Merge branches 'for-4.12/upstream' and 'for-4.12/klp-hybrid-consistency-model' into for-linus

7 files changed, 1043 insertions, 274 deletions

diff --git a/kernel/livepatch/Makefile b/kernel/livepatch/Makefile
index e8780c0901d9..2b8bdb1925da 100644
--- a/kernel/livepatch/Makefile
+++ b/kernel/livepatch/Makefile
@@ -1,3 +1,3 @@
 obj-$(CONFIG_LIVEPATCH) += livepatch.o
 
-livepatch-objs := core.o
+livepatch-objs := core.o patch.o transition.o
diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c
index 8739e9e0bdb8..b9628e43c78f 100644
--- a/kernel/livepatch/core.c
+++ b/kernel/livepatch/core.c
@@ -24,61 +24,31 @@
 #include <linux/kernel.h>
 #include <linux/mutex.h>
 #include <linux/slab.h>
-#include <linux/ftrace.h>
 #include <linux/list.h>
 #include <linux/kallsyms.h>
 #include <linux/livepatch.h>
 #include <linux/elf.h>
 #include <linux/moduleloader.h>
+#include <linux/completion.h>
 #include <asm/cacheflush.h>
-
-/**
- * struct klp_ops - structure for tracking registered ftrace ops structs
- *
- * A single ftrace_ops is shared between all enabled replacement functions
- * (klp_func structs) which have the same old_addr.  This allows the switch
- * between function versions to happen instantaneously by updating the klp_ops
- * struct's func_stack list.  The winner is the klp_func at the top of the
- * func_stack (front of the list).
- *
- * @node:       node for the global klp_ops list
- * @func_stack: list head for the stack of klp_func's (active func is on top)
- * @fops:       registered ftrace ops struct
- */
-struct klp_ops {
-        struct list_head node;
-        struct list_head func_stack;
-        struct ftrace_ops fops;
-};
+#include "core.h"
+#include "patch.h"
+#include "transition.h"
 
 /*
- * The klp_mutex protects the global lists and state transitions of any
- * structure reachable from them.  References to any structure must be obtained
- * under mutex protection (except in klp_ftrace_handler(), which uses RCU to
- * ensure it gets consistent data).
+ * klp_mutex is a coarse lock which serializes access to klp data.  All
+ * accesses to klp-related variables and structures must have mutex protection,
+ * except within the following functions which carefully avoid the need for it:
+ *
+ * - klp_ftrace_handler()
+ * - klp_update_patch_state()
  */
-static DEFINE_MUTEX(klp_mutex);
+DEFINE_MUTEX(klp_mutex);
 
 static LIST_HEAD(klp_patches);
-static LIST_HEAD(klp_ops);
 
 static struct kobject *klp_root_kobj;
 
-static struct klp_ops *klp_find_ops(unsigned long old_addr)
-{
-        struct klp_ops *ops;
-        struct klp_func *func;
-
-        list_for_each_entry(ops, &klp_ops, node) {
-                func = list_first_entry(&ops->func_stack, struct klp_func,
-                                        stack_node);
-                if (func->old_addr == old_addr)
-                        return ops;
-        }
-
-        return NULL;
-}
-
 static bool klp_is_module(struct klp_object *obj)
 {
         return obj->name;
@@ -117,7 +87,6 @@ static void klp_find_object_module(struct klp_object *obj)
         mutex_unlock(&module_mutex);
 }
 
-/* klp_mutex must be held by caller */
 static bool klp_is_patch_registered(struct klp_patch *patch)
 {
         struct klp_patch *mypatch;
@@ -314,191 +283,30 @@ static int klp_write_object_relocations(struct module *pmod,
         return ret;
 }
 
