pity that the changelog does not describe the change from 
> kobject_init_and_add() to two-stage kobject init (separate kobject_init() 
> and kobject_add()).
> 
> Petr changed it, because now each member of new dynamic lists (created in 
> klp_init_patch_early()) is initialized with kobject_init(), so we do not 
> have to worry about calling kobject_put() (this is slightly different from 
> kobj_added).
> 
> It would also be possible to retain kobject_init_and_add() and move it to 
> klp_init_patch_early(), but it would be uglier in my opinion.

kobject_init_and_add() is only there for the "simple" use cases.
There's no problem with doing the two-stage process on your own like
this, that's exactly what it is there for :)

thanks,

greg k-h

Re: [PATCH 1/2] livepatch: Remove custom kobject state handling

[Miroslav Benes]

On Fri, 3 May 2019, Petr Mladek wrote:

> kobject_init() always succeeds and sets the reference count to 1.
> It allows to always free the structures via kobject_put() and
> the related release callback.
> 
> Note that the custom kobject state handling was used only
> because we did not know that kobject_put() can and actually
> should get called even when kobject_init_and_add() fails.
> 
> The patch should not change the existing behavior.

Pity that the changelog does not describe the change from 
kobject_init_and_add() to two-stage kobject init (separate kobject_init() 
and kobject_add()).

Petr changed it, because now each member of new dynamic lists (created in 
klp_init_patch_early()) is initialized with kobject_init(), so we do not 
have to worry about calling kobject_put() (this is slightly different from 
kobj_added).

It would also be possible to retain kobject_init_and_add() and move it to 
klp_init_patch_early(), but it would be uglier in my opinion.

Miroslav

Re: [PATCH 1/2] livepatch: Remove custom kobject state handling

[Kamalesh Babulal]

On Fri, May 03, 2019 at 03:26:24PM +0200, Petr Mladek wrote:
> kobject_init() always succeeds and sets the reference count to 1.
> It allows to always free the structures via kobject_put() and
> the related release callback.
> 
> Note that the custom kobject state handling was used only
> because we did not know that kobject_put() can and actually
> should get called even when kobject_init_and_add() fails.
> 
> The patch should not change the existing behavior.
> 
> Suggested-by: "Tobin C. Harding" 
> Signed-off-by: Petr Mladek 
> ---
>  include/linux/livepatch.h |  3 ---
>  kernel/livepatch/core.c   | 56 
> ++-
>  2 files changed, 17 insertions(+), 42 deletions(-)
> 
> diff --git a/include/linux/livepatch.h b/include/linux/livepatch.h
> index 53551f470722..a14bab1a0a3e 100644
> --- a/include/linux/livepatch.h
> +++ b/include/linux/livepatch.h
> @@ -86,7 +86,6 @@ struct klp_func {
>   struct list_head node;
>   struct list_head stack_node;
>   unsigned long old_size, new_size;
> - bool kobj_added;
>   bool nop;
>   bool patched;
>   bool transition;

Minor nitpick, the description of kobj_added needs to be removed from
structure descriptions. 

Reviewed-by: Kamalesh Babulal 

-- 
Kamalesh

[PATCH 1/2] livepatch: Remove custom kobject state handling

[Petr Mladek]

kobject_init() always succeeds and sets the reference count to 1.
It allows to always free the structures via kobject_put() and
the related release callback.

Note that the custom kobject state handling was used only
because we did not know that kobject_put() can and actually
should get called even when kobject_init_and_add() fails.

The patch should not change the existing behavior.

