Adding upstream version 6.6.15.upstream/6.6.15

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 752 insertions, 0 deletions

diff --git a/kernel/livepatch/transition.c b/kernel/livepatch/transition.c
new file mode 100644
index 0000000000..e54c3d60a9
--- /dev/null
+++ b/kernel/livepatch/transition.c
@@ -0,0 +1,752 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * transition.c - Kernel Live Patching transition functions
+ *
+ * Copyright (C) 2015-2016 Josh Poimboeuf <jpoimboe@redhat.com>
+ */
+
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include <linux/cpu.h>
+#include <linux/stacktrace.h>
+#include <linux/static_call.h>
+#include "core.h"
+#include "patch.h"
+#include "transition.h"
+
+#define MAX_STACK_ENTRIES  100
+static DEFINE_PER_CPU(unsigned long[MAX_STACK_ENTRIES], klp_stack_entries);
+
+#define STACK_ERR_BUF_SIZE 128
+
+#define SIGNALS_TIMEOUT 15
+
+struct klp_patch *klp_transition_patch;
+
+static int klp_target_state = KLP_UNDEFINED;
+
+static unsigned int klp_signals_cnt;
+
+/*
+ * When a livepatch is in progress, enable klp stack checking in
+ * cond_resched().  This helps CPU-bound kthreads get patched.
+ */
+#if defined(CONFIG_PREEMPT_DYNAMIC) && defined(CONFIG_HAVE_PREEMPT_DYNAMIC_CALL)
+
+#define klp_cond_resched_enable() sched_dynamic_klp_enable()
+#define klp_cond_resched_disable() sched_dynamic_klp_disable()
+
+#else /* !CONFIG_PREEMPT_DYNAMIC || !CONFIG_HAVE_PREEMPT_DYNAMIC_CALL */
+
+DEFINE_STATIC_KEY_FALSE(klp_sched_try_switch_key);
+EXPORT_SYMBOL(klp_sched_try_switch_key);
+
+#define klp_cond_resched_enable() static_branch_enable(&klp_sched_try_switch_key)
+#define klp_cond_resched_disable() static_branch_disable(&klp_sched_try_switch_key)
+
+#endif /* CONFIG_PREEMPT_DYNAMIC && CONFIG_HAVE_PREEMPT_DYNAMIC_CALL */
+
+/*
+ * This work can be performed periodically to finish patching or unpatching any
+ * "straggler" tasks which failed to transition in the first attempt.
+ */
+static void klp_transition_work_fn(struct work_struct *work)
+{
+	mutex_lock(&klp_mutex);
+
+	if (klp_transition_patch)
+		klp_try_complete_transition();
+
+	mutex_unlock(&klp_mutex);
+}
+static DECLARE_DELAYED_WORK(klp_transition_work, klp_transition_work_fn);
+
+/*
+ * This function is just a stub to implement a hard force
+ * of synchronize_rcu(). This requires synchronizing
+ * tasks even in userspace and idle.
+ */
+static void klp_sync(struct work_struct *work)
+{
+}
+
+/*
+ * We allow to patch also functions where RCU is not watching,
+ * e.g. before user_exit(). We can not rely on the RCU infrastructure
+ * to do the synchronization. Instead hard force the sched synchronization.
+ *
+ * This approach allows to use RCU functions for manipulating func_stack
+ * safely.
+ */
+static void klp_synchronize_transition(void)
+{
+	schedule_on_each_cpu(klp_sync);
+}
+
+/*
+ * The transition to the target patch state is complete.  Clean up the data
+ * structures.
+ */
+static void klp_complete_transition(void)
+{
+	struct klp_object *obj;
+	struct klp_func *func;
+	struct task_struct *g, *task;
+	unsigned int cpu;
+
+	pr_debug("'%s': completing %s transition\n",
+		 klp_transition_patch->mod->name,
+		 klp_target_state == KLP_PATCHED ? "patching" : "unpatching");
+
+	if (klp_transition_patch->replace && klp_target_state == KLP_PATCHED) {
+		klp_unpatch_replaced_patches(klp_transition_patch);
+		klp_discard_nops(klp_transition_patch);
+	}
+
+	if (klp_target_state == KLP_UNPATCHED) {
+		/*
+		 * All tasks have transitioned to KLP_UNPATCHED so we can now
+		 * remove the new functions from the func_stack.