-static void notrace klp_ftrace_handler(unsigned long ip,
-                                       unsigned long parent_ip,
-                                       struct ftrace_ops *fops,
-                                       struct pt_regs *regs)
-{
-        struct klp_ops *ops;
-        struct klp_func *func;
-
-        ops = container_of(fops, struct klp_ops, fops);
-
-        rcu_read_lock();
-        func = list_first_or_null_rcu(&ops->func_stack, struct klp_func,
-                                      stack_node);
-        if (WARN_ON_ONCE(!func))
-                goto unlock;
-
-        klp_arch_set_pc(regs, (unsigned long)func->new_func);
-unlock:
-        rcu_read_unlock();
-}
-
-/*
- * Convert a function address into the appropriate ftrace location.
- *
- * Usually this is just the address of the function, but on some architectures
- * it's more complicated so allow them to provide a custom behaviour.
- */
-#ifndef klp_get_ftrace_location
-static unsigned long klp_get_ftrace_location(unsigned long faddr)
-{
-        return faddr;
-}
-#endif
-
-static void klp_disable_func(struct klp_func *func)
-{
-        struct klp_ops *ops;
-
-        if (WARN_ON(func->state != KLP_ENABLED))
-                return;
-        if (WARN_ON(!func->old_addr))
-                return;
-
-        ops = klp_find_ops(func->old_addr);
-        if (WARN_ON(!ops))
-                return;
-
-        if (list_is_singular(&ops->func_stack)) {
-                unsigned long ftrace_loc;
-
-                ftrace_loc = klp_get_ftrace_location(func->old_addr);
-                if (WARN_ON(!ftrace_loc))
-                        return;
-
-                WARN_ON(unregister_ftrace_function(&ops->fops));
-                WARN_ON(ftrace_set_filter_ip(&ops->fops, ftrace_loc, 1, 0));
-
-                list_del_rcu(&func->stack_node);
-                list_del(&ops->node);
-                kfree(ops);
-        } else {
-                list_del_rcu(&func->stack_node);
-        }
-
-        func->state = KLP_DISABLED;
-}
-
-static int klp_enable_func(struct klp_func *func)
-{
-        struct klp_ops *ops;
-        int ret;
-
-        if (WARN_ON(!func->old_addr))
-                return -EINVAL;
-
-        if (WARN_ON(func->state != KLP_DISABLED))
-                return -EINVAL;
-
-        ops = klp_find_ops(func->old_addr);
-        if (!ops) {
-                unsigned long ftrace_loc;
-
-                ftrace_loc = klp_get_ftrace_location(func->old_addr);
-                if (!ftrace_loc) {
-                        pr_err("failed to find location for function '%s'\n",
-                                func->old_name);
-                        return -EINVAL;
-                }
-
-                ops = kzalloc(sizeof(*ops), GFP_KERNEL);
-                if (!ops)
-                        return -ENOMEM;
-
-                ops->fops.func = klp_ftrace_handler;
-                ops->fops.flags = FTRACE_OPS_FL_SAVE_REGS |
-                                  FTRACE_OPS_FL_DYNAMIC |
-                                  FTRACE_OPS_FL_IPMODIFY;
-
-                list_add(&ops->node, &klp_ops);
-
-                INIT_LIST_HEAD(&ops->func_stack);
-                list_add_rcu(&func->stack_node, &ops->func_stack);
-
-                ret = ftrace_set_filter_ip(&ops->fops, ftrace_loc, 0, 0);
-                if (ret) {
-                        pr_err("failed to set ftrace filter for function '%s' (%d)\n",
-                               func->old_name, ret);
-                        goto err;
-                }
-
-                ret = register_ftrace_function(&ops->fops);
-                if (ret) {
-                        pr_err("failed to register ftrace handler for function '%s' (%d)\n",
-                               func->old_name, ret);
-                        ftrace_set_filter_ip(&ops->fops, ftrace_loc, 1, 0);
-                        goto err;
-                }
-
-
-        } else {
-                list_add_rcu(&func->stack_node, &ops->func_stack);
-        }
-
-        func->state = KLP_ENABLED;
-
-        return 0;
-
-err:
-        list_del_rcu(&func->stack_node);
-        list_del(&ops->node);
-        kfree(ops);
-        return ret;
-}
-
-static void klp_disable_object(struct klp_object *obj)
-{
-        struct klp_func *func;
-
-        klp_for_each_func(obj, func)
-                if (func->state == KLP_ENABLED)
-                        klp_disable_func(func);
-
-        obj->state = KLP_DISABLED;
-}
-
-static int klp_enable_object(struct klp_object *obj)
-{
-        struct klp_func *func;
-        int ret;
-
-        if (WARN_ON(obj->state != KLP_DISABLED))
-                return -EINVAL;
-
-        if (WARN_ON(!klp_is_object_loaded(obj)))
-                return -EINVAL;
-
-        klp_for_each_func(obj, func) {
-                ret = klp_enable_func(func);
-                if (ret) {
-                        klp_disable_object(obj);
-                        return ret;
-                }
-        }
-        obj->state = KLP_ENABLED;
-
-        return 0;
-}
-
 static int __klp_disable_patch(struct klp_patch *patch)
 {
-        struct klp_object *obj;
+        if (klp_transition_patch)
+                return -EBUSY;
 
         /* enforce stacking: only the last enabled patch can be disabled */
         if (!list_is_last(&patch->list, &klp_patches) &&
-            list_next_entry(patch, list)->state == KLP_ENABLED)
+            list_next_entry(patch, list)->enabled)
                 return -EBUSY;
 
-        pr_notice("disabling patch '%s'\n", patch->mod->name);
+        klp_init_transition(patch, KLP_UNPATCHED);
 
-        klp_for_each_object(patch, obj) {
-                if (obj->state == KLP_ENABLED)
-                        klp_disable_object(obj);
-        }
+        /*
+         * Enforce the order of the func->transition writes in
+         * klp_init_transition() and the TIF_PATCH_PENDING writes in
+         * klp_start_transition().  In the rare case where klp_ftrace_handler()
+         * is called shortly after klp_update_patch_state() switches the task,
+         * this ensures the handler sees that func->transition is set.
+         */
+        smp_wmb();
 
-        patch->state = KLP_DISABLED;
+        klp_start_transition();
+        klp_try_complete_transition();
+        patch->enabled = false;
 
         return 0;
 }
@@ -522,7 +330,7 @@ int klp_disable_patch(struct klp_patch *patch)
                 goto err;
         }
 
