Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/jikos/livepatching

Pull livepatching updates from Jiri Kosina:

 - handle 'infinitely'-long sleeping tasks, from Miroslav Benes

 - remove 'immediate' feature, as it turns out it doesn't provide the
   originally expected semantics, and brings more issues than value

* 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/jikos/livepatching:
  livepatch: add locking to force and signal functions
  livepatch: Remove immediate feature
  livepatch: force transition to finish
  livepatch: send a fake signal to all blocking tasks

Documentation/ABI/testing/sysfs-kernel-livepatch

@@ -33,6 +33,32 @@ Description:
 		An attribute which indicates whether the patch is currently in
 		transition.
 
+What:		/sys/kernel/livepatch/<patch>/signal
+Date:		Nov 2017
+KernelVersion:	4.15.0
+Contact:	live-patching@vger.kernel.org
+Description:
+		A writable attribute that allows administrator to affect the
+		course of an existing transition. Writing 1 sends a fake
+		signal to all remaining blocking tasks. The fake signal
+		means that no proper signal is delivered (there is no data in
+		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@vger.kernel.org
+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. Removal (rmmod) of patch modules is permanently
+		disabled when the feature is used. See
+		Documentation/livepatch/livepatch.txt for more information.
+
 What:		/sys/kernel/livepatch/<patch>/<object>
 Date:		Nov 2014
 KernelVersion:	3.19.0

Documentation/livepatch/livepatch.txt

@@ -72,8 +72,7 @@ example, they add a NULL pointer or a boundary check, fix a race by adding
 a missing memory barrier, or add some locking around a critical section.
 Most of these changes are self contained and the function presents itself
 the same way to the rest of the system. In this case, the functions might
-be updated independently one by one.  (This can be done by setting the
+be updated independently one by one.
-'immediate' flag in the klp_patch struct.)
 
 But there are more complex fixes. For example, a patch might change
 ordering of locking in multiple functions at the same time. Or a patch
@@ -125,12 +124,6 @@ safe to patch tasks:
    b) Patching CPU-bound user tasks.  If the task is highly CPU-bound
       then it will get patched the next time it gets interrupted by an
       IRQ.
-   c) In the future it could be useful for applying patches for
-      architectures which don't yet have HAVE_RELIABLE_STACKTRACE.  In
-      this case you would have to signal most of the tasks on the
-      system.  However this isn't supported yet because there's
-      currently no way to patch kthreads without
-      HAVE_RELIABLE_STACKTRACE.
 
 3. For idle "swapper" tasks, since they don't ever exit the kernel, they
    instead have a klp_update_patch_state() call in the idle loop which
@@ -138,27 +131,16 @@ safe to patch tasks:
 
    (Note there's not yet such an approach for kthreads.)
 
-All the above approaches may be skipped by setting the 'immediate' flag
+Architectures which don't have HAVE_RELIABLE_STACKTRACE solely rely on
-in the 'klp_patch' struct, which will disable per-task consistency and
+the second approach. It's highly likely that some tasks may still be
-patch all tasks immediately.  This can be useful if the patch doesn't
+running with an old version of the function, until that function
-change any function or data semantics.  Note that, even with this flag
+returns. In this case you would have to signal the tasks. This
-set, it's possible that some tasks may still be running with an old
+especially applies to kthreads. They may not be woken up and would need
-version of the function, until that function returns.
+to be forced. See below for more information.
 
-There's also an 'immediate' flag in the 'klp_func' struct which allows
+Unless we can come up with another way to patch kthreads, architectures
-you to specify that certain functions in the patch can be applied
+without HAVE_RELIABLE_STACKTRACE are not considered fully supported by
-without per-task consistency.  This might be useful if you want to patch
+the kernel livepatching.
-a common function like schedule(), and the function change doesn't need
-consistency but the rest of the patch does.
-
-For architectures which don't have HAVE_RELIABLE_STACKTRACE, the user
-must set patch->immediate which causes all tasks to be patched
-immediately.  This option should be used with care, only when the patch
-doesn't change any function or data semantics.
-
-In the future, architectures which don't have HAVE_RELIABLE_STACKTRACE
-may be allowed to use per-task consistency if we can come up with
-another way to patch kthreads.
 
