linux/kernel/stop_machine.c
Isaac J. Manjarres 9fb8d5dc4b stop_machine: Disable preemption when waking two stopper threads
When cpu_stop_queue_two_works() begins to wake the stopper threads, it does
so without preemption disabled, which leads to the following race
condition:

The source CPU calls cpu_stop_queue_two_works(), with cpu1 as the source
CPU, and cpu2 as the destination CPU. When adding the stopper threads to
the wake queue used in this function, the source CPU stopper thread is
added first, and the destination CPU stopper thread is added last.

When wake_up_q() is invoked to wake the stopper threads, the threads are
woken up in the order that they are queued in, so the source CPU's stopper
thread is woken up first, and it preempts the thread running on the source
CPU.

The stopper thread will then execute on the source CPU, disable preemption,
and begin executing multi_cpu_stop(), and wait for an ack from the
destination CPU's stopper thread, with preemption still disabled. Since the
worker thread that woke up the stopper thread on the source CPU is affine
to the source CPU, and preemption is disabled on the source CPU, that
thread will never run to dequeue the destination CPU's stopper thread from
the wake queue, and thus, the destination CPU's stopper thread will never
run, causing the source CPU's stopper thread to wait forever, and stall.

Disable preemption when waking the stopper threads in
cpu_stop_queue_two_works().

Fixes: 0b26351b91 ("stop_machine, sched: Fix migrate_swap() vs. active_balance() deadlock")
Co-Developed-by: Prasad Sodagudi <psodagud@codeaurora.org>
Signed-off-by: Prasad Sodagudi <psodagud@codeaurora.org>
Co-Developed-by: Pavankumar Kondeti <pkondeti@codeaurora.org>
Signed-off-by: Pavankumar Kondeti <pkondeti@codeaurora.org>
Signed-off-by: Isaac J. Manjarres <isaacm@codeaurora.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: peterz@infradead.org
Cc: matt@codeblueprint.co.uk
Cc: bigeasy@linutronix.de
Cc: gregkh@linuxfoundation.org
Cc: stable@vger.kernel.org
Link: https://lkml.kernel.org/r/1530655334-4601-1-git-send-email-isaacm@codeaurora.org
2018-07-15 12:12:45 +02:00

668 lines
17 KiB
C

/*
* 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;
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);
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:
raw_spin_lock_irq(&stopper1->lock);
raw_spin_lock_nested(&stopper2->lock, SINGLE_DEPTH_NESTING);
err = -ENOENT;
if (!stopper1->enabled || !stopper2->enabled)
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().
*/
err = -EDEADLK;
if (unlikely(stop_cpus_in_progress))
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)) {
while (stop_cpus_in_progress)
cpu_relax();
goto retry;
}
if (!err) {
preempt_disable();
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;
}