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livepatch: Don't block the removal of patches loaded after a forced transition 

module_put() is currently never called in klp_complete_transition() when
klp_force is set. As a result, we might keep the reference count even when
klp_enable_patch() fails and klp_cancel_transition() is called.

This might give the impression that a module might get blocked in some
strange init state. Fortunately, it is not the case. The reference count
is ignored when mod->init fails and erroneous modules are always removed.

Anyway, this might be confusing. Instead, this patch moves
the global klp_forced flag into struct klp_patch. As a result,
we block only modules that might still be in use after a forced
transition. Newly loaded livepatches might be eventually completely
removed later.

It is not a big deal. But the code is at least consistent with
the reality.

Signed-off-by: Petr Mladek <pmladek@suse.com>
Acked-by: Joe Lawrence <joe.lawrence@redhat.com>
Acked-by: Miroslav Benes <mbenes@suse.cz>
Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
This commit is contained in:
Petr Mladek 2019-01-09 13:43:22 +01:00 committed by Jiri Kosina
parent 0430f78bf3
commit 68007289bf
4 changed files with 11 additions and 6 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
include/linux/livepatch.h
View File

@ -143,6 +143,7 @@ struct klp_object {
* @kobj: kobject for sysfs resources
* @kobj_added: @kobj has been added and needs freeing
* @enabled: the patch is enabled (but operation may be incomplete)
* @forced: was involved in a forced transition
* @finish: for waiting till it is safe to remove the patch module
*/
struct klp_patch {
@ -155,6 +156,7 @@ struct klp_patch {
struct kobject kobj;
bool kobj_added;
bool enabled;
bool forced;
struct completion finish;
};

4
kernel/livepatch/core.c
View File

@ -45,7 +45,8 @@
*/
DEFINE_MUTEX(klp_mutex);
static LIST_HEAD(klp_patches);
/* Registered patches */
LIST_HEAD(klp_patches);
static struct kobject *klp_root_kobj;
@ -659,6 +660,7 @@ static int klp_init_patch_early(struct klp_patch *patch)
INIT_LIST_HEAD(&patch->list);
patch->kobj_added = false;
patch->enabled = false;
patch->forced = false;
init_completion(&patch->finish);
klp_for_each_object(patch, obj) {

1
kernel/livepatch/core.h
View File

@ -5,6 +5,7 @@
#include <linux/livepatch.h>
extern struct mutex klp_mutex;
extern struct list_head klp_patches;
static inline bool klp_is_object_loaded(struct klp_object *obj)
{

10
kernel/livepatch/transition.c
View File

@ -33,8 +33,6 @@ struct klp_patch *klp_transition_patch;
static int klp_target_state = KLP_UNDEFINED;
static bool klp_forced = false;
/*
* This work can be performed periodically to finish patching or unpatching any
* "straggler" tasks which failed to transition in the first attempt.
@ -137,10 +135,10 @@ static void klp_complete_transition(void)
klp_target_state == KLP_PATCHED ? "patching" : "unpatching");
/*
* klp_forced set implies unbounded increase of module's ref count if
* patch->forced set implies unbounded increase of module's ref count if
* the module is disabled/enabled in a loop.
*/
if (!klp_forced && klp_target_state == KLP_UNPATCHED)
if (!klp_transition_patch->forced && klp_target_state == KLP_UNPATCHED)
module_put(klp_transition_patch->mod);
klp_target_state = KLP_UNDEFINED;
@ -620,6 +618,7 @@ void klp_send_signals(void)
*/
void klp_force_transition(void)
{
struct klp_patch *patch;
struct task_struct *g, *task;
unsigned int cpu;
@ -633,5 +632,6 @@ void klp_force_transition(void)
for_each_possible_cpu(cpu)
klp_update_patch_state(idle_task(cpu));
klp_forced = true;
list_for_each_entry(patch, &klp_patches, list)
patch->forced = true;
}