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Subject[PATCH 5/7] smp/hotplug: Differentiate the AP completion between up and down
With lockdep-crossrelease we get deadlock reports that span cpu-up and
cpu-down chains. Such deadlocks cannot possibly happen because cpu-up
and cpu-down are globally serialized.

takedown_cpu()
irq_lock_sparse()
wait_for_completion(&st->done)

cpuhp_thread_fun
cpuhp_up_callback
cpuhp_invoke_callback
irq_affinity_online_cpu
irq_local_spare()
irq_unlock_sparse()
complete(&st->done)

Now that we have consistent AP state, we can trivially separate the
AP completion between up and down using st->bringup.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
kernel/cpu.c | 33 ++++++++++++++++++++++++---------
1 file changed, 24 insertions(+), 9 deletions(-)

--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -46,7 +46,8 @@
* @bringup: Single callback bringup or teardown selector
* @cb_state: The state for a single callback (install/uninstall)
* @result: Result of the operation
- * @done: Signal completion to the issuer of the task
+ * @done_up: Signal completion to the issuer of the task for cpu-up
+ * @done_down: Signal completion to the issuer of the task for cpu-down
*/
struct cpuhp_cpu_state {
enum cpuhp_state state;
@@ -61,7 +62,8 @@ struct cpuhp_cpu_state {
struct hlist_node *last;
enum cpuhp_state cb_state;
int result;
- struct completion done;
+ struct completion done_up;
+ struct completion done_down;
#endif
};

@@ -90,6 +92,18 @@ static void inline cpuhp_lock_release(bo

#endif

+static inline void wait_for_ap_thread(struct cpuhp_cpu_state *st, bool bringup)
+{
+ struct completion *done = bringup ? &st->done_up : &st->done_down;
+ wait_for_completion(done);
+}
+
+static inline void complete_ap_thread(struct cpuhp_cpu_state *st, bool bringup)
+{
+ struct completion *done = bringup ? &st->done_up : &st->done_down;
+ complete(done);
+}
+
/**
* cpuhp_step - Hotplug state machine step
* @name: Name of the step
@@ -368,7 +382,7 @@ static void __cpuhp_kick_ap(struct cpuhp
smp_mb();
st->should_run = true;
wake_up_process(st->thread);
- wait_for_completion(&st->done);
+ wait_for_ap_thread(st, st->bringup);
}

static int cpuhp_kick_ap(struct cpuhp_cpu_state *st, enum cpuhp_state target)
@@ -391,7 +405,7 @@ static int bringup_wait_for_ap(unsigned
struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, cpu);

/* Wait for the CPU to reach CPUHP_AP_ONLINE_IDLE */
- wait_for_completion(&st->done);
+ wait_for_ap_thread(st, true);
if (WARN_ON_ONCE((!cpu_online(cpu))))
return -ECANCELED;

@@ -490,7 +504,8 @@ static void cpuhp_create(unsigned int cp
{
struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, cpu);

- init_completion(&st->done);
+ init_completion(&st->done_up);
+ init_completion(&st->done_down);
}

static int cpuhp_should_run(unsigned int cpu)
@@ -584,7 +599,7 @@ static void cpuhp_thread_fun(unsigned in
cpuhp_lock_release(bringup);

if (!st->should_run)
- complete(&st->done);
+ complete_ap_thread(st, bringup);
}

/* Invoke a single callback on a remote cpu */
@@ -780,7 +795,7 @@ static int takedown_cpu(unsigned int cpu
*
* Wait for the stop thread to go away.
*/
- wait_for_completion(&st->done);
+ wait_for_ap_thread(st, false);
BUG_ON(st->state != CPUHP_AP_IDLE_DEAD);

/* Interrupts are moved away from the dying cpu, reenable alloc/free */
@@ -799,7 +814,7 @@ static void cpuhp_complete_idle_dead(voi
{
struct cpuhp_cpu_state *st = arg;

- complete(&st->done);
+ complete_ap_thread(st, false);
}

void cpuhp_report_idle_dead(void)
@@ -938,7 +953,7 @@ void cpuhp_online_idle(enum cpuhp_state
return;

st->state = CPUHP_AP_ONLINE_IDLE;
- complete(&st->done);
+ complete_ap_thread(st, true);
}

/* Requires cpu_add_remove_lock to be held */

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