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Message-Id: <20210216103506.416286-4-vincent.donnefort@arm.com>
Date: Tue, 16 Feb 2021 10:35:06 +0000
From: vincent.donnefort@....com
To: peterz@...radead.org, tglx@...utronix.de
Cc: linux-kernel@...r.kernel.org, valentin.schneider@....com,
Vincent Donnefort <vincent.donnefort@....com>
Subject: [PATCH v2 3/3] cpu/hotplug: Add cpuhp_invoke_callback_range()
From: Vincent Donnefort <vincent.donnefort@....com>
Factorizing and unifying cpuhp callback range invocations, especially for
the hotunplug path, where two different ways of decrementing were used. The
first one, decrements before the callback is called:
cpuhp_thread_fun()
state = st->state;
st->state--;
cpuhp_invoke_callback(state);
The second one, after:
take_down_cpu()|cpuhp_down_callbacks()
cpuhp_invoke_callback(st->state);
st->state--;
This is problematic for rolling back the steps in case of error, as
depending on the decrement, the rollback will start from N or N-1. It also
makes tracing inconsistent, between steps run in the cpuhp thread and
the others.
Additionally, avoid useless cpuhp_thread_fun() loops by skipping empty
steps.
Signed-off-by: Vincent Donnefort <vincent.donnefort@....com>
diff --git a/kernel/cpu.c b/kernel/cpu.c
index d44877095b8c..382ef48e1271 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -135,6 +135,11 @@ static struct cpuhp_step *cpuhp_get_step(enum cpuhp_state state)
return cpuhp_hp_states + state;
}
+static bool cpuhp_step_empty(bool bringup, struct cpuhp_step *step)
+{
+ return bringup ? !step->startup.single : !step->teardown.single;
+}
+
/**
* cpuhp_invoke_callback _ Invoke the callbacks for a given state
* @cpu: The cpu for which the callback should be invoked
@@ -157,26 +162,24 @@ static int cpuhp_invoke_callback(unsigned int cpu, enum cpuhp_state state,
if (st->fail == state) {
st->fail = CPUHP_INVALID;
-
- if (!(bringup ? step->startup.single : step->teardown.single))
- return 0;
-
return -EAGAIN;
}
+ if (cpuhp_step_empty(bringup, step)) {
+ WARN_ON_ONCE(1);
+ return 0;
+ }
+
if (!step->multi_instance) {
WARN_ON_ONCE(lastp && *lastp);
cb = bringup ? step->startup.single : step->teardown.single;
- if (!cb)
- return 0;
+
trace_cpuhp_enter(cpu, st->target, state, cb);
ret = cb(cpu);
trace_cpuhp_exit(cpu, st->state, state, ret);
return ret;
}
cbm = bringup ? step->startup.multi : step->teardown.multi;
- if (!cbm)
- return 0;
/* Single invocation for instance add/remove */
if (node) {
@@ -468,6 +471,15 @@ cpuhp_set_state(struct cpuhp_cpu_state *st, enum cpuhp_state target)
static inline void
cpuhp_reset_state(struct cpuhp_cpu_state *st, enum cpuhp_state prev_state)
{
+ st->target = prev_state;
+
+ /*
+ * Already rolling back. No need invert the bringup value or to change
+ * the current state.
+ */
+ if (st->rollback)
+ return;
+
st->rollback = true;
/*
@@ -481,7 +493,6 @@ cpuhp_reset_state(struct cpuhp_cpu_state *st, enum cpuhp_state prev_state)
st->state++;
}
- st->target = prev_state;
st->bringup = !st->bringup;
}
@@ -584,10 +595,53 @@ static int finish_cpu(unsigned int cpu)
* Hotplug state machine related functions
*/
-static void undo_cpu_up(unsigned int cpu, struct cpuhp_cpu_state *st)
+/*
+ * Get the next state to run. Empty ones will be skipped. Returns true if a
+ * state must be run.
+ *
+ * st->state will be modified ahead of time, to match state_to_run, as if it
+ * has already ran.
