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SubjectRe: [PATCH 5/7] smp/hotplug: Differentiate the AP completion between up and down
On Wed, Sep 20, 2017 at 07:00:19PM +0200, Peter Zijlstra wrote:
> 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.

Acked-by: Byungchul Park <byungchul.park@lge.com>

> 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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