v4.19.13 snapshot.
diff --git a/kernel/stop_machine.c b/kernel/stop_machine.c
new file mode 100644
index 0000000..067cb83
--- /dev/null
+++ b/kernel/stop_machine.c
@@ -0,0 +1,682 @@
+/*
+ * kernel/stop_machine.c
+ *
+ * Copyright (C) 2008, 2005 IBM Corporation.
+ * Copyright (C) 2008, 2005 Rusty Russell rusty@rustcorp.com.au
+ * Copyright (C) 2010 SUSE Linux Products GmbH
+ * Copyright (C) 2010 Tejun Heo <tj@kernel.org>
+ *
+ * This file is released under the GPLv2 and any later version.
+ */
+#include <linux/completion.h>
+#include <linux/cpu.h>
+#include <linux/init.h>
+#include <linux/kthread.h>
+#include <linux/export.h>
+#include <linux/percpu.h>
+#include <linux/sched.h>
+#include <linux/stop_machine.h>
+#include <linux/interrupt.h>
+#include <linux/kallsyms.h>
+#include <linux/smpboot.h>
+#include <linux/atomic.h>
+#include <linux/nmi.h>
+#include <linux/sched/wake_q.h>
+
+/*
+ * Structure to determine completion condition and record errors. May
+ * be shared by works on different cpus.
+ */
+struct cpu_stop_done {
+ atomic_t nr_todo; /* nr left to execute */
+ int ret; /* collected return value */
+ struct completion completion; /* fired if nr_todo reaches 0 */
+};
+
+/* the actual stopper, one per every possible cpu, enabled on online cpus */
+struct cpu_stopper {
+ struct task_struct *thread;
+
+ raw_spinlock_t lock;
+ bool enabled; /* is this stopper enabled? */
+ struct list_head works; /* list of pending works */
+
+ struct cpu_stop_work stop_work; /* for stop_cpus */
+};
+
+static DEFINE_PER_CPU(struct cpu_stopper, cpu_stopper);
+static bool stop_machine_initialized = false;
+
+/* static data for stop_cpus */
+static DEFINE_MUTEX(stop_cpus_mutex);
+static bool stop_cpus_in_progress;
+
+static void cpu_stop_init_done(struct cpu_stop_done *done, unsigned int nr_todo)
+{
+ memset(done, 0, sizeof(*done));
+ atomic_set(&done->nr_todo, nr_todo);
+ init_completion(&done->completion);
+}
+
+/* signal completion unless @done is NULL */
+static void cpu_stop_signal_done(struct cpu_stop_done *done)
+{
+ if (atomic_dec_and_test(&done->nr_todo))
+ complete(&done->completion);
+}
+
+static void __cpu_stop_queue_work(struct cpu_stopper *stopper,
+ struct cpu_stop_work *work,
+ struct wake_q_head *wakeq)
+{
+ list_add_tail(&work->list, &stopper->works);
+ wake_q_add(wakeq, stopper->thread);
+}
+
+/* queue @work to @stopper. if offline, @work is completed immediately */
+static bool cpu_stop_queue_work(unsigned int cpu, struct cpu_stop_work *work)
+{
+ struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
+ DEFINE_WAKE_Q(wakeq);
+ unsigned long flags;
+ bool enabled;
+
+ preempt_disable();
+ raw_spin_lock_irqsave(&stopper->lock, flags);
+ enabled = stopper->enabled;
+ if (enabled)
+ __cpu_stop_queue_work(stopper, work, &wakeq);
+ else if (work->done)
+ cpu_stop_signal_done(work->done);
+ raw_spin_unlock_irqrestore(&stopper->lock, flags);
+
+ wake_up_q(&wakeq);
+ preempt_enable();
+
+ return enabled;
+}
+
+/**
+ * stop_one_cpu - stop a cpu
+ * @cpu: cpu to stop
+ * @fn: function to execute
+ * @arg: argument to @fn
+ *
+ * Execute @fn(@arg) on @cpu. @fn is run in a process context with
+ * the highest priority preempting any task on the cpu and
+ * monopolizing it. This function returns after the execution is
+ * complete.