+		 */
+		klp_unpatch_objects(klp_transition_patch);
+
+		/*
+		 * Make sure klp_ftrace_handler() can no longer see functions
+		 * from this patch on the ops->func_stack.  Otherwise, after
+		 * func->transition gets cleared, the handler may choose a
+		 * removed function.
+		 */
+		klp_synchronize_transition();
+	}
+
+	klp_for_each_object(klp_transition_patch, obj)
+		klp_for_each_func(obj, func)
+			func->transition = false;
+
+	/* Prevent klp_ftrace_handler() from seeing KLP_UNDEFINED state */
+	if (klp_target_state == KLP_PATCHED)
+		klp_synchronize_transition();
+
+	read_lock(&tasklist_lock);
+	for_each_process_thread(g, task) {
+		WARN_ON_ONCE(test_tsk_thread_flag(task, TIF_PATCH_PENDING));
+		task->patch_state = KLP_UNDEFINED;
+	}
+	read_unlock(&tasklist_lock);
+
+	for_each_possible_cpu(cpu) {
+		task = idle_task(cpu);
+		WARN_ON_ONCE(test_tsk_thread_flag(task, TIF_PATCH_PENDING));
+		task->patch_state = KLP_UNDEFINED;
+	}
+
+	klp_for_each_object(klp_transition_patch, obj) {
+		if (!klp_is_object_loaded(obj))
+			continue;
+		if (klp_target_state == KLP_PATCHED)
+			klp_post_patch_callback(obj);
+		else if (klp_target_state == KLP_UNPATCHED)
+			klp_post_unpatch_callback(obj);
+	}
+
+	pr_notice("'%s': %s complete\n", klp_transition_patch->mod->name,
+		  klp_target_state == KLP_PATCHED ? "patching" : "unpatching");
+
+	klp_target_state = KLP_UNDEFINED;
+	klp_transition_patch = NULL;
+}
+
+/*
+ * This is called in the error path, to cancel a transition before it has
+ * started, i.e. klp_init_transition() has been called but
+ * klp_start_transition() hasn't.  If the transition *has* been started,
+ * klp_reverse_transition() should be used instead.
+ */
+void klp_cancel_transition(void)
+{
+	if (WARN_ON_ONCE(klp_target_state != KLP_PATCHED))
+		return;
+
+	pr_debug("'%s': canceling patching transition, going to unpatch\n",
+		 klp_transition_patch->mod->name);
+
+	klp_target_state = KLP_UNPATCHED;
+	klp_complete_transition();
+}
+
+/*
+ * Switch the patched state of the task to the set of functions in the target
+ * patch state.
+ *
+ * NOTE: If task is not 'current', the caller must ensure the task is inactive.
+ * Otherwise klp_ftrace_handler() might read the wrong 'patch_state' value.
+ */
+void klp_update_patch_state(struct task_struct *task)
+{
+	/*
+	 * A variant of synchronize_rcu() is used to allow patching functions
+	 * where RCU is not watching, see klp_synchronize_transition().
+	 */
+	preempt_disable_notrace();
+
+	/*
+	 * This test_and_clear_tsk_thread_flag() call also serves as a read
+	 * barrier (smp_rmb) for two cases:
+	 *
+	 * 1) Enforce the order of the TIF_PATCH_PENDING read and the
+	 *    klp_target_state read.  The corresponding write barriers are in
+	 *    klp_init_transition() and klp_reverse_transition().
+	 *
+	 * 2) Enforce the order of the TIF_PATCH_PENDING read and a future read
+	 *    of func->transition, if klp_ftrace_handler() is called later on
+	 *    the same CPU.  See __klp_disable_patch().
+	 */
+	if (test_and_clear_tsk_thread_flag(task, TIF_PATCH_PENDING))
+		task->patch_state = READ_ONCE(klp_target_state);
+
+	preempt_enable_notrace();
+}
+
+/*
+ * Determine whether the given stack trace includes any references to a
+ * to-be-patched or to-be-unpatched function.
+ */
+static int klp_check_stack_func(struct klp_func *func, unsigned long *entries,
+				unsigned int nr_entries)
+{
+	unsigned long func_addr, func_size, address;
+	struct klp_ops *ops;
+	int i;
+
+	if (klp_target_state == KLP_UNPATCHED) {
+		 /*
+		  * Check for the to-be-unpatched function
+		  * (the func itself).