 The /sys/kernel/livepatch/<patch>/transition file shows whether a patch
 is in transition.  Only a single patch (the topmost patch on the stack)
@@ -176,8 +158,31 @@ If a patch is in transition, this file shows 0 to indicate the task is
 unpatched and 1 to indicate it's patched.  Otherwise, if no patch is in
 transition, it shows -1.  Any tasks which are blocking the transition
 can be signaled with SIGSTOP and SIGCONT to force them to change their
-patched state.
+patched state. This may be harmful to the system though.
+/sys/kernel/livepatch/<patch>/signal attribute provides a better alternative.
+Writing 1 to the attribute sends a fake signal to all remaining blocking
+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). Removal (rmmod) of patch
+modules is permanently disabled when the force feature is used. It cannot be
+guaranteed there is no task sleeping in such module. It implies unbounded
+reference count if a patch module is disabled and enabled in a loop.
+
+Moreover, the usage of force may also affect future applications of live
+patches and cause even more harm to the system. Administrator should first
+consider to simply cancel a transition (see above). If force is used, reboot
+should be planned and no more live patches applied.
 
 3.1 Adding consistency model support to new architectures
 ---------------------------------------------------------
@@ -216,13 +221,6 @@ few options:
    a good backup option for those architectures which don't have
    reliable stack traces yet.
 
-In the meantime, patches for such architectures can bypass the
-consistency model by setting klp_patch.immediate to true.  This option
-is perfectly fine for patches which don't change the semantics of the
-patched functions.  In practice, this is usable for ~90% of security
-fixes.  Use of this option also means the patch can't be unloaded after
-it has been disabled.
-
 
 4. Livepatch module
 ===================
@@ -278,9 +276,6 @@ into three levels:
     only for a particular object ( vmlinux or a kernel module ). Note that
     kallsyms allows for searching symbols according to the object name.
 
-    There's also an 'immediate' flag which, when set, patches the
-    function immediately, bypassing the consistency model safety checks.
-
   + struct klp_object defines an array of patched functions (struct
     klp_func) in the same object. Where the object is either vmlinux
     (NULL) or a module name.
@@ -299,9 +294,6 @@ into three levels:
     symbols are found. The only exception are symbols from objects
     (kernel modules) that have not been loaded yet.
 
-    Setting the 'immediate' flag applies the patch to all tasks
-    immediately, bypassing the consistency model safety checks.
-
     For more details on how the patch is applied on a per-task basis,
     see the "Consistency model" section.
 
@@ -316,14 +308,12 @@ section "Livepatch life-cycle" below for more details about these
 two operations.
 
 Module removal is only safe when there are no users of the underlying
-functions. The immediate consistency model is not able to detect this. The
+functions. This is the reason why the force feature permanently disables
-code just redirects the functions at the very beginning and it does not
+the removal. The forced tasks entered the functions but we cannot say
-check if the functions are in use. In other words, it knows when the
+that they returned back.  Therefore it cannot be decided when the
-functions get called but it does not know when the functions return.
+livepatch module can be safely removed. When the system is successfully
-Therefore it cannot be decided when the livepatch module can be safely
+transitioned to a new patch state (patched/unpatched) without being
-removed. This is solved by a hybrid consistency model. When the system is
+forced it is guaranteed that no task sleeps or runs in the old code.
-transitioned to a new patch state (patched/unpatched) it is guaranteed that
-no task sleeps or runs in the old code.
 
 
 5. Livepatch life-cycle
@@ -337,19 +327,12 @@ First, the patch is applied only when all patched symbols for already
 loaded objects are found. The error handling is much easier if this
 check is done before particular functions get redirected.
 
-Second, the immediate consistency model does not guarantee that anyone is not
+Second, it might take some time until the entire system is migrated with
-sleeping in the new code after the patch is reverted. This means that the new
+the hybrid consistency model being used. The patch revert might block
-code needs to stay around "forever". If the code is there, one could apply it
+the livepatch module removal for too long. Therefore it is useful to
-again. Therefore it makes sense to separate the operations that might be done
+revert the patch using a separate operation that might be called
-once and those that need to be repeated when the patch is enabled (applied)
+explicitly. But it does not make sense to remove all information until
-again.
+the livepatch module is really removed.
-
-Third, it might take some time until the entire system is migrated
-when a more complex consistency model is used. The patch revert might
-block the livepatch module removal for too long. Therefore it is useful
-to revert the patch using a separate operation that might be called
-explicitly. But it does not make sense to remove all information
-until the livepatch module is really removed.
 
 
 5.1. Registration
@@ -435,6 +418,9 @@ 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 and /sys/kernel/livepatch/<patch>/force
+attributes allow administrator to affect a patching operation.
+
 See Documentation/ABI/testing/sysfs-kernel-livepatch for more details.
 