+ *
+ * This function doesn't guarantee @cpu stays online till @fn
+ * completes. If @cpu goes down in the middle, execution may happen
+ * partially or fully on different cpus. @fn should either be ready
+ * for that or the caller should ensure that @cpu stays online until
+ * this function completes.
+ *
+ * CONTEXT:
+ * Might sleep.
+ *
+ * RETURNS:
+ * -ENOENT if @fn(@arg) was not executed because @cpu was offline;
+ * otherwise, the return value of @fn.
+ */
+int stop_one_cpu(unsigned int cpu, cpu_stop_fn_t fn, void *arg)
+{
+ struct cpu_stop_done done;
+ struct cpu_stop_work work = { .fn = fn, .arg = arg, .done = &done };
+
+ cpu_stop_init_done(&done, 1);
+ if (!cpu_stop_queue_work(cpu, &work))
+ return -ENOENT;
+ /*
+ * In case @cpu == smp_proccessor_id() we can avoid a sleep+wakeup
+ * cycle by doing a preemption:
+ */
+ cond_resched();
+ wait_for_completion(&done.completion);
+ return done.ret;
+}
+
+/* This controls the threads on each CPU. */
+enum multi_stop_state {
+ /* Dummy starting state for thread. */
+ MULTI_STOP_NONE,
+ /* Awaiting everyone to be scheduled. */
+ MULTI_STOP_PREPARE,
+ /* Disable interrupts. */
+ MULTI_STOP_DISABLE_IRQ,
+ /* Run the function */
+ MULTI_STOP_RUN,
+ /* Exit */
+ MULTI_STOP_EXIT,
+};
+
+struct multi_stop_data {
+ cpu_stop_fn_t fn;
+ void *data;
+ /* Like num_online_cpus(), but hotplug cpu uses us, so we need this. */
+ unsigned int num_threads;
+ const struct cpumask *active_cpus;
+
+ enum multi_stop_state state;
+ atomic_t thread_ack;
+};
+
+static void set_state(struct multi_stop_data *msdata,
+ enum multi_stop_state newstate)
+{
+ /* Reset ack counter. */
+ atomic_set(&msdata->thread_ack, msdata->num_threads);
+ smp_wmb();
+ msdata->state = newstate;
+}
+
+/* Last one to ack a state moves to the next state. */
+static void ack_state(struct multi_stop_data *msdata)
+{
+ if (atomic_dec_and_test(&msdata->thread_ack))
+ set_state(msdata, msdata->state + 1);
+}
+
+/* This is the cpu_stop function which stops the CPU. */
+static int multi_cpu_stop(void *data)
+{
+ struct multi_stop_data *msdata = data;
+ enum multi_stop_state curstate = MULTI_STOP_NONE;
+ int cpu = smp_processor_id(), err = 0;
+ unsigned long flags;
+ bool is_active;
+
+ /*
+ * When called from stop_machine_from_inactive_cpu(), irq might
+ * already be disabled. Save the state and restore it on exit.
+ */
+ local_save_flags(flags);
+
+ if (!msdata->active_cpus)
+ is_active = cpu == cpumask_first(cpu_online_mask);
+ else
+ is_active = cpumask_test_cpu(cpu, msdata->active_cpus);
+
+ /* Simple state machine */
+ do {
+ /* Chill out and ensure we re-read multi_stop_state. */
+ cpu_relax_yield();
+ if (msdata->state != curstate) {
+ curstate = msdata->state;
+ switch (curstate) {
+ case MULTI_STOP_DISABLE_IRQ:
+ local_irq_disable();
+ hard_irq_disable();
+ break;
+ case MULTI_STOP_RUN:
+ if (is_active)
+ err = msdata->fn(msdata->data);
+ break;
+ default:
+ break;
+ }
+ ack_state(msdata);
+ } else if (curstate > MULTI_STOP_PREPARE) {
+ /*
+ * At this stage all other CPUs we depend on must spin
+ * in the same loop. Any reason for hard-lockup should
+ * be detected and reported on their side.