+		  */
+		func_addr = (unsigned long)func->new_func;
+		func_size = func->new_size;
+	} else {
+		/*
+		 * Check for the to-be-patched function
+		 * (the previous func).
+		 */
+		ops = klp_find_ops(func->old_func);
+
+		if (list_is_singular(&ops->func_stack)) {
+			/* original function */
+			func_addr = (unsigned long)func->old_func;
+			func_size = func->old_size;
+		} else {
+			/* previously patched function */
+			struct klp_func *prev;
+
+			prev = list_next_entry(func, stack_node);
+			func_addr = (unsigned long)prev->new_func;
+			func_size = prev->new_size;
+		}
+	}
+
+	for (i = 0; i < nr_entries; i++) {
+		address = entries[i];
+
+		if (address >= func_addr && address < func_addr + func_size)
+			return -EAGAIN;
+	}
+
+	return 0;
+}
+
+/*
+ * Determine whether it's safe to transition the task to the target patch state
+ * by looking for any to-be-patched or to-be-unpatched functions on its stack.
+ */
+static int klp_check_stack(struct task_struct *task, const char **oldname)
+{
+	unsigned long *entries = this_cpu_ptr(klp_stack_entries);
+	struct klp_object *obj;
+	struct klp_func *func;
+	int ret, nr_entries;
+
+	/* Protect 'klp_stack_entries' */
+	lockdep_assert_preemption_disabled();
+
+	ret = stack_trace_save_tsk_reliable(task, entries, MAX_STACK_ENTRIES);
+	if (ret < 0)
+		return -EINVAL;
+	nr_entries = ret;
+
+	klp_for_each_object(klp_transition_patch, obj) {
+		if (!obj->patched)
+			continue;
+		klp_for_each_func(obj, func) {
+			ret = klp_check_stack_func(func, entries, nr_entries);
+			if (ret) {
+				*oldname = func->old_name;
+				return -EADDRINUSE;
+			}
+		}
+	}
+
+	return 0;
+}
+
+static int klp_check_and_switch_task(struct task_struct *task, void *arg)
+{
+	int ret;
+
+	if (task_curr(task) && task != current)
+		return -EBUSY;
+
+	ret = klp_check_stack(task, arg);
+	if (ret)
+		return ret;
+
+	clear_tsk_thread_flag(task, TIF_PATCH_PENDING);
+	task->patch_state = klp_target_state;
+	return 0;
+}
+
+/*
+ * Try to safely switch a task to the target patch state.  If it's currently
+ * running, or it's sleeping on a to-be-patched or to-be-unpatched function, or
+ * if the stack is unreliable, return false.
+ */
+static bool klp_try_switch_task(struct task_struct *task)
+{
+	const char *old_name;
+	int ret;
+
+	/* check if this task has already switched over */
+	if (task->patch_state == klp_target_state)
+		return true;
+
+	/*
+	 * For arches which don't have reliable stack traces, we have to rely
+	 * on other methods (e.g., switching tasks at kernel exit).
+	 */
+	if (!klp_have_reliable_stack())
+		return false;
+
+	/*
+	 * Now try to check the stack for any to-be-patched or to-be-unpatched
+	 * functions.  If all goes well, switch the task to the target patch
+	 * state.
+	 */
+	if (task == current)
+		ret = klp_check_and_switch_task(current, &old_name);
+	else
+		ret = task_call_func(task, klp_check_and_switch_task, &old_name);
+
+	switch (ret) {
+	case 0:		/* success */
+		break;
+
+	case -EBUSY:	/* klp_check_and_switch_task() */
+		pr_debug("%s: %s:%d is running\n",
+			 __func__, task->comm, task->pid);
+		break;
+	case -EINVAL:	/* klp_check_and_switch_task() */
+		pr_debug("%s: %s:%d has an unreliable stack\n",
+			 __func__, task->comm, task->pid);
+		break;
+	case -EADDRINUSE: /* klp_check_and_switch_task() */
+		pr_debug("%s: %s:%d is sleeping on function %s\n",
+			 __func__, task->comm, task->pid, old_name);
+		break;
+
+	default:
+		pr_debug("%s: Unknown error code (%d) when trying to switch %s:%d\n",
+			 __func__, ret, task->comm, task->pid);
+		break;
+	}
+
+	return !ret;
+}
+
+void __klp_sched_try_switch(void)
+{
+	if (likely(!klp_patch_pending(current)))
+		return;
+
+	/*
+	 * This function is called from cond_resched() which is called in many
+	 * places throughout the kernel.  Using the klp_mutex here might
+	 * deadlock.
