smp/hotplug: Rewrite AP state machine core

There is currently no explicit state change on rollback. That is,
st->bringup, st->rollback and st->target are not consistent when doing
the rollback.

Rework the AP state handling to be more coherent. This does mean we
have to do a second AP kick-and-wait for rollback, but since rollback
is the slow path of a slowpath, this really should not matter.

Take this opportunity to simplify the AP thread function to only run a
single callback per invocation. This unifies the three single/up/down
modes is supports. The looping it used to do for up/down are achieved
by retaining should_run and relying on the main smpboot_thread_fn()
loop.

(I have most of a patch that does the same for the BP state handling,
but that's not critical and gets a little complicated because
CPUHP_BRINGUP_CPU does the AP handoff from a callback, which gets
recursive @st usage, I still have de-fugly that.)

[ tglx: Move cpuhp_down_callbacks() et al. into the HOTPLUG_CPU section to
  	avoid gcc complaining about unused functions. Make the HOTPLUG_CPU
  	one piece instead of having two consecutive ifdef sections of the
  	same type. ]

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: bigeasy@linutronix.de
Cc: efault@gmx.de
Cc: rostedt@goodmis.org
Cc: max.byungchul.park@gmail.com
Link: https://lkml.kernel.org/r/20170920170546.769658088@infradead.org
This commit is contained in:
Peter Zijlstra 2017-09-20 19:00:17 +02:00 committed by Thomas Gleixner
parent 96abb96854
commit 4dddfb5faa