+ */
+ touch_nmi_watchdog();
+ }
+ } while (curstate != MULTI_STOP_EXIT);
+
+ local_irq_restore(flags);
+ return err;
+}
+
+static int cpu_stop_queue_two_works(int cpu1, struct cpu_stop_work *work1,
+ int cpu2, struct cpu_stop_work *work2)
+{
+ struct cpu_stopper *stopper1 = per_cpu_ptr(&cpu_stopper, cpu1);
+ struct cpu_stopper *stopper2 = per_cpu_ptr(&cpu_stopper, cpu2);
+ DEFINE_WAKE_Q(wakeq);
+ int err;
+
+retry:
+ /*
+ * The waking up of stopper threads has to happen in the same
+ * scheduling context as the queueing. Otherwise, there is a
+ * possibility of one of the above stoppers being woken up by another
+ * CPU, and preempting us. This will cause us to not wake up the other
+ * stopper forever.
+ */
+ preempt_disable();
+ raw_spin_lock_irq(&stopper1->lock);
+ raw_spin_lock_nested(&stopper2->lock, SINGLE_DEPTH_NESTING);
+
+ if (!stopper1->enabled || !stopper2->enabled) {
+ err = -ENOENT;
+ goto unlock;
+ }
+
+ /*
+ * Ensure that if we race with __stop_cpus() the stoppers won't get
+ * queued up in reverse order leading to system deadlock.
+ *
+ * We can't miss stop_cpus_in_progress if queue_stop_cpus_work() has
+ * queued a work on cpu1 but not on cpu2, we hold both locks.
+ *
+ * It can be falsely true but it is safe to spin until it is cleared,
+ * queue_stop_cpus_work() does everything under preempt_disable().
+ */
+ if (unlikely(stop_cpus_in_progress)) {
+ err = -EDEADLK;
+ goto unlock;
+ }
+
+ err = 0;
+ __cpu_stop_queue_work(stopper1, work1, &wakeq);
+ __cpu_stop_queue_work(stopper2, work2, &wakeq);
+
+unlock:
+ raw_spin_unlock(&stopper2->lock);
+ raw_spin_unlock_irq(&stopper1->lock);
+
+ if (unlikely(err == -EDEADLK)) {
+ preempt_enable();
+
+ while (stop_cpus_in_progress)
+ cpu_relax();
+
+ goto retry;
+ }
+
+ wake_up_q(&wakeq);
+ preempt_enable();
+
+ return err;
+}
+/**
+ * stop_two_cpus - stops two cpus
+ * @cpu1: the cpu to stop
+ * @cpu2: the other cpu to stop
+ * @fn: function to execute
+ * @arg: argument to @fn
+ *
+ * Stops both the current and specified CPU and runs @fn on one of them.
+ *
+ * returns when both are completed.
+ */
+int stop_two_cpus(unsigned int cpu1, unsigned int cpu2, cpu_stop_fn_t fn, void *arg)
+{
+ struct cpu_stop_done done;
+ struct cpu_stop_work work1, work2;
+ struct multi_stop_data msdata;
+
+ msdata = (struct multi_stop_data){
+ .fn = fn,
+ .data = arg,
+ .num_threads = 2,
+ .active_cpus = cpumask_of(cpu1),
+ };
+
+ work1 = work2 = (struct cpu_stop_work){
+ .fn = multi_cpu_stop,
+ .arg = &msdata,
+ .done = &done
+ };
+
+ cpu_stop_init_done(&done, 2);
+ set_state(&msdata, MULTI_STOP_PREPARE);
+
+ if (cpu1 > cpu2)
+ swap(cpu1, cpu2);
+ if (cpu_stop_queue_two_works(cpu1, &work1, cpu2, &work2))
+ return -ENOENT;
+
+ wait_for_completion(&done.completion);
+ return done.ret;
+}
+
+/**
+ * stop_one_cpu_nowait - stop a cpu but don't wait for completion
+ * @cpu: cpu to stop
+ * @fn: function to execute
+ * @arg: argument to @fn
+ * @work_buf: pointer to cpu_stop_work structure
+ *
+ * Similar to stop_one_cpu() but doesn't wait for completion. The
+ * caller is responsible for ensuring @work_buf is currently unused
+ * and will remain untouched until stopper starts executing @fn.
