Commit 68007289 authored by Petr Mladek's avatar Petr Mladek Committed by Jiri Kosina
Browse files

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: default avatarPetr Mladek <pmladek@suse.com>
Acked-by: default avatarJoe Lawrence <joe.lawrence@redhat.com>
Acked-by: default avatarMiroslav Benes <mbenes@suse.cz>
Acked-by: default avatarJosh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: default avatarJiri Kosina <jkosina@suse.cz>
parent 0430f78b

include/linux/livepatch.h

+2 −0
Original line number Diff line number Diff line
@@ -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;

};

kernel/livepatch/core.c

+3 −1
Original line number Diff line number Diff line
@@ -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) {

kernel/livepatch/core.h

+1 −0
Original line number Diff line number Diff line
@@ -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)

{

kernel/livepatch/transition.c

+5 −5
Original line number Diff line number Diff line
@@ -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;

}

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