View File

@ -58,6 +58,7 @@ struct cpuhp_cpu_state {
bool single;
bool bringup;
struct hlist_node *node;
struct hlist_node *last;
enum cpuhp_state cb_state;
int result;
struct completion done;
@ -112,6 +113,14 @@ static bool cpuhp_is_ap_state(enum cpuhp_state state)
return state > CPUHP_BRINGUP_CPU && state != CPUHP_TEARDOWN_CPU;
}
/*
* The former STARTING/DYING states, ran with IRQs disabled and must not fail.
*/
static bool cpuhp_is_atomic_state(enum cpuhp_state state)
{
return CPUHP_AP_IDLE_DEAD <= state && state < CPUHP_AP_ONLINE;
}
static struct cpuhp_step *cpuhp_get_step(enum cpuhp_state state)
{
struct cpuhp_step *sp;
@ -286,7 +295,72 @@ void cpu_hotplug_enable(void)
EXPORT_SYMBOL_GPL(cpu_hotplug_enable);
#endif /* CONFIG_HOTPLUG_CPU */
static void __cpuhp_kick_ap_work(struct cpuhp_cpu_state *st);
static inline enum cpuhp_state
cpuhp_set_state(struct cpuhp_cpu_state *st, enum cpuhp_state target)
{
enum cpuhp_state prev_state = st->state;
st->rollback = false;
st->last = NULL;
st->target = target;
st->single = false;
st->bringup = st->state < target;
return prev_state;
}
static inline void
cpuhp_reset_state(struct cpuhp_cpu_state *st, enum cpuhp_state prev_state)
{
st->rollback = true;
/*
* If we have st->last we need to undo partial multi_instance of this
* state first. Otherwise start undo at the previous state.
*/
if (!st->last) {
if (st->bringup)
st->state--;
else
st->state++;
}
st->target = prev_state;
st->bringup = !st->bringup;
}
/* Regular hotplug invocation of the AP hotplug thread */
static void __cpuhp_kick_ap(struct cpuhp_cpu_state *st)
{
if (!st->single && st->state == st->target)
return;
st->result = 0;
/*
* Make sure the above stores are visible before should_run becomes
* true. Paired with the mb() above in cpuhp_thread_fun()
*/
smp_mb();
st->should_run = true;
wake_up_process(st->thread);
wait_for_completion(&st->done);
}
static int cpuhp_kick_ap(struct cpuhp_cpu_state *st, enum cpuhp_state target)
{
enum cpuhp_state prev_state;
int ret;
prev_state = cpuhp_set_state(st, target);
__cpuhp_kick_ap(st);
if ((ret = st->result)) {
cpuhp_reset_state(st, prev_state);
__cpuhp_kick_ap(st);
}
return ret;
}
static int bringup_wait_for_ap(unsigned int cpu)
{
@ -301,12 +375,10 @@ static int bringup_wait_for_ap(unsigned int cpu)
stop_machine_unpark(cpu);
kthread_unpark(st->thread);
/* Should we go further up ? */
if (st->target > CPUHP_AP_ONLINE_IDLE) {
__cpuhp_kick_ap_work(st);
wait_for_completion(&st->done);
}
return st->result;
if (st->target <= CPUHP_AP_ONLINE_IDLE)
return 0;
return cpuhp_kick_ap(st, st->target);
}
static int bringup_cpu(unsigned int cpu)
@ -332,32 +404,6 @@ static int bringup_cpu(unsigned int cpu)
/*
* Hotplug state machine related functions
*/
static void undo_cpu_down(unsigned int cpu, struct cpuhp_cpu_state *st)
{
for (st->state++; st->state < st->target; st->state++) {
struct cpuhp_step *step = cpuhp_get_step(st->state);
if (!step->skip_onerr)
cpuhp_invoke_callback(cpu, st->state, true, NULL, NULL);
}
}
static int cpuhp_down_callbacks(unsigned int cpu, struct cpuhp_cpu_state *st,
enum cpuhp_state target)
{
enum cpuhp_state prev_state = st->state;
int ret = 0;
for (; st->state > target; st->state--) {
ret = cpuhp_invoke_callback(cpu, st->state, false, NULL, NULL);
if (ret) {
st->target = prev_state;
undo_cpu_down(cpu, st);
break;
}
}
return ret;
}
static void undo_cpu_up(unsigned int cpu, struct cpuhp_cpu_state *st)
{
@ -404,71 +450,90 @@ static int cpuhp_should_run(unsigned int cpu)
return st->should_run;
}
/* Execute the teardown callbacks. Used to be CPU_DOWN_PREPARE */
static int cpuhp_ap_offline(unsigned int cpu, struct cpuhp_cpu_state *st)
{
enum cpuhp_state target = max((int)st->target, CPUHP_TEARDOWN_CPU);
return cpuhp_down_callbacks(cpu, st, target);
}
/* Execute the online startup callbacks. Used to be CPU_ONLINE */
static int cpuhp_ap_online(unsigned int cpu, struct cpuhp_cpu_state *st)
