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stop_machine: use workqueues instead of kernel threads 

Convert stop_machine to a workqueue based approach. Instead of using kernel
threads for stop_machine we now use a an rt workqueue to synchronize all
cpus.
This has the advantage that all needed per cpu threads are already created
when stop_machine gets called. And therefore a call to stop_machine won't
fail anymore. This is needed for s390 which needs a mechanism to synchronize
all cpus without allocating any memory.
As Rusty pointed out free_module() needs a non-failing stop_machine interface
as well.

As a side effect the stop_machine code gets simplified.

Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
This commit is contained in:
Heiko Carstens 2008-10-13 23:50:10 +02:00 committed by Rusty Russell
parent 0d557dc97f
commit c9583e55fa
1 changed files with 40 additions and 69 deletions
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109
kernel/stop_machine.c
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@ -37,9 +37,13 @@ struct stop_machine_data {
/* Like num_online_cpus(), but hotplug cpu uses us, so we need this. */
static unsigned int num_threads;
static atomic_t thread_ack;
static struct completion finished;
static DEFINE_MUTEX(lock);
static struct workqueue_struct *stop_machine_wq;
static struct stop_machine_data active, idle;
static const cpumask_t *active_cpus;
static void *stop_machine_work;
static void set_state(enum stopmachine_state newstate)
{
/* Reset ack counter. */
@ -51,21 +55,25 @@ static void set_state(enum stopmachine_state newstate)
/* Last one to ack a state moves to the next state. */
static void ack_state(void)
{
if (atomic_dec_and_test(&thread_ack)) {
/* If we're the last one to ack the EXIT, we're finished. */
if (state == STOPMACHINE_EXIT)
complete(&finished);
else
set_state(state + 1);
}
if (atomic_dec_and_test(&thread_ack))
set_state(state + 1);
}
/* This is the actual thread which stops the CPU. It exits by itself rather
* than waiting for kthread_stop(), because it's easier for hotplug CPU. */
static int stop_cpu(struct stop_machine_data *smdata)
/* This is the actual function which stops the CPU. It runs
* in the context of a dedicated stopmachine workqueue. */
static void stop_cpu(struct work_struct *unused)
{
enum stopmachine_state curstate = STOPMACHINE_NONE;
struct stop_machine_data *smdata = &idle;
int cpu = smp_processor_id();
if (!active_cpus) {
if (cpu == first_cpu(cpu_online_map))
smdata = &active;
} else {
if (cpu_isset(cpu, *active_cpus))
smdata = &active;
}
/* Simple state machine */
do {
/* Chill out and ensure we re-read stopmachine_state. */
@ -90,7 +98,6 @@ static int stop_cpu(struct stop_machine_data *smdata)
} while (curstate != STOPMACHINE_EXIT);
local_irq_enable();
do_exit(0);
}
/* Callback for CPUs which aren't supposed to do anything. */
@ -101,78 +108,34 @@ static int chill(void *unused)
int __stop_machine(int (*fn)(void *), void *data, const cpumask_t *cpus)
{
int i, err;
struct stop_machine_data active, idle;
struct task_struct **threads;
struct work_struct *sm_work;
int i;
/* Set up initial state. */
mutex_lock(&lock);
num_threads = num_online_cpus();
active_cpus = cpus;
active.fn = fn;
active.data = data;
active.fnret = 0;
idle.fn = chill;
idle.data = NULL;
/* This could be too big for stack on large machines. */
threads = kcalloc(NR_CPUS, sizeof(threads[0]), GFP_KERNEL);
if (!threads)
return -ENOMEM;
/* Set up initial state. */
mutex_lock(&lock);
init_completion(&finished);
num_threads = num_online_cpus();
set_state(STOPMACHINE_PREPARE);
for_each_online_cpu(i) {
struct stop_machine_data *smdata = &idle;
struct sched_param param = { .sched_priority = MAX_RT_PRIO-1 };
if (!cpus) {
if (i == first_cpu(cpu_online_map))
smdata = &active;
} else {
if (cpu_isset(i, *cpus))
smdata = &active;
}
threads[i] = kthread_create((void *)stop_cpu, smdata, "kstop%u",
i);
if (IS_ERR(threads[i])) {
err = PTR_ERR(threads[i]);
threads[i] = NULL;
goto kill_threads;
}
/* Place it onto correct cpu. */
kthread_bind(threads[i], i);
/* Make it highest prio. */
if (sched_setscheduler_nocheck(threads[i], SCHED_FIFO, &param))
BUG();
}
/* We've created all the threads. Wake them all: hold this CPU so one
/* Schedule the stop_cpu work on all cpus: hold this CPU so one
* doesn't hit this CPU until we're ready. */
get_cpu();
for_each_online_cpu(i)
wake_up_process(threads[i]);
for_each_online_cpu(i) {
sm_work = percpu_ptr(stop_machine_work, i);
INIT_WORK(sm_work, stop_cpu);
queue_work_on(i, stop_machine_wq, sm_work);
}
/* This will release the thread on our CPU. */
put_cpu();
wait_for_completion(&finished);
flush_workqueue(stop_machine_wq);
mutex_unlock(&lock);
kfree(threads);
return active.fnret;
kill_threads:
for_each_online_cpu(i)
if (threads[i])
kthread_stop(threads[i]);
mutex_unlock(&lock);
kfree(threads);
return err;
}
int stop_machine(int (*fn)(void *), void *data, const cpumask_t *cpus)
@ -187,3 +150,11 @@ int stop_machine(int (*fn)(void *), void *data, const cpumask_t *cpus)
return ret;
}
EXPORT_SYMBOL_GPL(stop_machine);
static int __init stop_machine_init(void)
{
stop_machine_wq = create_rt_workqueue("kstop");
stop_machine_work = alloc_percpu(struct work_struct);
return 0;
}
early_initcall(stop_machine_init);