-        if (patch->state == KLP_DISABLED) {
+        if (!patch->enabled) {
                 ret = -EINVAL;
                 goto err;
         }
@@ -540,32 +348,61 @@ static int __klp_enable_patch(struct klp_patch *patch)
         struct klp_object *obj;
         int ret;
 
-        if (WARN_ON(patch->state != KLP_DISABLED))
+        if (klp_transition_patch)
+                return -EBUSY;
+
+        if (WARN_ON(patch->enabled))
                 return -EINVAL;
 
         /* enforce stacking: only the first disabled patch can be enabled */
         if (patch->list.prev != &klp_patches &&
-            list_prev_entry(patch, list)->state == KLP_DISABLED)
+            !list_prev_entry(patch, list)->enabled)
                 return -EBUSY;
 
+        /*
+         * A reference is taken on the patch module to prevent it from being
+         * unloaded.
+         *
+         * Note: For immediate (no consistency model) patches we don't allow
+         * patch modules to unload since there is no safe/sane method to
+         * determine if a thread is still running in the patched code contained
+         * in the patch module once the ftrace registration is successful.
+         */
+        if (!try_module_get(patch->mod))
+                return -ENODEV;
+
         pr_notice("enabling patch '%s'\n", patch->mod->name);
 
+        klp_init_transition(patch, KLP_PATCHED);
+
+        /*
+         * Enforce the order of the func->transition writes in
+         * klp_init_transition() and the ops->func_stack writes in
+         * klp_patch_object(), so that klp_ftrace_handler() will see the
+         * func->transition updates before the handler is registered and the
+         * new funcs become visible to the handler.
+         */
+        smp_wmb();
+
         klp_for_each_object(patch, obj) {
                 if (!klp_is_object_loaded(obj))
                         continue;
 
-                ret = klp_enable_object(obj);
-                if (ret)
-                        goto unregister;
+                ret = klp_patch_object(obj);
+                if (ret) {
+                        pr_warn("failed to enable patch '%s'\n",
+                                patch->mod->name);
+
+                        klp_cancel_transition();
+                        return ret;
+                }
         }
 
-        patch->state = KLP_ENABLED;
+        klp_start_transition();
+        klp_try_complete_transition();
+        patch->enabled = true;
 
         return 0;
-
-unregister:
-        WARN_ON(__klp_disable_patch(patch));
-        return ret;
 }
 
 /**
@@ -602,6 +439,7 @@ EXPORT_SYMBOL_GPL(klp_enable_patch);
  * /sys/kernel/livepatch
  * /sys/kernel/livepatch/<patch>
  * /sys/kernel/livepatch/<patch>/enabled
+ * /sys/kernel/livepatch/<patch>/transition
  * /sys/kernel/livepatch/<patch>/<object>
  * /sys/kernel/livepatch/<patch>/<object>/<function,sympos>
  */
@@ -611,26 +449,34 @@ static ssize_t enabled_store(struct kobject *kobj, struct kobj_attribute *attr,
 {
         struct klp_patch *patch;
         int ret;
-        unsigned long val;
+        bool enabled;
 
-        ret = kstrtoul(buf, 10, &val);
+        ret = kstrtobool(buf, &enabled);
         if (ret)
-                return -EINVAL;
-
-        if (val != KLP_DISABLED && val != KLP_ENABLED)
-                return -EINVAL;
+                return ret;
 
         patch = container_of(kobj, struct klp_patch, kobj);
 
         mutex_lock(&klp_mutex);
 
-        if (val == patch->state) {
+        if (!klp_is_patch_registered(patch)) {
+                /*
+                 * Module with the patch could either disappear meanwhile or is
+                 * not properly initialized yet.
+                 */
+                ret = -EINVAL;
+                goto err;
+        }
+
+        if (patch->enabled == enabled) {
                 /* already in requested state */
                 ret = -EINVAL;
                 goto err;
         }
 
-        if (val == KLP_ENABLED) {
+        if (patch == klp_transition_patch) {
+                klp_reverse_transition();
+        } else if (enabled) {
                 ret = __klp_enable_patch(patch);
                 if (ret)
                         goto err;
@@ -655,21 +501,33 @@ static ssize_t enabled_show(struct kobject *kobj,
         struct klp_patch *patch;
 
         patch = container_of(kobj, struct klp_patch, kobj);
-        return snprintf(buf, PAGE_SIZE-1, "%d\n", patch->state);
+        return snprintf(buf, PAGE_SIZE-1, "%d\n", patch->enabled);
+}
+
+static ssize_t transition_show(struct kobject *kobj,
+                               struct kobj_attribute *attr, char *buf)
+{
+        struct klp_patch *patch;
+
+        patch = container_of(kobj, struct klp_patch, kobj);
+        return snprintf(buf, PAGE_SIZE-1, "%d\n",
+                        patch == klp_transition_patch);
 }
 