 

arch/powerpc/kernel/signal.c

@@ -153,6 +153,9 @@ void do_notify_resume(struct pt_regs *regs, unsigned long thread_info_flags)
 	if (thread_info_flags & _TIF_UPROBE)
 		uprobe_notify_resume(regs);
 
+	if (thread_info_flags & _TIF_PATCH_PENDING)
+		klp_update_patch_state(current);
+
 	if (thread_info_flags & _TIF_SIGPENDING) {
 		BUG_ON(regs != current->thread.regs);
 		do_signal(current);
@@ -163,9 +166,6 @@ void do_notify_resume(struct pt_regs *regs, unsigned long thread_info_flags)
 		tracehook_notify_resume(regs);
 	}
 
-	if (thread_info_flags & _TIF_PATCH_PENDING)
-		klp_update_patch_state(current);
-
 	user_enter();
 }
 

arch/x86/entry/common.c

@@ -153,6 +153,9 @@ static void exit_to_usermode_loop(struct pt_regs *regs, u32 cached_flags)
 		if (cached_flags & _TIF_UPROBE)
 			uprobe_notify_resume(regs);
 
+		if (cached_flags & _TIF_PATCH_PENDING)
+			klp_update_patch_state(current);
+
 		/* deal with pending signal delivery */
 		if (cached_flags & _TIF_SIGPENDING)
 			do_signal(regs);
@@ -165,9 +168,6 @@ static void exit_to_usermode_loop(struct pt_regs *regs, u32 cached_flags)
 		if (cached_flags & _TIF_USER_RETURN_NOTIFY)
 			fire_user_return_notifiers();
 
-		if (cached_flags & _TIF_PATCH_PENDING)
-			klp_update_patch_state(current);
-
 		/* Disable IRQs and retry */
 		local_irq_disable();
 

include/linux/livepatch.h

@@ -40,7 +40,6 @@
  * @new_func:	pointer to the patched function code
  * @old_sympos: a hint indicating which symbol position the old function
  *		can be found (optional)
- * @immediate:  patch the func immediately, bypassing safety mechanisms
  * @old_addr:	the address of the function being patched
  * @kobj:	kobject for sysfs resources
  * @stack_node:	list node for klp_ops func_stack list
@@ -76,7 +75,6 @@ struct klp_func {
 	 * in kallsyms for the given object is used.
 	 */
 	unsigned long old_sympos;
-	bool immediate;
 
 	/* internal */
 	unsigned long old_addr;
@@ -137,7 +135,6 @@ struct klp_object {
  * struct klp_patch - patch structure for live patching
  * @mod:	reference to the live patch module
  * @objs:	object entries for kernel objects to be patched
- * @immediate:  patch all funcs immediately, bypassing safety mechanisms
  * @list:	list node for global list of registered patches
  * @kobj:	kobject for sysfs resources
  * @enabled:	the patch is enabled (but operation may be incomplete)
@@ -147,7 +144,6 @@ struct klp_patch {
 	/* external */
 	struct module *mod;
 	struct klp_object *objs;
-	bool immediate;
 
 	/* internal */
 	struct list_head list;

kernel/livepatch/core.c

@@ -366,11 +366,6 @@ static int __klp_enable_patch(struct klp_patch *patch)
 	/*
 	 * 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;
@@ -454,6 +449,8 @@ EXPORT_SYMBOL_GPL(klp_enable_patch);
  * /sys/kernel/livepatch/<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>
  */
@@ -528,11 +525,73 @@ static ssize_t transition_show(struct kobject *kobj,
 			patch == klp_transition_patch);
 }
 
+static ssize_t signal_store(struct kobject *kobj, struct kobj_attribute *attr,
+			    const char *buf, size_t count)
+{
+	struct klp_patch *patch;
+	int ret;
+	bool val;
+
+	ret = kstrtobool(buf, &val);
+	if (ret)
+		return ret;
+
+	if (!val)
+		return count;
+
+	mutex_lock(&klp_mutex);
+
+	patch = container_of(kobj, struct klp_patch, kobj);
+	if (patch != klp_transition_patch) {
+		mutex_unlock(&klp_mutex);
+		return -EINVAL;
+	}
+
+	klp_send_signals();
+
+	mutex_unlock(&klp_mutex);
+
+	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;
+
+	ret = kstrtobool(buf, &val);
+	if (ret)
+		return ret;
+
+	if (!val)
+		return count;
+
+	mutex_lock(&klp_mutex);
+
+	patch = container_of(kobj, struct klp_patch, kobj);
+	if (patch != klp_transition_patch) {
+		mutex_unlock(&klp_mutex);
+		return -EINVAL;
+	}
+
+	klp_force_transition();
+
+	mutex_unlock(&klp_mutex);
+
+	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
 };
 