+ *
+ * CONTEXT:
+ * Don't care.
+ *
+ * RETURNS:
+ * true if cpu_stop_work was queued successfully and @fn will be called,
+ * false otherwise.
+ */
+bool stop_one_cpu_nowait(unsigned int cpu, cpu_stop_fn_t fn, void *arg,
+ struct cpu_stop_work *work_buf)
+{
+ *work_buf = (struct cpu_stop_work){ .fn = fn, .arg = arg, };
+ return cpu_stop_queue_work(cpu, work_buf);
+}
+
+static bool queue_stop_cpus_work(const struct cpumask *cpumask,
+ cpu_stop_fn_t fn, void *arg,
+ struct cpu_stop_done *done)
+{
+ struct cpu_stop_work *work;
+ unsigned int cpu;
+ bool queued = false;
+
+ /*
+ * Disable preemption while queueing to avoid getting
+ * preempted by a stopper which might wait for other stoppers
+ * to enter @fn which can lead to deadlock.
+ */
+ preempt_disable();
+ stop_cpus_in_progress = true;
+ for_each_cpu(cpu, cpumask) {
+ work = &per_cpu(cpu_stopper.stop_work, cpu);
+ work->fn = fn;
+ work->arg = arg;
+ work->done = done;
+ if (cpu_stop_queue_work(cpu, work))
+ queued = true;
+ }
+ stop_cpus_in_progress = false;
+ preempt_enable();
+
+ return queued;
+}
+
+static int __stop_cpus(const struct cpumask *cpumask,
+ cpu_stop_fn_t fn, void *arg)
+{
+ struct cpu_stop_done done;
+
+ cpu_stop_init_done(&done, cpumask_weight(cpumask));
+ if (!queue_stop_cpus_work(cpumask, fn, arg, &done))
+ return -ENOENT;
+ wait_for_completion(&done.completion);
+ return done.ret;
+}
+
+/**
+ * stop_cpus - stop multiple cpus
+ * @cpumask: cpus to stop
+ * @fn: function to execute
+ * @arg: argument to @fn
+ *
+ * Execute @fn(@arg) on online cpus in @cpumask. On each target cpu,
+ * @fn is run in a process context with the highest priority
+ * preempting any task on the cpu and monopolizing it. This function
+ * returns after all executions are complete.
+ *
+ * This function doesn't guarantee the cpus in @cpumask stay online
+ * till @fn completes. If some cpus go down in the middle, execution
+ * on the cpu may happen partially or fully on different cpus. @fn
+ * should either be ready for that or the caller should ensure that
+ * the cpus stay online until this function completes.
+ *
+ * All stop_cpus() calls are serialized making it safe for @fn to wait
+ * for all cpus to start executing it.
+ *
+ * CONTEXT:
+ * Might sleep.
+ *
+ * RETURNS:
+ * -ENOENT if @fn(@arg) was not executed at all because all cpus in
+ * @cpumask were offline; otherwise, 0 if all executions of @fn
+ * returned 0, any non zero return value if any returned non zero.
+ */
+int stop_cpus(const struct cpumask *cpumask, cpu_stop_fn_t fn, void *arg)
+{
+ int ret;
+
+ /* static works are used, process one request at a time */
+ mutex_lock(&stop_cpus_mutex);
+ ret = __stop_cpus(cpumask, fn, arg);
+ mutex_unlock(&stop_cpus_mutex);
+ return ret;
+}
+
+/**
+ * try_stop_cpus - try to stop multiple cpus
+ * @cpumask: cpus to stop
+ * @fn: function to execute
+ * @arg: argument to @fn
+ *
+ * Identical to stop_cpus() except that it fails with -EAGAIN if
+ * someone else is already using the facility.