 static struct kobj_attribute enabled_kobj_attr = __ATTR_RW(enabled);
+static struct kobj_attribute transition_kobj_attr = __ATTR_RO(transition);
 static struct attribute *klp_patch_attrs[] = {
         &enabled_kobj_attr.attr,
+        &transition_kobj_attr.attr,
         NULL
 };
 
 static void klp_kobj_release_patch(struct kobject *kobj)
 {
-        /*
-         * Once we have a consistency model we'll need to module_put() the
-         * patch module here.  See klp_register_patch() for more details.
-         */
+        struct klp_patch *patch;
+
+        patch = container_of(kobj, struct klp_patch, kobj);
+        complete(&patch->finish);
 }
 
 static struct kobj_type klp_ktype_patch = {
@@ -740,7 +598,6 @@ static void klp_free_patch(struct klp_patch *patch)
         klp_free_objects_limited(patch, NULL);
         if (!list_empty(&patch->list))
                 list_del(&patch->list);
-        kobject_put(&patch->kobj);
 }
 
 static int klp_init_func(struct klp_object *obj, struct klp_func *func)
@@ -749,7 +606,8 @@ static int klp_init_func(struct klp_object *obj, struct klp_func *func)
                 return -EINVAL;
 
         INIT_LIST_HEAD(&func->stack_node);
-        func->state = KLP_DISABLED;
+        func->patched = false;
+        func->transition = false;
 
         /* The format for the sysfs directory is <function,sympos> where sympos
          * is the nth occurrence of this symbol in kallsyms for the patched
@@ -790,6 +648,22 @@ static int klp_init_object_loaded(struct klp_patch *patch,
                                              &func->old_addr);
                 if (ret)
                         return ret;
+
+                ret = kallsyms_lookup_size_offset(func->old_addr,
+                                                  &func->old_size, NULL);
+                if (!ret) {
+                        pr_err("kallsyms size lookup failed for '%s'\n",
+                               func->old_name);
+                        return -ENOENT;
+                }
+
+                ret = kallsyms_lookup_size_offset((unsigned long)func->new_func,
+                                                  &func->new_size, NULL);
+                if (!ret) {
+                        pr_err("kallsyms size lookup failed for '%s' replacement\n",
+                               func->old_name);
+                        return -ENOENT;
+                }
         }
 
         return 0;
@@ -804,7 +678,7 @@ static int klp_init_object(struct klp_patch *patch, struct klp_object *obj)
         if (!obj->funcs)
                 return -EINVAL;
 
-        obj->state = KLP_DISABLED;
+        obj->patched = false;
         obj->mod = NULL;
 
         klp_find_object_module(obj);
@@ -845,12 +719,15 @@ static int klp_init_patch(struct klp_patch *patch)
 
         mutex_lock(&klp_mutex);
 
-        patch->state = KLP_DISABLED;
+        patch->enabled = false;
+        init_completion(&patch->finish);
 
         ret = kobject_init_and_add(&patch->kobj, &klp_ktype_patch,
                                    klp_root_kobj, "%s", patch->mod->name);
-        if (ret)
-                goto unlock;
+        if (ret) {
+                mutex_unlock(&klp_mutex);
+                return ret;
+        }
 
         klp_for_each_object(patch, obj) {
                 ret = klp_init_object(patch, obj);
@@ -866,9 +743,12 @@ static int klp_init_patch(struct klp_patch *patch)
 
 free:
         klp_free_objects_limited(patch, obj);
-        kobject_put(&patch->kobj);
-unlock:
+
         mutex_unlock(&klp_mutex);
+
+        kobject_put(&patch->kobj);
+        wait_for_completion(&patch->finish);
+
         return ret;
 }
 
@@ -882,23 +762,29 @@ unlock:
  */
 int klp_unregister_patch(struct klp_patch *patch)
 {
-        int ret = 0;
+        int ret;
 
         mutex_lock(&klp_mutex);
 
         if (!klp_is_patch_registered(patch)) {
                 ret = -EINVAL;
-                goto out;
+                goto err;
         }
 
-        if (patch->state == KLP_ENABLED) {
+        if (patch->enabled) {
                 ret = -EBUSY;
-                goto out;
+                goto err;
         }
 
         klp_free_patch(patch);
 
-out:
+        mutex_unlock(&klp_mutex);
+
+        kobject_put(&patch->kobj);
+        wait_for_completion(&patch->finish);
+
+        return 0;
+err:
         mutex_unlock(&klp_mutex);
         return ret;
 }
@@ -911,12 +797,13 @@ EXPORT_SYMBOL_GPL(klp_unregister_patch);
  * Initializes the data structure associated with the patch and
  * creates the sysfs interface.
  *
+ * There is no need to take the reference on the patch module here. It is done
+ * later when the patch is enabled.
+ *
  * Return: 0 on success, otherwise error
  */
 int klp_register_patch(struct klp_patch *patch)
 {
-        int ret;
-
         if (!patch || !patch->mod)
                 return -EINVAL;
 
@@ -930,20 +817,16 @@ int klp_register_patch(struct klp_patch *patch)
                 return -ENODEV;
 
