[PATCH v4 2/2] livepatch: force transition to finish
From: Miroslav Benes
Date: Wed Nov 15 2017 - 08:50:46 EST
If a task sleeps in a set of patched functions uninterruptedly, it could
block the whole transition 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 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! Administrator should not use this feature without a
clearance from a patch distributor. It must be checked that by doing so
the consistency model guarantees are not violated.
Signed-off-by: Miroslav Benes <mbenes@xxxxxxx>
---
Pavel, does this wording work for you?
Documentation/ABI/testing/sysfs-kernel-livepatch | 13 ++++++++++
Documentation/livepatch/livepatch.txt | 15 ++++++++++--
kernel/livepatch/core.c | 30 ++++++++++++++++++++++++
kernel/livepatch/transition.c | 25 ++++++++++++++++++++
kernel/livepatch/transition.h | 1 +
5 files changed, 82 insertions(+), 2 deletions(-)
diff --git a/Documentation/ABI/testing/sysfs-kernel-livepatch b/Documentation/ABI/testing/sysfs-kernel-livepatch
index 3bb9d5bc1ce3..567a8ebb795d 100644
--- a/Documentation/ABI/testing/sysfs-kernel-livepatch
+++ b/Documentation/ABI/testing/sysfs-kernel-livepatch
@@ -45,6 +45,19 @@ Contact: live-patching@xxxxxxxxxxxxxxx
signal pending structures). Tasks are interrupted or woken up,
and forced to change their patched state.
+What: /sys/kernel/livepatch/<patch>/force
+Date: Nov 2017
+KernelVersion: 4.15.0
+Contact: live-patching@xxxxxxxxxxxxxxx
+Description:
+ A writable attribute that allows administrator to affect the
+ course of an existing transition. Writing 1 clears
+ TIF_PATCH_PENDING flag of all tasks and thus forces the tasks to
+ the patched or unpatched state. Administrator should not
+ use this feature without a clearance from a patch
+ distributor. See Documentation/livepatch/livepatch.txt
+ for more information.
+
What: /sys/kernel/livepatch/<patch>/<object>
Date: Nov 2014
KernelVersion: 3.19.0
diff --git a/Documentation/livepatch/livepatch.txt b/Documentation/livepatch/livepatch.txt
index 9bcdef277a36..57d59274101d 100644
--- a/Documentation/livepatch/livepatch.txt
+++ b/Documentation/livepatch/livepatch.txt
@@ -183,6 +183,17 @@ tasks. No proper signal is actually delivered (there is no data in signal
pending structures). Tasks are interrupted or woken up, and forced to change
their patched state.
+Administrator can also affect a transition through
+/sys/kernel/livepatch/<patch>/force attribute. Writing 1 there clears
+TIF_PATCH_PENDING flag of all tasks and thus forces the tasks to the patched
+state. Important note! The force attribute is intended for cases when the
+transition gets stuck for a long time because of a blocking task. Administrator
+is expected to collect all necessary data (namely stack traces of such blocking
+tasks) and request a clearance from a patch distributor to force the transition.
+Unauthorized usage may cause harm to the system. It depends on the nature of the
+patch, which functions are (un)patched, and which functions the blocking tasks
+are sleeping in (/proc/<pid>/stack may help here).
+
3.1 Adding consistency model support to new architectures
---------------------------------------------------------
@@ -439,8 +450,8 @@ Information about the registered patches can be found under
/sys/kernel/livepatch. The patches could be enabled and disabled
by writing there.
-/sys/kernel/livepatch/<patch>/signal attribute allows administrator to affect a
-patching operation.
+/sys/kernel/livepatch/<patch>/signal and /sys/kernel/livepatch/<patch>/force
+attributes allow administrator to affect a patching operation.
See Documentation/ABI/testing/sysfs-kernel-livepatch for more details.
diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c
index e772be452462..c19c6c32c47e 100644
--- a/kernel/livepatch/core.c
+++ b/kernel/livepatch/core.c
@@ -441,6 +441,7 @@ EXPORT_SYMBOL_GPL(klp_enable_patch);
* /sys/kernel/livepatch/<patch>/enabled
* /sys/kernel/livepatch/<patch>/transition
* /sys/kernel/livepatch/<patch>/signal
+ * /sys/kernel/livepatch/<patch>/force
* /sys/kernel/livepatch/<patch>/<object>
* /sys/kernel/livepatch/<patch>/<object>/<function,sympos>
*/
@@ -542,13 +543,42 @@ static ssize_t signal_store(struct kobject *kobj, struct kobj_attribute *attr,
return count;
}
+static ssize_t force_store(struct kobject *kobj, struct kobj_attribute *attr,
+ const char *buf, size_t count)
+{
+ struct klp_patch *patch;
+ int ret;
+ bool val;
+
+ patch = container_of(kobj, struct klp_patch, kobj);
+
+ /*
+ * klp_mutex lock is not grabbed here intentionally. It is not really
+ * needed. The race window is harmless and grabbing the lock would only
+ * hold the action back.
+ */
+ if (patch != klp_transition_patch)
+ return -EINVAL;
+
+ ret = kstrtobool(buf, &val);
+ if (ret)
+ return ret;
+
+ if (val)
+ klp_force_transition();
+
+ return count;
+}
+
static struct kobj_attribute enabled_kobj_attr = __ATTR_RW(enabled);
static struct kobj_attribute transition_kobj_attr = __ATTR_RO(transition);
static struct kobj_attribute signal_kobj_attr = __ATTR_WO(signal);
+static struct kobj_attribute force_kobj_attr = __ATTR_WO(force);
static struct attribute *klp_patch_attrs[] = {
&enabled_kobj_attr.attr,
&transition_kobj_attr.attr,
&signal_kobj_attr.attr,
+ &force_kobj_attr.attr,
NULL
};
diff --git a/kernel/livepatch/transition.c b/kernel/livepatch/transition.c
index 095aa8d864f5..566ab210853f 100644
--- a/kernel/livepatch/transition.c
+++ b/kernel/livepatch/transition.c
@@ -618,3 +618,28 @@ void klp_send_signals(void)
}
read_unlock(&tasklist_lock);
}
+
+/*
+ * Drop TIF_PATCH_PENDING of all tasks on admin's request. This forces an
+ * existing transition to finish.
+ *
+ * NOTE: klp_update_patch_state(task) requires the task to be inactive or
+ * 'current'. This is not the case here and the consistency model could be
+ * broken. Administrator, who is the only one to execute the
+ * klp_force_transitions(), has to be aware of this.
+ */
+void klp_force_transition(void)
+{
+ struct task_struct *g, *task;
+ unsigned int cpu;
+
+ pr_warn("forcing remaining tasks to the patched state\n");
+
+ read_lock(&tasklist_lock);
+ for_each_process_thread(g, task)
+ klp_update_patch_state(task);
+ read_unlock(&tasklist_lock);
+
+ for_each_possible_cpu(cpu)
+ klp_update_patch_state(idle_task(cpu));
+}
diff --git a/kernel/livepatch/transition.h b/kernel/livepatch/transition.h
index 47c335f7c04c..837e51ee30fd 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_signals(void);
+void klp_force_transition(void);
#endif /* _LIVEPATCH_TRANSITION_H */
--
2.15.0