@@ -830,12 +889,7 @@ int klp_register_patch(struct klp_patch *patch)
 	if (!klp_initialized())
 		return -ENODEV;
 
-	/*
+	if (!klp_have_reliable_stack()) {
-	 * Architectures without reliable stack traces have to set
-	 * patch->immediate because there's currently no way to patch kthreads
-	 * with the consistency model.
-	 */
-	if (!klp_have_reliable_stack() && !patch->immediate) {
 		pr_err("This architecture doesn't have support for the livepatch consistency model.\n");
 		return -ENOSYS;
 	}

kernel/livepatch/transition.c

@@ -33,6 +33,8 @@ 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.
@@ -80,7 +82,6 @@ static void klp_complete_transition(void)
 	struct klp_func *func;
 	struct task_struct *g, *task;
 	unsigned int cpu;
-	bool immediate_func = false;
 
 	pr_debug("'%s': completing %s transition\n",
 		 klp_transition_patch->mod->name,
@@ -102,16 +103,9 @@ static void klp_complete_transition(void)
 		klp_synchronize_transition();
 	}
 
-	if (klp_transition_patch->immediate)
+	klp_for_each_object(klp_transition_patch, obj)
-		goto done;
+		klp_for_each_func(obj, func)
-
-	klp_for_each_object(klp_transition_patch, obj) {
-		klp_for_each_func(obj, func) {
 			func->transition = false;
-			if (func->immediate)
-				immediate_func = true;
-		}
-	}
 
 	/* Prevent klp_ftrace_handler() from seeing KLP_UNDEFINED state */
 	if (klp_target_state == KLP_PATCHED)
@@ -130,7 +124,6 @@ static void klp_complete_transition(void)
 		task->patch_state = KLP_UNDEFINED;
 	}
 
-done:
 	klp_for_each_object(klp_transition_patch, obj) {
 		if (!klp_is_object_loaded(obj))
 			continue;
@@ -144,13 +137,11 @@ done:
 		  klp_target_state == KLP_PATCHED ? "patching" : "unpatching");
 
 	/*
-	 * See complementary comment in __klp_enable_patch() for why we
+	 * klp_forced set implies unbounded increase of module's ref count if
-	 * keep the module reference for immediate patches.
+	 * the module is disabled/enabled in a loop.
 	 */
-	if (!klp_transition_patch->immediate && !immediate_func &&
+	if (!klp_forced && klp_target_state == KLP_UNPATCHED)
-	    klp_target_state == KLP_UNPATCHED) {
 		module_put(klp_transition_patch->mod);
-	}
 
 	klp_target_state = KLP_UNDEFINED;
 	klp_transition_patch = NULL;
@@ -218,9 +209,6 @@ static int klp_check_stack_func(struct klp_func *func,
 	struct klp_ops *ops;
 	int i;
 
-	if (func->immediate)
-		return 0;
-
 	for (i = 0; i < trace->nr_entries; i++) {
 		address = trace->entries[i];
 
@@ -382,13 +370,6 @@ void klp_try_complete_transition(void)
 
 	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
@@ -432,7 +413,6 @@ void klp_try_complete_transition(void)
 		return;
 	}
 
-success:
 	/* we're done, now cleanup the data structures */
 	klp_complete_transition();
 }
@@ -452,13 +432,6 @@ void klp_start_transition(void)
 		  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
@@ -508,13 +481,6 @@ void klp_init_transition(struct klp_patch *patch, int state)
 	pr_debug("'%s': initializing %s transition\n", 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 (patch->immediate)
-		return;
-
 	/*
 	 * Initialize all tasks to the initial patch state to prepare them for
 	 * switching to the target state.
@@ -608,3 +574,71 @@ void klp_copy_process(struct task_struct *child)
 
 	/* TIF_PATCH_PENDING gets copied in setup_thread_stack() */
 }
+
+/*
+ * Sends a fake signal to all non-kthread tasks with TIF_PATCH_PENDING set.
+ * Kthreads with TIF_PATCH_PENDING set are woken up. Only admin can request this
+ * action currently.
+ */
+void klp_send_signals(void)
+{
+	struct task_struct *g, *task;
+
+	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.
+			 */
+			spin_lock_irq(&task->sighand->siglock);
+			signal_wake_up(task, 0);
+			spin_unlock_irq(&task->sighand->siglock);
+		}
+	}
+	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));
+
+	klp_forced = true;
+}

kernel/livepatch/transition.h

@@ -11,5 +11,7 @@ void klp_cancel_transition(void);
 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 */

kernel/signal.c

@@ -40,6 +40,7 @@
 #include <linux/cn_proc.h>
 #include <linux/compiler.h>
 #include <linux/posix-timers.h>
+#include <linux/livepatch.h>
 