         /*
-         * A reference is taken on the patch module to prevent it from being
-         * unloaded.  Right now, we don't allow patch modules to unload since
-         * there is currently no method to determine if a thread is still
-         * running in the patched code contained in the patch module once
-         * the ftrace registration is successful.
+         * Architectures without reliable stack traces have to set
+         * patch->immediate because there's currently no way to patch kthreads
+         * with the consistency model.
          */
-        if (!try_module_get(patch->mod))
-                return -ENODEV;
-
-        ret = klp_init_patch(patch);
-        if (ret)
-                module_put(patch->mod);
+        if (!klp_have_reliable_stack() && !patch->immediate) {
+                pr_err("This architecture doesn't have support for the livepatch consistency model.\n");
+                return -ENOSYS;
+        }
 
-        return ret;
+        return klp_init_patch(patch);
 }
 EXPORT_SYMBOL_GPL(klp_register_patch);
 
@@ -978,13 +861,17 @@ int klp_module_coming(struct module *mod)
                                 goto err;
                         }
 
-                        if (patch->state == KLP_DISABLED)
+                        /*
+                         * Only patch the module if the patch is enabled or is
+                         * in transition.
+                         */
+                        if (!patch->enabled && patch != klp_transition_patch)
                                 break;
 
                         pr_notice("applying patch '%s' to loading module '%s'\n",
                                   patch->mod->name, obj->mod->name);
 
-                        ret = klp_enable_object(obj);
+                        ret = klp_patch_object(obj);
                         if (ret) {
                                 pr_warn("failed to apply patch '%s' to module '%s' (%d)\n",
                                         patch->mod->name, obj->mod->name, ret);
@@ -1035,10 +922,14 @@ void klp_module_going(struct module *mod)
                         if (!klp_is_module(obj) || strcmp(obj->name, mod->name))
                                 continue;
 
-                        if (patch->state != KLP_DISABLED) {
+                        /*
+                         * Only unpatch the module if the patch is enabled or
+                         * is in transition.
+                         */
+                        if (patch->enabled || patch == klp_transition_patch) {
                                 pr_notice("reverting patch '%s' on unloading module '%s'\n",
                                           patch->mod->name, obj->mod->name);
-                                klp_disable_object(obj);
+                                klp_unpatch_object(obj);
                         }
 