+ */
+static bool cpuhp_next_state(bool bringup,
+ enum cpuhp_state *state_to_run,
+ struct cpuhp_cpu_state *st,
+ enum cpuhp_state target)
{
- for (st->state--; st->state > st->target; st->state--)
- cpuhp_invoke_callback(cpu, st->state, false, NULL, NULL);
+ do {
+ if (bringup) {
+ if (st->state >= target)
+ return false;
+
+ *state_to_run = ++st->state;
+ } else {
+ if (st->state <= target)
+ return false;
+
+ *state_to_run = st->state--;
+ }
+
+ if (!cpuhp_step_empty(bringup, cpuhp_get_step(*state_to_run)))
+ break;
+ } while (true);
+
+ return true;
+}
+
+static int cpuhp_invoke_callback_range(bool bringup,
+ unsigned int cpu,
+ struct cpuhp_cpu_state *st,
+ enum cpuhp_state target)
+{
+ enum cpuhp_state state;
+ int err = 0;
+
+ while (cpuhp_next_state(bringup, &state, st, target)) {
+ err = cpuhp_invoke_callback(cpu, state, bringup, NULL, NULL);
+ if (err)
+ break;
+ }
+
+ return err;
}
static inline bool can_rollback_cpu(struct cpuhp_cpu_state *st)
@@ -610,16 +664,12 @@ static int cpuhp_up_callbacks(unsigned int cpu, struct cpuhp_cpu_state *st,
enum cpuhp_state prev_state = st->state;
int ret = 0;
- while (st->state < target) {
- st->state++;
- ret = cpuhp_invoke_callback(cpu, st->state, true, NULL, NULL);
- if (ret) {
- if (can_rollback_cpu(st)) {
- st->target = prev_state;
- undo_cpu_up(cpu, st);
- }
- break;
- }
+ ret = cpuhp_invoke_callback_range(true, cpu, st, target);
+ if (ret) {
+ cpuhp_reset_state(st, prev_state);
+ if (can_rollback_cpu(st))
+ WARN_ON(cpuhp_invoke_callback_range(false, cpu, st,
+ prev_state));
}
return ret;
}
@@ -683,17 +733,9 @@ static void cpuhp_thread_fun(unsigned int cpu)
state = st->cb_state;
st->should_run = false;
} else {
- 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);
- }
+ st->should_run = cpuhp_next_state(bringup, &state, st, st->target);
+ if (!st->should_run)
+ goto end;
}
WARN_ON_ONCE(!cpuhp_is_ap_state(state));
@@ -721,6 +763,7 @@ static void cpuhp_thread_fun(unsigned int cpu)
st->should_run = false;
}
+end:
cpuhp_lock_release(bringup);
lockdep_release_cpus_lock();
@@ -874,19 +917,18 @@ static int take_cpu_down(void *_param)
return err;
/*
- * We get here while we are in CPUHP_TEARDOWN_CPU state and we must not
- * do this step again.
+ * Must be called from CPUHP_TEARDOWN_CPU, which means, as we are going
+ * down, that the current state is CPUHP_TEARDOWN_CPU - 1.
*/
- WARN_ON(st->state != CPUHP_TEARDOWN_CPU);
- st->state--;
+ WARN_ON(st->state != (CPUHP_TEARDOWN_CPU - 1));
+
/* Invoke the former CPU_DYING callbacks */
- for (; st->state > target; st->state--) {
- ret = cpuhp_invoke_callback(cpu, st->state, false, NULL, NULL);
- /*
- * DYING must not fail!
- */
- WARN_ON_ONCE(ret);
- }
+ ret = cpuhp_invoke_callback_range(false, cpu, st, target);
+
+ /*
+ * DYING must not fail!
+ */
+ WARN_ON_ONCE(ret);
/* Give up timekeeping duties */
tick_handover_do_timer();
@@ -968,27 +1010,22 @@ void cpuhp_report_idle_dead(void)
cpuhp_complete_idle_dead, st, 0);
}
-static void undo_cpu_down(unsigned int cpu, struct cpuhp_cpu_state *st)
-{
- for (st->state++; st->state < st->target; st->state++)
- 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;
- if (st->state < prev_state)
- undo_cpu_down(cpu, st);
- break;
- }
+ ret = cpuhp_invoke_callback_range(false, cpu, st, target);
+ if (ret) {
+
+ cpuhp_reset_state(st, prev_state);
+
+ if (st->state < prev_state)
+ WARN_ON(cpuhp_invoke_callback_range(true, cpu, st,
+ prev_state));
}
+
return ret;
}
@@ -1161,14 +1198,12 @@ void notify_cpu_starting(unsigned int cpu)
rcu_cpu_starting(cpu); /* Enables RCU usage on this CPU. */
cpumask_set_cpu(cpu, &cpus_booted_once_mask);
- while (st->state < target) {
- st->state++;
- ret = cpuhp_invoke_callback(cpu, st->state, true, NULL, NULL);
- /*
- * STARTING must not fail!
- */
- WARN_ON_ONCE(ret);
- }
+ ret = cpuhp_invoke_callback_range(true, cpu, st, target);
+
+ /*
+ * STARTING must not fail!
+ */
+ WARN_ON_ONCE(ret);
}
/*
@@ -1774,8 +1809,7 @@ static int cpuhp_issue_call(int cpu, enum cpuhp_state state, bool bringup,
* If there's nothing to do, we done.
* Relies on the union for multi_instance.
*/
- if ((bringup && !sp->startup.single) ||
- (!bringup && !sp->teardown.single))
+ if (cpuhp_step_empty(bringup, sp))
return 0;
/*
* The non AP bound callbacks can fail on bringup. On teardown
--
2.25.1
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