[PATCH 3/3] livepatch: force transition process to finish

[Miroslav Benes <mbenes@suse.cz>]

If a task sleeps in a set of patched functions uninterruptibly, it could
block the whole transition process indefinitely.  Thus it may be useful
to clear its TIF_PATCH_PENDING to allow the process to finish.

Admin can do that now by writing 2 to force sysfs attribute in livepatch
sysfs directory. TIF_PATCH_PENDING is then cleared for all tasks and the
transition can finish successfully.

Important note! Use wisely. Admin must be sure that it is safe to
execute such action. This means that it must be checked that by doing so
the consistency model guarantees are not violated.

Signed-off-by: Miroslav Benes <mbenes@suse.cz>
---
 include/linux/livepatch.h     |  1 +
 kernel/livepatch/core.c       |  3 +++
 kernel/livepatch/transition.c | 16 ++++++++++++++++
 kernel/livepatch/transition.h |  1 +
 4 files changed, 21 insertions(+)

diff --git a/include/linux/livepatch.h b/include/linux/livepatch.h
index 43cfeebeb42b..b567208a1c6e 100644
--- a/include/linux/livepatch.h
+++ b/include/linux/livepatch.h
@@ -31,6 +31,7 @@
 
 /* values for sysfs force attribute */
 #define KLP_FORCE_FAKE		1
+#define KLP_FORCE_UNMARK	2
 
 /* task patch states */
 #define KLP_UNDEFINED	-1
diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c
index bb3b78fa7d2b..9bc1103348c9 100644
--- a/kernel/livepatch/core.c
+++ b/kernel/livepatch/core.c
@@ -469,6 +469,9 @@ static ssize_t force_store(struct kobject *kobj, struct kobj_attribute *attr,
 	case KLP_FORCE_FAKE:
 		klp_send_fake_signal();
 		break;
+	case KLP_FORCE_UNMARK:
+		klp_unmark_tasks();
+		break;
 	default:
 		return -EINVAL;
 	}
diff --git a/kernel/livepatch/transition.c b/kernel/livepatch/transition.c
index bb61aaa196d3..d057a34510e6 100644
--- a/kernel/livepatch/transition.c
+++ b/kernel/livepatch/transition.c
@@ -591,3 +591,19 @@ void klp_send_fake_signal(void)
 	}
 	read_unlock(&tasklist_lock);
 }
+
+/*
+ * Drop TIF_PATCH_PENDING of all tasks on admin's request. This forces an
+ * existing transition to finish.
+ */
+void klp_unmark_tasks(void)
+{
+	struct task_struct *g, *task;
+
+	pr_warn("all tasks marked as migrated on admin's request\n");
+
+	read_lock(&tasklist_lock);
+	for_each_process_thread(g, task)
+		klp_update_patch_state(task);
+	read_unlock(&tasklist_lock);
+}
diff --git a/kernel/livepatch/transition.h b/kernel/livepatch/transition.h
index 1c7ede6eaa77..c129397b3985 100644
--- a/kernel/livepatch/transition.h
+++ b/kernel/livepatch/transition.h
@@ -11,5 +11,6 @@ void klp_start_transition(void);
 void klp_try_complete_transition(void);
 void klp_reverse_transition(void);
 void klp_send_fake_signal(void);
+void klp_unmark_tasks(void);
 
 #endif /* _LIVEPATCH_TRANSITION_H */
-- 
2.12.2