                         klp_free_object_loaded(obj);
diff --git a/kernel/livepatch/core.h b/kernel/livepatch/core.h
new file mode 100644
index 000000000000..c74f24c47837
--- /dev/null
+++ b/kernel/livepatch/core.h
@@ -0,0 +1,6 @@
+#ifndef _LIVEPATCH_CORE_H
+#define _LIVEPATCH_CORE_H
+
+extern struct mutex klp_mutex;
+
+#endif /* _LIVEPATCH_CORE_H */
diff --git a/kernel/livepatch/patch.c b/kernel/livepatch/patch.c
new file mode 100644
index 000000000000..f8269036bf0b
--- /dev/null
+++ b/kernel/livepatch/patch.c
@@ -0,0 +1,272 @@
+/*
+ * patch.c - livepatch patching functions
+ *
+ * Copyright (C) 2014 Seth Jennings <sjenning@redhat.com>
+ * Copyright (C) 2014 SUSE
+ * Copyright (C) 2015 Josh Poimboeuf <jpoimboe@redhat.com>
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version 2
+ * of the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, see <http://www.gnu.org/licenses/>.
+ */
+
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include <linux/livepatch.h>
+#include <linux/list.h>
+#include <linux/ftrace.h>
+#include <linux/rculist.h>
+#include <linux/slab.h>
+#include <linux/bug.h>
+#include <linux/printk.h>
+#include "patch.h"
+#include "transition.h"
+
+static LIST_HEAD(klp_ops);
+
+struct klp_ops *klp_find_ops(unsigned long old_addr)
+{
+        struct klp_ops *ops;
+        struct klp_func *func;
+
+        list_for_each_entry(ops, &klp_ops, node) {
+                func = list_first_entry(&ops->func_stack, struct klp_func,
+                                        stack_node);
+                if (func->old_addr == old_addr)
+                        return ops;
+        }
+
+        return NULL;
+}
+
+static void notrace klp_ftrace_handler(unsigned long ip,
+                                       unsigned long parent_ip,
+                                       struct ftrace_ops *fops,
+                                       struct pt_regs *regs)
+{
+        struct klp_ops *ops;
+        struct klp_func *func;
+        int patch_state;
+
+        ops = container_of(fops, struct klp_ops, fops);
+
+        rcu_read_lock();
+
+        func = list_first_or_null_rcu(&ops->func_stack, struct klp_func,
+                                      stack_node);
+
+        /*
+         * func should never be NULL because preemption should be disabled here
+         * and unregister_ftrace_function() does the equivalent of a
+         * synchronize_sched() before the func_stack removal.
+         */
+        if (WARN_ON_ONCE(!func))
+                goto unlock;
+
+        /*
+         * In the enable path, enforce the order of the ops->func_stack and
+         * func->transition reads.  The corresponding write barrier is in
+         * __klp_enable_patch().
+         *
+         * (Note that this barrier technically isn't needed in the disable
+         * path.  In the rare case where klp_update_patch_state() runs before
+         * this handler, its TIF_PATCH_PENDING read and this func->transition
+         * read need to be ordered.  But klp_update_patch_state() already
+         * enforces that.)
+         */
+        smp_rmb();
+
+        if (unlikely(func->transition)) {
+
+                /*
+                 * Enforce the order of the func->transition and
+                 * current->patch_state reads.  Otherwise we could read an
+                 * out-of-date task state and pick the wrong function.  The
+                 * corresponding write barrier is in klp_init_transition().
+                 */
+                smp_rmb();
+
+                patch_state = current->patch_state;
+
+                WARN_ON_ONCE(patch_state == KLP_UNDEFINED);
+
+                if (patch_state == KLP_UNPATCHED) {
+                        /*
+                         * Use the previously patched version of the function.
+                         * If no previous patches exist, continue with the
+                         * original function.
+                         */
+                        func = list_entry_rcu(func->stack_node.next,
+                                              struct klp_func, stack_node);
+
+                        if (&func->stack_node == &ops->func_stack)
+                                goto unlock;
+                }
+        }
+
+        klp_arch_set_pc(regs, (unsigned long)func->new_func);
+unlock:
+        rcu_read_unlock();
+}
+
+/*
+ * Convert a function address into the appropriate ftrace location.
+ *
+ * Usually this is just the address of the function, but on some architectures
+ * it's more complicated so allow them to provide a custom behaviour.
+ */
+#ifndef klp_get_ftrace_location
+static unsigned long klp_get_ftrace_location(unsigned long faddr)
+{
+        return faddr;
+}
+#endif
+
+static void klp_unpatch_func(struct klp_func *func)
+{
+        struct klp_ops *ops;
+
+        if (WARN_ON(!func->patched))
+                return;
+        if (WARN_ON(!func->old_addr))
+                return;
+
+        ops = klp_find_ops(func->old_addr);
+        if (WARN_ON(!ops))
+                return;
+
+        if (list_is_singular(&ops->func_stack)) {
+                unsigned long ftrace_loc;
+
+                ftrace_loc = klp_get_ftrace_location(func->old_addr);
+                if (WARN_ON(!ftrace_loc))
+                        return;
+
+                WARN_ON(unregister_ftrace_function(&ops->fops));
+                WARN_ON(ftrace_set_filter_ip(&ops->fops, ftrace_loc, 1, 0));
+
+                list_del_rcu(&func->stack_node);
+                list_del(&ops->node);
+                kfree(ops);
+        } else {
+                list_del_rcu(&func->stack_node);
+        }
+
+        func->patched = false;
+}
+
+static int klp_patch_func(struct klp_func *func)
+{
+        struct klp_ops *ops;
+        int ret;
+
+        if (WARN_ON(!func->old_addr))
+                return -EINVAL;
+
+        if (WARN_ON(func->patched))
+                return -EINVAL;
+
+        ops = klp_find_ops(func->old_addr);
+        if (!ops) {
+                unsigned long ftrace_loc;
+
+                ftrace_loc = klp_get_ftrace_location(func->old_addr);
+                if (!ftrace_loc) {
+                        pr_err("failed to find location for function '%s'\n",
+                                func->old_name);
+                        return -EINVAL;
+                }
+