+ *
+ * CONTEXT:
+ * Might sleep.
+ *
+ * RETURNS:
+ * -EAGAIN if someone else is already stopping cpus, -ENOENT if
+ * @fn(@arg) was not executed at all because all cpus in @cpumask were
+ * offline; otherwise, 0 if all executions of @fn returned 0, any non
+ * zero return value if any returned non zero.
+ */
+int try_stop_cpus(const struct cpumask *cpumask, cpu_stop_fn_t fn, void *arg)
+{
+ int ret;
+
+ /* static works are used, process one request at a time */
+ if (!mutex_trylock(&stop_cpus_mutex))
+ return -EAGAIN;
+ ret = __stop_cpus(cpumask, fn, arg);
+ mutex_unlock(&stop_cpus_mutex);
+ return ret;
+}
+
+static int cpu_stop_should_run(unsigned int cpu)
+{
+ struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
+ unsigned long flags;
+ int run;
+
+ raw_spin_lock_irqsave(&stopper->lock, flags);
+ run = !list_empty(&stopper->works);
+ raw_spin_unlock_irqrestore(&stopper->lock, flags);
+ return run;
+}
+
+static void cpu_stopper_thread(unsigned int cpu)
+{
+ struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
+ struct cpu_stop_work *work;
+
+repeat:
+ work = NULL;
+ raw_spin_lock_irq(&stopper->lock);
+ if (!list_empty(&stopper->works)) {
+ work = list_first_entry(&stopper->works,
+ struct cpu_stop_work, list);
+ list_del_init(&work->list);
+ }
+ raw_spin_unlock_irq(&stopper->lock);
+
+ if (work) {
+ cpu_stop_fn_t fn = work->fn;
+ void *arg = work->arg;
+ struct cpu_stop_done *done = work->done;
+ int ret;
+
+ /* cpu stop callbacks must not sleep, make in_atomic() == T */
+ preempt_count_inc();
+ ret = fn(arg);
+ if (done) {
+ if (ret)
+ done->ret = ret;
+ cpu_stop_signal_done(done);
+ }
+ preempt_count_dec();
+ WARN_ONCE(preempt_count(),
+ "cpu_stop: %pf(%p) leaked preempt count\n", fn, arg);
+ goto repeat;
+ }
+}
+
+void stop_machine_park(int cpu)
+{
+ struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
+ /*
+ * Lockless. cpu_stopper_thread() will take stopper->lock and flush
+ * the pending works before it parks, until then it is fine to queue
+ * the new works.
+ */
+ stopper->enabled = false;
+ kthread_park(stopper->thread);
+}
+
+extern void sched_set_stop_task(int cpu, struct task_struct *stop);
+
+static void cpu_stop_create(unsigned int cpu)
+{
+ sched_set_stop_task(cpu, per_cpu(cpu_stopper.thread, cpu));
+}
+
+static void cpu_stop_park(unsigned int cpu)
+{
+ struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
+
+ WARN_ON(!list_empty(&stopper->works));
+}
+
+void stop_machine_unpark(int cpu)
+{
+ struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
+
+ stopper->enabled = true;
+ kthread_unpark(stopper->thread);
+}
+
+static struct smp_hotplug_thread cpu_stop_threads = {
+ .store = &cpu_stopper.thread,
+ .thread_should_run = cpu_stop_should_run,
+ .thread_fn = cpu_stopper_thread,
+ .thread_comm = "migration/%u",
+ .create = cpu_stop_create,
+ .park = cpu_stop_park,
+ .selfparking = true,
+};
+
+static int __init cpu_stop_init(void)
+{
+ unsigned int cpu;
+
+ for_each_possible_cpu(cpu) {
+ struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
+
+ raw_spin_lock_init(&stopper->lock);
+ INIT_LIST_HEAD(&stopper->works);
+ }
+
+ BUG_ON(smpboot_register_percpu_thread(&cpu_stop_threads));
+ stop_machine_unpark(raw_smp_processor_id());
+ stop_machine_initialized = true;
+ return 0;
+}
+early_initcall(cpu_stop_init);
+
+int stop_machine_cpuslocked(cpu_stop_fn_t fn, void *data,
+ const struct cpumask *cpus)
+{
+ struct multi_stop_data msdata = {
+ .fn = fn,
+ .data = data,
+ .num_threads = num_online_cpus(),
+ .active_cpus = cpus,
+ };
+
+ lockdep_assert_cpus_held();
+
+ if (!stop_machine_initialized) {
+ /*
+ * Handle the case where stop_machine() is called
+ * early in boot before stop_machine() has been
+ * initialized.