Suggested-by: "Tobin C. Harding" 
Signed-off-by: Petr Mladek 
---
 include/linux/livepatch.h |  3 ---
 kernel/livepatch/core.c   | 56 ++-
 2 files changed, 17 insertions(+), 42 deletions(-)

diff --git a/include/linux/livepatch.h b/include/linux/livepatch.h
index 53551f470722..a14bab1a0a3e 100644
--- a/include/linux/livepatch.h
+++ b/include/linux/livepatch.h
@@ -86,7 +86,6 @@ struct klp_func {
struct list_head node;
struct list_head stack_node;
unsigned long old_size, new_size;
-   bool kobj_added;
bool nop;
bool patched;
bool transition;
@@ -141,7 +140,6 @@ struct klp_object {
struct list_head func_list;
struct list_head node;
struct module *mod;
-   bool kobj_added;
bool dynamic;
bool patched;
 };
@@ -170,7 +168,6 @@ struct klp_patch {
struct list_head list;
struct kobject kobj;
struct list_head obj_list;
-   bool kobj_added;
bool enabled;
bool forced;
struct work_struct free_work;
diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c
index eb0ee10a1981..1ff91f7cbafb 100644
--- a/kernel/livepatch/core.c
+++ b/kernel/livepatch/core.c
@@ -426,6 +426,9 @@ static void klp_free_object_dynamic(struct klp_object *obj)
kfree(obj);
 }
 
+static struct kobj_type klp_ktype_object;
+static struct kobj_type klp_ktype_func;
+
 static struct klp_object *klp_alloc_object_dynamic(const char *name)
 {
struct klp_object *obj;
@@ -443,6 +446,7 @@ static struct klp_object *klp_alloc_object_dynamic(const 
char *name)
}
 
INIT_LIST_HEAD(&obj->func_list);
+   kobject_init(&obj->kobj, &klp_ktype_object);
obj->dynamic = true;
 
return obj;
@@ -471,6 +475,7 @@ static struct klp_func *klp_alloc_func_nop(struct klp_func 
*old_func,
}
}
 
+   kobject_init(&func->kobj, &klp_ktype_func);
/*
 * func->new_func is same as func->old_func. These addresses are
 * set when the object is loaded, see klp_init_object_loaded().
@@ -588,13 +593,7 @@ static void __klp_free_funcs(struct klp_object *obj, bool 
nops_only)
continue;
 
list_del(&func->node);
-
-   /* Might be called from klp_init_patch() error path. */
-   if (func->kobj_added) {
-   kobject_put(&func->kobj);
-   } else if (func->nop) {
-   klp_free_func_nop(func);
-   }
+   kobject_put(&func->kobj);
}
 }
 
@@ -624,13 +623,7 @@ static void __klp_free_objects(struct klp_patch *patch, 
bool nops_only)
continue;
 
list_del(&obj->node);
-
-   /* Might be called from klp_init_patch() error path. */
-   if (obj->kobj_added) {
-   kobject_put(&obj->kobj);
-   } else if (obj->dynamic) {
-   klp_free_object_dynamic(obj);
-   }
+   kobject_put(&obj->kobj);
}
 }
 
@@ -675,10 +668,8 @@ static void klp_free_patch_finish(struct klp_patch *patch)
 * this is called when the patch gets disabled and it
 * cannot get enabled again.
 */
-   if (patch->kobj_added) {
-   kobject_put(&patch->kobj);
-   wait_for_completion(&patch->finish);
-   }
+   kobject_put(&patch->kobj);
+   wait_for_completion(&patch->finish);
 
/* Put the module after the last access to struct klp_patch. */
if (!patch->forced)
@@ -700,8 +691,6 @@ static void klp_free_patch_work_fn(struct work_struct *work)
 
 static int klp_init_func(struct klp_object *obj, struct klp_func *func)
 {
-   int ret;
-
if (!func->old_name)
return -EINVAL;
 
@@ -724,13 +713,9 @@ static int klp_init_func(struct klp_object *obj, struct 
klp_func *func)
 * object. If the user selects 0 for old_sympos, then 1 will be used
 * since a unique symbol will be the first occurrence.
 */
-   ret = kobject_init_and_add(&func->kobj, &klp_ktype_func,
-  &obj->kobj, "%s,%lu", func->old_name,
-  func->old_sympos ? func->old_sympos : 1);
-   if (!ret)
-   func->kobj_added = true;
-
-   return ret;
+   return kobject_add(&func->kobj, &obj->kobj, "%s,%lu",
+  func->old_name,
+  func->old_sympos ? func->old_sympos : 1);
 }
 
 /* Arches may ov