{
return cpuhp_up_callbacks(cpu, st, st->target);
}
/*
* Execute teardown/startup callbacks on the plugged cpu. Also used to invoke
* callbacks when a state gets [un]installed at runtime.
*
* Each invocation of this function by the smpboot thread does a single AP
* state callback.
*
* It has 3 modes of operation:
* - single: runs st->cb_state
* - up: runs ++st->state, while st->state < st->target
* - down: runs st->state--, while st->state > st->target
*
* When complete or on error, should_run is cleared and the completion is fired.
*/
static void cpuhp_thread_fun(unsigned int cpu)
{
struct cpuhp_cpu_state *st = this_cpu_ptr(&cpuhp_state);
int ret = 0;
bool bringup = st->bringup;
enum cpuhp_state state;
/*
* Paired with the mb() in cpuhp_kick_ap_work and
* cpuhp_invoke_ap_callback, so the work set is consistent visible.
* ACQUIRE for the cpuhp_should_run() load of ->should_run. Ensures
* that if we see ->should_run we also see the rest of the state.
*/
smp_mb();
if (!st->should_run)
if (WARN_ON_ONCE(!st->should_run))
return;
st->should_run = false;
lock_map_acquire(&cpuhp_state_lock_map);
/* Single callback invocation for [un]install ? */
if (st->single) {
if (st->cb_state < CPUHP_AP_ONLINE) {
local_irq_disable();
ret = cpuhp_invoke_callback(cpu, st->cb_state,
st->bringup, st->node,
NULL);
local_irq_enable();
} else {
ret = cpuhp_invoke_callback(cpu, st->cb_state,
st->bringup, st->node,
NULL);
}
} else if (st->rollback) {
BUG_ON(st->state < CPUHP_AP_ONLINE_IDLE);
undo_cpu_down(cpu, st);
st->rollback = false;
state = st->cb_state;
st->should_run = false;
} else {
/* Cannot happen .... */
BUG_ON(st->state < CPUHP_AP_ONLINE_IDLE);
/* Regular hotplug work */
if (st->state < st->target)
ret = cpuhp_ap_online(cpu, st);
else if (st->state > st->target)
ret = cpuhp_ap_offline(cpu, st);
if (bringup) {
st->state++;
state = st->state;
st->should_run = (st->state < st->target);
WARN_ON_ONCE(st->state > st->target);
} else {
state = st->state;
st->state--;
st->should_run = (st->state > st->target);
WARN_ON_ONCE(st->state < st->target);
}
}
WARN_ON_ONCE(!cpuhp_is_ap_state(state));
if (st->rollback) {
struct cpuhp_step *step = cpuhp_get_step(state);
if (step->skip_onerr)
goto next;
}
if (cpuhp_is_atomic_state(state)) {
local_irq_disable();
st->result = cpuhp_invoke_callback(cpu, state, bringup, st->node, &st->last);
local_irq_enable();
/*
* STARTING/DYING must not fail!
*/
WARN_ON_ONCE(st->result);
} else {
st->result = cpuhp_invoke_callback(cpu, state, bringup, st->node, &st->last);
}
if (st->result) {
/*
* If we fail on a rollback, we're up a creek without no
* paddle, no way forward, no way back. We loose, thanks for
* playing.
*/
WARN_ON_ONCE(st->rollback);
st->should_run = false;
}
next:
lock_map_release(&cpuhp_state_lock_map);
st->result = ret;
complete(&st->done);
if (!st->should_run)
complete(&st->done);
}
/* Invoke a single callback on a remote cpu */
@ -477,6 +542,7 @@ cpuhp_invoke_ap_callback(int cpu, enum cpuhp_state state, bool bringup,
struct hlist_node *node)
{
struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, cpu);
int ret;
if (!cpu_online(cpu))
return 0;
@ -491,48 +557,43 @@ cpuhp_invoke_ap_callback(int cpu, enum cpuhp_state state, bool bringup,
if (!st->thread)
return cpuhp_invoke_callback(cpu, state, bringup, node, NULL);
st->rollback = false;
st->last = NULL;
st->node = node;
st->bringup = bringup;
st->cb_state = state;
st->single = true;
st->bringup = bringup;
st->node = node;
__cpuhp_kick_ap(st);
/*
* Make sure the above stores are visible before should_run becomes
* true. Paired with the mb() above in cpuhp_thread_fun()
* If we failed and did a partial, do a rollback.
*/
smp_mb();
st->should_run = true;
wake_up_process(st->thread);
wait_for_completion(&st->done);
return st->result;
}
if ((ret = st->result) && st->last) {
st->rollback = true;
st->bringup = !bringup;