+	 *
+	 * Instead, disable preemption to prevent racing with other callers of
+	 * klp_try_switch_task().  Thanks to task_call_func() they won't be
+	 * able to switch this task while it's running.
+	 */
+	preempt_disable();
+
+	/*
+	 * Make sure current didn't get patched between the above check and
+	 * preempt_disable().
+	 */
+	if (unlikely(!klp_patch_pending(current)))
+		goto out;
+
+	/*
+	 * Enforce the order of the TIF_PATCH_PENDING read above and the
+	 * klp_target_state read in klp_try_switch_task().  The corresponding
+	 * write barriers are in klp_init_transition() and
+	 * klp_reverse_transition().
+	 */
+	smp_rmb();
+
+	klp_try_switch_task(current);
+
+out:
+	preempt_enable();
+}
+EXPORT_SYMBOL(__klp_sched_try_switch);
+
+/*
+ * Sends a fake signal to all non-kthread tasks with TIF_PATCH_PENDING set.
+ * Kthreads with TIF_PATCH_PENDING set are woken up.
+ */
+static void klp_send_signals(void)
+{
+	struct task_struct *g, *task;
+
+	if (klp_signals_cnt == SIGNALS_TIMEOUT)
+		pr_notice("signaling remaining tasks\n");
+
+	read_lock(&tasklist_lock);
+	for_each_process_thread(g, task) {
+		if (!klp_patch_pending(task))
+			continue;
+
+		/*
+		 * There is a small race here. We could see TIF_PATCH_PENDING
+		 * set and decide to wake up a kthread or send a fake signal.
+		 * Meanwhile the task could migrate itself and the action
+		 * would be meaningless. It is not serious though.
+		 */
+		if (task->flags & PF_KTHREAD) {
+			/*
+			 * Wake up a kthread which sleeps interruptedly and
+			 * still has not been migrated.
+			 */
+			wake_up_state(task, TASK_INTERRUPTIBLE);
+		} else {
+			/*
+			 * Send fake signal to all non-kthread tasks which are
+			 * still not migrated.
+			 */
+			set_notify_signal(task);
+		}
+	}
+	read_unlock(&tasklist_lock);
+}
+
+/*
+ * Try to switch all remaining tasks to the target patch state by walking the
+ * stacks of sleeping tasks and looking for any to-be-patched or
+ * to-be-unpatched functions.  If such functions are found, the task can't be
+ * switched yet.
+ *
+ * If any tasks are still stuck in the initial patch state, schedule a retry.
+ */
+void klp_try_complete_transition(void)
+{
+	unsigned int cpu;
+	struct task_struct *g, *task;
+	struct klp_patch *patch;
+	bool complete = true;
+
+	WARN_ON_ONCE(klp_target_state == KLP_UNDEFINED);
+
+	/*
+	 * Try to switch the tasks to the target patch state by walking their
+	 * stacks and looking for any to-be-patched or to-be-unpatched
+	 * functions.  If such functions are found on a stack, or if the stack
+	 * is deemed unreliable, the task can't be switched yet.
+	 *
+	 * Usually this will transition most (or all) of the tasks on a system
+	 * unless the patch includes changes to a very common function.
+	 */
+	read_lock(&tasklist_lock);
+	for_each_process_thread(g, task)
+		if (!klp_try_switch_task(task))
+			complete = false;
+	read_unlock(&tasklist_lock);
+
+	/*
+	 * Ditto for the idle "swapper" tasks.