+                ops = kzalloc(sizeof(*ops), GFP_KERNEL);
+                if (!ops)
+                        return -ENOMEM;
+
+                ops->fops.func = klp_ftrace_handler;
+                ops->fops.flags = FTRACE_OPS_FL_SAVE_REGS |
+                                  FTRACE_OPS_FL_DYNAMIC |
+                                  FTRACE_OPS_FL_IPMODIFY;
+
+                list_add(&ops->node, &klp_ops);
+
+                INIT_LIST_HEAD(&ops->func_stack);
+                list_add_rcu(&func->stack_node, &ops->func_stack);
+
+                ret = ftrace_set_filter_ip(&ops->fops, ftrace_loc, 0, 0);
+                if (ret) {
+                        pr_err("failed to set ftrace filter for function '%s' (%d)\n",
+                               func->old_name, ret);
+                        goto err;
+                }
+
+                ret = register_ftrace_function(&ops->fops);
+                if (ret) {
+                        pr_err("failed to register ftrace handler for function '%s' (%d)\n",
+                               func->old_name, ret);
+                        ftrace_set_filter_ip(&ops->fops, ftrace_loc, 1, 0);
+                        goto err;
+                }
+
+
+        } else {
+                list_add_rcu(&func->stack_node, &ops->func_stack);
+        }
+
+        func->patched = true;
+
+        return 0;
+
+err:
+        list_del_rcu(&func->stack_node);
+        list_del(&ops->node);
+        kfree(ops);
+        return ret;
+}
+
+void klp_unpatch_object(struct klp_object *obj)
+{
+        struct klp_func *func;
+
+        klp_for_each_func(obj, func)
+                if (func->patched)
+                        klp_unpatch_func(func);
+
+        obj->patched = false;
+}
+
+int klp_patch_object(struct klp_object *obj)
+{
+        struct klp_func *func;
+        int ret;
+
+        if (WARN_ON(obj->patched))
+                return -EINVAL;
+
+        klp_for_each_func(obj, func) {
+                ret = klp_patch_func(func);
+                if (ret) {
+                        klp_unpatch_object(obj);
+                        return ret;
+                }
+        }
+        obj->patched = true;
+
+        return 0;
+}
+
+void klp_unpatch_objects(struct klp_patch *patch)
+{
+        struct klp_object *obj;
+
+        klp_for_each_object(patch, obj)
+                if (obj->patched)
+                        klp_unpatch_object(obj);
+}
diff --git a/kernel/livepatch/patch.h b/kernel/livepatch/patch.h
new file mode 100644
index 000000000000..0db227170c36
--- /dev/null
+++ b/kernel/livepatch/patch.h
@@ -0,0 +1,33 @@
+#ifndef _LIVEPATCH_PATCH_H
+#define _LIVEPATCH_PATCH_H
+
+#include <linux/livepatch.h>
+#include <linux/list.h>
+#include <linux/ftrace.h>
+
+/**
+ * struct klp_ops - structure for tracking registered ftrace ops structs
+ *
+ * A single ftrace_ops is shared between all enabled replacement functions
+ * (klp_func structs) which have the same old_addr.  This allows the switch
+ * between function versions to happen instantaneously by updating the klp_ops
+ * struct's func_stack list.  The winner is the klp_func at the top of the
+ * func_stack (front of the list).
+ *
+ * @node:       node for the global klp_ops list
+ * @func_stack: list head for the stack of klp_func's (active func is on top)
+ * @fops:       registered ftrace ops struct
+ */
+struct klp_ops {
+        struct list_head node;
+        struct list_head func_stack;
+        struct ftrace_ops fops;
+};
+
+struct klp_ops *klp_find_ops(unsigned long old_addr);
+
+int klp_patch_object(struct klp_object *obj);
+void klp_unpatch_object(struct klp_object *obj);
+void klp_unpatch_objects(struct klp_patch *patch);
+
+#endif /* _LIVEPATCH_PATCH_H */
diff --git a/kernel/livepatch/transition.c b/kernel/livepatch/transition.c
new file mode 100644
index 000000000000..adc0cc64aa4b
--- /dev/null
+++ b/kernel/livepatch/transition.c
@@ -0,0 +1,553 @@
+/*
+ * transition.c - Kernel Live Patching transition functions
+ *
+ * Copyright (C) 2015-2016 Josh Poimboeuf <jpoimboe@redhat.com>
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version 2
+ * of the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, see <http://www.gnu.org/licenses/>.
+ */
+
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include <linux/cpu.h>
+#include <linux/stacktrace.h>
+#include "core.h"
+#include "patch.h"
+#include "transition.h"
+#include "../sched/sched.h"
+
+#define MAX_STACK_ENTRIES  100
+#define STACK_ERR_BUF_SIZE 128
+
+struct klp_patch *klp_transition_patch;
+
+static int klp_target_state = KLP_UNDEFINED;
+
+/*
+ * 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);
+
+/*
+ * 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;
+        bool immediate_func = false;
+
+        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.
+                 */
+                synchronize_rcu();
+        }
+
+        if (klp_transition_patch->immediate)
+                goto done;
+
+        klp_for_each_object(klp_transition_patch, obj) {
+                klp_for_each_func(obj, func) {
+                        func->transition = false;
+                        if (func->immediate)
+                                immediate_func = true;
+                }
+        }
+
+        if (klp_target_state == KLP_UNPATCHED && !immediate_func)
+                module_put(klp_transition_patch->mod);
+
+        /* Prevent klp_ftrace_handler() from seeing KLP_UNDEFINED state */
+        if (klp_target_state == KLP_PATCHED)
+                synchronize_rcu();
+
+        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;
+        }
+
+done:
+        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;
+
+        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)
+{
+        rcu_read_lock();
+
+        /*
+         * 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 barrier is in
+         *    klp_init_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);
+
+        rcu_read_unlock();
+}
+
+/*
+ * 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,
+                                struct stack_trace *trace)
+{
+        unsigned long func_addr, func_size, address;
+        struct klp_ops *ops;
+        int i;
+
+        if (func->immediate)
+                return 0;
+
+        for (i = 0; i < trace->nr_entries; i++) {