/* Regular hotplug invocation of the AP hotplug thread */
static void __cpuhp_kick_ap_work(struct cpuhp_cpu_state *st)
{
st->result = 0;
st->single = false;
/*
* Make sure the above stores are visible before should_run becomes
* true. Paired with the mb() above in cpuhp_thread_fun()
*/
smp_mb();
st->should_run = true;
wake_up_process(st->thread);
__cpuhp_kick_ap(st);
}
return ret;
}
static int cpuhp_kick_ap_work(unsigned int cpu)
{
struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, cpu);
enum cpuhp_state state = st->state;
enum cpuhp_state prev_state = st->state;
int ret;
trace_cpuhp_enter(cpu, st->target, state, cpuhp_kick_ap_work);
lock_map_acquire(&cpuhp_state_lock_map);
lock_map_release(&cpuhp_state_lock_map);
__cpuhp_kick_ap_work(st);
wait_for_completion(&st->done);
trace_cpuhp_exit(cpu, st->state, state, st->result);
return st->result;
trace_cpuhp_enter(cpu, st->target, prev_state, cpuhp_kick_ap_work);
ret = cpuhp_kick_ap(st, st->target);
trace_cpuhp_exit(cpu, st->state, prev_state, ret);
return ret;
}
static struct smp_hotplug_thread cpuhp_threads = {
@ -693,11 +754,32 @@ void cpuhp_report_idle_dead(void)
cpuhp_complete_idle_dead, st, 0);
}
#else
#define takedown_cpu NULL
#endif
static void undo_cpu_down(unsigned int cpu, struct cpuhp_cpu_state *st)
{
for (st->state++; st->state < st->target; st->state++) {
struct cpuhp_step *step = cpuhp_get_step(st->state);
#ifdef CONFIG_HOTPLUG_CPU
if (!step->skip_onerr)
cpuhp_invoke_callback(cpu, st->state, true, NULL, NULL);
}
}
static int cpuhp_down_callbacks(unsigned int cpu, struct cpuhp_cpu_state *st,
enum cpuhp_state target)
{
enum cpuhp_state prev_state = st->state;
int ret = 0;
for (; st->state > target; st->state--) {
ret = cpuhp_invoke_callback(cpu, st->state, false, NULL, NULL);
if (ret) {
st->target = prev_state;
undo_cpu_down(cpu, st);
break;
}
}
return ret;
}
/* Requires cpu_add_remove_lock to be held */
static int __ref _cpu_down(unsigned int cpu, int tasks_frozen,
@ -716,13 +798,13 @@ static int __ref _cpu_down(unsigned int cpu, int tasks_frozen,
cpuhp_tasks_frozen = tasks_frozen;
prev_state = st->state;
st->target = target;
prev_state = cpuhp_set_state(st, target);
/*
* If the current CPU state is in the range of the AP hotplug thread,
* then we need to kick the thread.
*/
if (st->state > CPUHP_TEARDOWN_CPU) {
st->target = max((int)target, CPUHP_TEARDOWN_CPU);
ret = cpuhp_kick_ap_work(cpu);
/*
* The AP side has done the error rollback already. Just
@ -737,6 +819,8 @@ static int __ref _cpu_down(unsigned int cpu, int tasks_frozen,
*/
if (st->state > CPUHP_TEARDOWN_CPU)
goto out;
st->target = target;
}
/*
* The AP brought itself down to CPUHP_TEARDOWN_CPU. So we need
@ -744,9 +828,8 @@ static int __ref _cpu_down(unsigned int cpu, int tasks_frozen,
*/
ret = cpuhp_down_callbacks(cpu, st, target);
if (ret && st->state > CPUHP_TEARDOWN_CPU && st->state < prev_state) {
st->target = prev_state;
st->rollback = true;
cpuhp_kick_ap_work(cpu);
cpuhp_reset_state(st, prev_state);
__cpuhp_kick_ap(st);
}
out:
@ -771,11 +854,15 @@ out:
cpu_maps_update_done();
return err;
}
int cpu_down(unsigned int cpu)
{
return do_cpu_down(cpu, CPUHP_OFFLINE);
}
EXPORT_SYMBOL(cpu_down);
#else
#define takedown_cpu NULL
#endif /*CONFIG_HOTPLUG_CPU*/
/**
@ -846,7 +933,7 @@ static int _cpu_up(unsigned int cpu, int tasks_frozen, enum cpuhp_state target)
cpuhp_tasks_frozen = tasks_frozen;
st->target = target;
cpuhp_set_state(st, target);
/*
* If the current CPU state is in the range of the AP hotplug thread,
* then we need to kick the thread once more.
@ -1313,6 +1400,10 @@ static int cpuhp_issue_call(int cpu, enum cpuhp_state state, bool bringup,
struct cpuhp_step *sp = cpuhp_get_step(state);
int ret;
/*
* If there's nothing to do, we done.
* Relies on the union for multi_instance.
*/
if ((bringup && !sp->startup.single) ||
(!bringup && !sp->teardown.single))
return 0;