+	 */
+	cpus_read_lock();
+	for_each_possible_cpu(cpu) {
+		task = idle_task(cpu);
+		if (cpu_online(cpu)) {
+			if (!klp_try_switch_task(task)) {
+				complete = false;
+				/* Make idle task go through the main loop. */
+				wake_up_if_idle(cpu);
+			}
+		} else if (task->patch_state != klp_target_state) {
+			/* offline idle tasks can be switched immediately */
+			clear_tsk_thread_flag(task, TIF_PATCH_PENDING);
+			task->patch_state = klp_target_state;
+		}
+	}
+	cpus_read_unlock();
+
+	if (!complete) {
+		if (klp_signals_cnt && !(klp_signals_cnt % SIGNALS_TIMEOUT))
+			klp_send_signals();
+		klp_signals_cnt++;
+
+		/*
+		 * Some tasks weren't able to be switched over.  Try again
+		 * later and/or wait for other methods like kernel exit
+		 * switching.
+		 */
+		schedule_delayed_work(&klp_transition_work,
+				      round_jiffies_relative(HZ));
+		return;
+	}
+
+	/* Done!  Now cleanup the data structures. */
+	klp_cond_resched_disable();
+	patch = klp_transition_patch;
+	klp_complete_transition();
+
+	/*
+	 * It would make more sense to free the unused patches in
+	 * klp_complete_transition() but it is called also
+	 * from klp_cancel_transition().
+	 */
+	if (!patch->enabled)
+		klp_free_patch_async(patch);
+	else if (patch->replace)
+		klp_free_replaced_patches_async(patch);
+}
+
+/*
+ * Start the transition to the specified target patch state so tasks can begin
+ * switching to it.
+ */
+void klp_start_transition(void)
+{
+	struct task_struct *g, *task;
+	unsigned int cpu;
+
+	WARN_ON_ONCE(klp_target_state == KLP_UNDEFINED);
+
+	pr_notice("'%s': starting %s transition\n",
+		  klp_transition_patch->mod->name,
+		  klp_target_state == KLP_PATCHED ? "patching" : "unpatching");
+
+	/*
+	 * Mark all normal tasks as needing a patch state update.  They'll
+	 * switch either in klp_try_complete_transition() or as they exit the
+	 * kernel.
+	 */
+	read_lock(&tasklist_lock);
+	for_each_process_thread(g, task)
+		if (task->patch_state != klp_target_state)
+			set_tsk_thread_flag(task, TIF_PATCH_PENDING);
+	read_unlock(&tasklist_lock);
+
+	/*
+	 * Mark all idle tasks as needing a patch state update.  They'll switch
+	 * either in klp_try_complete_transition() or at the idle loop switch
+	 * point.
+	 */
+	for_each_possible_cpu(cpu) {
+		task = idle_task(cpu);
+		if (task->patch_state != klp_target_state)
+			set_tsk_thread_flag(task, TIF_PATCH_PENDING);
+	}
+
+	klp_cond_resched_enable();
+
+	klp_signals_cnt = 0;
+}
+
+/*
+ * Initialize the global target patch state and all tasks to the initial patch
+ * state, and initialize all function transition states to true in preparation
+ * for patching or unpatching.
+ */
+void klp_init_transition(struct klp_patch *patch, int state)
+{
+	struct task_struct *g, *task;
+	unsigned int cpu;
+	struct klp_object *obj;
+	struct klp_func *func;
+	int initial_state = !state;
+
+	WARN_ON_ONCE(klp_target_state != KLP_UNDEFINED);
+
+	klp_transition_patch = patch;
+
+	/*
+	 * Set the global target patch state which tasks will switch to.  This
+	 * has no effect until the TIF_PATCH_PENDING flags get set later.
+	 */
+	klp_target_state = state;
+
+	pr_debug("'%s': initializing %s transition\n", patch->mod->name,
+		 klp_target_state == KLP_PATCHED ? "patching" : "unpatching");
+
+	/*
+	 * Initialize all tasks to the initial patch state to prepare them for
+	 * switching to the target state.
+	 */
+	read_lock(&tasklist_lock);
+	for_each_process_thread(g, task) {
+		WARN_ON_ONCE(task->patch_state != KLP_UNDEFINED);
+		task->patch_state = initial_state;
+	}
+	read_unlock(&tasklist_lock);
+
+	/*
+	 * Ditto for the idle "swapper" tasks.
+	 */
+	for_each_possible_cpu(cpu) {
+		task = idle_task(cpu);
+		WARN_ON_ONCE(task->patch_state != KLP_UNDEFINED);
+		task->patch_state = initial_state;
+	}
+
+	/*
+	 * Enforce the order of the task->patch_state initializations and the
+	 * func->transition updates to ensure that klp_ftrace_handler() doesn't
+	 * see a func in transition with a task->patch_state of KLP_UNDEFINED.