+                address = trace->entries[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_addr);
+
+                        if (list_is_singular(&ops->func_stack)) {
+                                /* original function */
+                                func_addr = func->old_addr;
+                                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;
+                        }
+                }
+
+                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, char *err_buf)
+{
+        static unsigned long entries[MAX_STACK_ENTRIES];
+        struct stack_trace trace;
+        struct klp_object *obj;
+        struct klp_func *func;
+        int ret;
+
+        trace.skip = 0;
+        trace.nr_entries = 0;
+        trace.max_entries = MAX_STACK_ENTRIES;
+        trace.entries = entries;
+        ret = save_stack_trace_tsk_reliable(task, &trace);
+        WARN_ON_ONCE(ret == -ENOSYS);
+        if (ret) {
+                snprintf(err_buf, STACK_ERR_BUF_SIZE,
+                         "%s: %s:%d has an unreliable stack\n",
+                         __func__, task->comm, task->pid);
+                return 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, &trace);
+                        if (ret) {
+                                snprintf(err_buf, STACK_ERR_BUF_SIZE,
+                                         "%s: %s:%d is sleeping on function %s\n",
+                                         __func__, task->comm, task->pid,
+                                         func->old_name);
+                                return ret;
+                        }
+                }
+        }
+
+        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)
+{
+        struct rq *rq;
+        struct rq_flags flags;
+        int ret;
+        bool success = false;
+        char err_buf[STACK_ERR_BUF_SIZE];
+
+        err_buf[0] = '\0';
+
+        /* 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.
+         */
+        rq = task_rq_lock(task, &flags);
+
+        if (task_running(rq, task) && task != current) {
+                snprintf(err_buf, STACK_ERR_BUF_SIZE,
+                         "%s: %s:%d is running\n", __func__, task->comm,
+                         task->pid);
+                goto done;
+        }
+
+        ret = klp_check_stack(task, err_buf);
+        if (ret)
+                goto done;
+
+        success = true;
+
+        clear_tsk_thread_flag(task, TIF_PATCH_PENDING);
+        task->patch_state = klp_target_state;
+
+done:
+        task_rq_unlock(rq, task, &flags);
+
+        /*
+         * Due to console deadlock issues, pr_debug() can't be used while
+         * holding the task rq lock.  Instead we have to use a temporary buffer
+         * and print the debug message after releasing the lock.
+         */
+        if (err_buf[0] != '\0')
+                pr_debug("%s", err_buf);
+
+        return success;
+
+}
+
+/*
+ * 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;
+        bool complete = true;
+
+        WARN_ON_ONCE(klp_target_state == KLP_UNDEFINED);
+
+        /*
+         * If the patch can be applied or reverted immediately, skip the
+         * per-task transitions.
+         */
+        if (klp_transition_patch->immediate)
+                goto success;
+
+        /*
+         * 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.
+         */
+        get_online_cpus();
+        for_each_possible_cpu(cpu) {
+                task = idle_task(cpu);
+                if (cpu_online(cpu)) {
+                        if (!klp_try_switch_task(task))
+                                complete = false;
+                } 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;
+                }
+        }
+        put_online_cpus();
+
+        if (!complete) {
+                /*
+                 * 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;
+        }
+
+success:
+        pr_notice("'%s': %s complete\n", klp_transition_patch->mod->name,
+                  klp_target_state == KLP_PATCHED ? "patching" : "unpatching");
+
+        /* we're done, now cleanup the data structures */
+        klp_complete_transition();
+}
+
+/*
+ * 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': %s...\n", klp_transition_patch->mod->name,
+                  klp_target_state == KLP_PATCHED ? "patching" : "unpatching");
+
+        /*
+         * If the patch can be applied or reverted immediately, skip the
+         * per-task transitions.
+         */
+        if (klp_transition_patch->immediate)
+                return;
+
+        /*
+         * 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);
+        }
+}
+
+/*
+ * 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;
+
+        /*
+         * If the patch can be applied or reverted immediately, skip the
+         * per-task transitions.
+         */
+        if (patch->immediate)
+                return;
+
+        /*
+         * 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() doesn'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;
+
+        klp_transition_patch->enabled = !klp_transition_patch->enabled;
+
+        klp_target_state = !klp_target_state;
+
+        /*
+         * Clear all TIF_PATCH_PENDING flags to prevent races caused by
+         * klp_update_patch_state() running in parallel with
+         * klp_start_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);
+
+        /* Let any remaining calls to klp_update_patch_state() complete */
+        synchronize_rcu();
+
+        klp_start_transition();
+}
+
+/* Called from copy_process() during fork */
+void klp_copy_process(struct task_struct *child)
+{
+        child->patch_state = current->patch_state;
+
+        /* TIF_PATCH_PENDING gets copied in setup_thread_stack() */
+}
diff --git a/kernel/livepatch/transition.h b/kernel/livepatch/transition.h
new file mode 100644
index 000000000000..ce09b326546c
--- /dev/null
+++ b/kernel/livepatch/transition.h
@@ -0,0 +1,14 @@
+#ifndef _LIVEPATCH_TRANSITION_H
+#define _LIVEPATCH_TRANSITION_H
+
+#include <linux/livepatch.h>
+
+extern struct klp_patch *klp_transition_patch;
+
+void klp_init_transition(struct klp_patch *patch, int state);
+void klp_cancel_transition(void);
+void klp_start_transition(void);
+void klp_try_complete_transition(void);
+void klp_reverse_transition(void);
+
+#endif /* _LIVEPATCH_TRANSITION_H */