 #define CREATE_TRACE_POINTS
 #include <trace/events/signal.h>
@@ -165,7 +166,8 @@ void recalc_sigpending_and_wake(struct task_struct *t)
 
 void recalc_sigpending(void)
 {
-	if (!recalc_sigpending_tsk(current) && !freezing(current))
+	if (!recalc_sigpending_tsk(current) && !freezing(current) &&
+	    !klp_patch_pending(current))
 		clear_thread_flag(TIF_SIGPENDING);
 
 }

samples/livepatch/livepatch-callbacks-demo.c

@@ -197,21 +197,6 @@ static int livepatch_callbacks_demo_init(void)
 {
 	int ret;
 
-	if (!klp_have_reliable_stack() && !patch.immediate) {
-		/*
-		 * WARNING: Be very careful when using 'patch.immediate' in
-		 * your patches.  It's ok to use it for simple patches like
-		 * this, but for more complex patches which change function
-		 * semantics, locking semantics, or data structures, it may not
-		 * be safe.  Use of this option will also prevent removal of
-		 * the patch.
-		 *
-		 * See Documentation/livepatch/livepatch.txt for more details.
-		 */
-		patch.immediate = true;
-		pr_notice("The consistency model isn't supported for your architecture.  Bypassing safety mechanisms and applying the patch immediately.\n");
-	}
-
 	ret = klp_register_patch(&patch);
 	if (ret)
 		return ret;

samples/livepatch/livepatch-sample.c

@@ -71,21 +71,6 @@ static int livepatch_init(void)
 {
 	int ret;
 
-	if (!klp_have_reliable_stack() && !patch.immediate) {
-		/*
-		 * WARNING: Be very careful when using 'patch.immediate' in
-		 * your patches.  It's ok to use it for simple patches like
-		 * this, but for more complex patches which change function
-		 * semantics, locking semantics, or data structures, it may not
-		 * be safe.  Use of this option will also prevent removal of
-		 * the patch.
-		 *
-		 * See Documentation/livepatch/livepatch.txt for more details.
-		 */
-		patch.immediate = true;
-		pr_notice("The consistency model isn't supported for your architecture.  Bypassing safety mechanisms and applying the patch immediately.\n");
-	}
-
 	ret = klp_register_patch(&patch);
 	if (ret)
 		return ret;

samples/livepatch/livepatch-shadow-fix1.c

@@ -133,21 +133,6 @@ static int livepatch_shadow_fix1_init(void)
 {
 	int ret;
 
-	if (!klp_have_reliable_stack() && !patch.immediate) {
-		/*
-		 * WARNING: Be very careful when using 'patch.immediate' in
-		 * your patches.  It's ok to use it for simple patches like
-		 * this, but for more complex patches which change function
-		 * semantics, locking semantics, or data structures, it may not
-		 * be safe.  Use of this option will also prevent removal of
-		 * the patch.
-		 *
-		 * See Documentation/livepatch/livepatch.txt for more details.
-		 */
-		patch.immediate = true;
-		pr_notice("The consistency model isn't supported for your architecture.  Bypassing safety mechanisms and applying the patch immediately.\n");
-	}
-
 	ret = klp_register_patch(&patch);
 	if (ret)
 		return ret;

samples/livepatch/livepatch-shadow-fix2.c

@@ -128,21 +128,6 @@ static int livepatch_shadow_fix2_init(void)
 {
 	int ret;
 
-	if (!klp_have_reliable_stack() && !patch.immediate) {
-		/*
-		 * WARNING: Be very careful when using 'patch.immediate' in
-		 * your patches.  It's ok to use it for simple patches like
-		 * this, but for more complex patches which change function
-		 * semantics, locking semantics, or data structures, it may not
-		 * be safe.  Use of this option will also prevent removal of
-		 * the patch.
-		 *
-		 * See Documentation/livepatch/livepatch.txt for more details.
-		 */
-		patch.immediate = true;
-		pr_notice("The consistency model isn't supported for your architecture.  Bypassing safety mechanisms and applying the patch immediately.\n");
-	}
-
 	ret = klp_register_patch(&patch);
 	if (ret)
 		return ret;