+ */
+ unsigned long flags;
+ int ret;
+
+ WARN_ON_ONCE(msdata.num_threads != 1);
+
+ local_irq_save(flags);
+ hard_irq_disable();
+ ret = (*fn)(data);
+ local_irq_restore(flags);
+
+ return ret;
+ }
+
+ /* Set the initial state and stop all online cpus. */
+ set_state(&msdata, MULTI_STOP_PREPARE);
+ return stop_cpus(cpu_online_mask, multi_cpu_stop, &msdata);
+}
+
+int stop_machine(cpu_stop_fn_t fn, void *data, const struct cpumask *cpus)
+{
+ int ret;
+
+ /* No CPUs can come up or down during this. */
+ cpus_read_lock();
+ ret = stop_machine_cpuslocked(fn, data, cpus);
+ cpus_read_unlock();
+ return ret;
+}
+EXPORT_SYMBOL_GPL(stop_machine);
+
+/**
+ * stop_machine_from_inactive_cpu - stop_machine() from inactive CPU
+ * @fn: the function to run
+ * @data: the data ptr for the @fn()
+ * @cpus: the cpus to run the @fn() on (NULL = any online cpu)
+ *
+ * This is identical to stop_machine() but can be called from a CPU which
+ * is not active. The local CPU is in the process of hotplug (so no other
+ * CPU hotplug can start) and not marked active and doesn't have enough
+ * context to sleep.
+ *
+ * This function provides stop_machine() functionality for such state by
+ * using busy-wait for synchronization and executing @fn directly for local
+ * CPU.
+ *
+ * CONTEXT:
+ * Local CPU is inactive. Temporarily stops all active CPUs.
+ *
+ * RETURNS:
+ * 0 if all executions of @fn returned 0, any non zero return value if any
+ * returned non zero.
+ */
+int stop_machine_from_inactive_cpu(cpu_stop_fn_t fn, void *data,
+ const struct cpumask *cpus)
+{
+ struct multi_stop_data msdata = { .fn = fn, .data = data,
+ .active_cpus = cpus };
+ struct cpu_stop_done done;
+ int ret;
+
+ /* Local CPU must be inactive and CPU hotplug in progress. */
+ BUG_ON(cpu_active(raw_smp_processor_id()));
+ msdata.num_threads = num_active_cpus() + 1; /* +1 for local */
+
+ /* No proper task established and can't sleep - busy wait for lock. */
+ while (!mutex_trylock(&stop_cpus_mutex))
+ cpu_relax();
+
+ /* Schedule work on other CPUs and execute directly for local CPU */
+ set_state(&msdata, MULTI_STOP_PREPARE);
+ cpu_stop_init_done(&done, num_active_cpus());
+ queue_stop_cpus_work(cpu_active_mask, multi_cpu_stop, &msdata,
+ &done);
+ ret = multi_cpu_stop(&msdata);
+
+ /* Busy wait for completion. */
+ while (!completion_done(&done.completion))
+ cpu_relax();
+
+ mutex_unlock(&stop_cpus_mutex);
+ return ret ?: done.ret;
+}