+	 *
+	 * Also enforce the order of the klp_target_state write and future
+	 * TIF_PATCH_PENDING writes to ensure klp_update_patch_state() and
+	 * __klp_sched_try_switch() don't set a task->patch_state to
+	 * KLP_UNDEFINED.
+	 */
+	smp_wmb();
+
+	/*
+	 * Set the func transition states so klp_ftrace_handler() will know to
+	 * switch to the transition logic.
+	 *
+	 * When patching, the funcs aren't yet in the func_stack and will be
+	 * made visible to the ftrace handler shortly by the calls to
+	 * klp_patch_object().
+	 *
+	 * When unpatching, the funcs are already in the func_stack and so are
+	 * already visible to the ftrace handler.
+	 */
+	klp_for_each_object(patch, obj)
+		klp_for_each_func(obj, func)
+			func->transition = true;
+}
+
+/*
+ * This function can be called in the middle of an existing transition to
+ * reverse the direction of the target patch state.  This can be done to
+ * effectively cancel an existing enable or disable operation if there are any
+ * tasks which are stuck in the initial patch state.
+ */
+void klp_reverse_transition(void)
+{
+	unsigned int cpu;
+	struct task_struct *g, *task;
+
+	pr_debug("'%s': reversing transition from %s\n",
+		 klp_transition_patch->mod->name,
+		 klp_target_state == KLP_PATCHED ? "patching to unpatching" :
+						   "unpatching to patching");
+
+	/*
+	 * Clear all TIF_PATCH_PENDING flags to prevent races caused by
+	 * klp_update_patch_state() or __klp_sched_try_switch() running in
+	 * parallel with the reverse transition.
+	 */
+	read_lock(&tasklist_lock);
+	for_each_process_thread(g, task)
+		clear_tsk_thread_flag(task, TIF_PATCH_PENDING);
+	read_unlock(&tasklist_lock);
+
+	for_each_possible_cpu(cpu)
+		clear_tsk_thread_flag(idle_task(cpu), TIF_PATCH_PENDING);
+
+	/*
+	 * Make sure all existing invocations of klp_update_patch_state() and
+	 * __klp_sched_try_switch() see the cleared TIF_PATCH_PENDING before
+	 * starting the reverse transition.
+	 */
+	klp_synchronize_transition();
+
+	/*
+	 * All patching has stopped, now re-initialize the global variables to
+	 * prepare for the reverse transition.
+	 */
+	klp_transition_patch->enabled = !klp_transition_patch->enabled;
+	klp_target_state = !klp_target_state;
+
+	/*
+	 * Enforce the order of the klp_target_state write and the
+	 * TIF_PATCH_PENDING writes in klp_start_transition() to ensure
+	 * klp_update_patch_state() and __klp_sched_try_switch() don't set
+	 * task->patch_state to the wrong value.
+	 */
+	smp_wmb();
+
+	klp_start_transition();
+}
+
+/* Called from copy_process() during fork */
+void klp_copy_process(struct task_struct *child)
+{
+
+	/*
+	 * The parent process may have gone through a KLP transition since
+	 * the thread flag was copied in setup_thread_stack earlier. Bring
+	 * the task flag up to date with the parent here.
+	 *
+	 * The operation is serialized against all klp_*_transition()
+	 * operations by the tasklist_lock. The only exceptions are
+	 * klp_update_patch_state(current) and __klp_sched_try_switch(), but we
+	 * cannot race with them because we are current.
+	 */
+	if (test_tsk_thread_flag(current, TIF_PATCH_PENDING))
+		set_tsk_thread_flag(child, TIF_PATCH_PENDING);
+	else
+		clear_tsk_thread_flag(child, TIF_PATCH_PENDING);
+
+	child->patch_state = current->patch_state;
+}
+
+/*
+ * 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 klp_patch *patch;
+	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));
+
+	/* Set forced flag for patches being removed. */
+	if (klp_target_state == KLP_UNPATCHED)
+		klp_transition_patch->forced = true;
+	else if (klp_transition_patch->replace) {
+		klp_for_each_patch(patch) {
+			if (patch != klp_transition_patch)
+				patch->forced = true;
+		}
+	}
+}