[patch 14/37] cpu/hotplug: Rework sparse_irq locking in bringup_cpu()

Thomas Gleixner
2023-04-14T23:45:35Z

There is no harm to hold sparse_irq lock until the upcoming CPU completes
in cpuhp_online_idle(). This allows to remove cpu_online() synchronization
from architecture code.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
kernel/cpu.c | 28 +++++++++++++++++++---------
1 file changed, 19 insertions(+), 9 deletions(-)

--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -558,7 +558,7 @@ static int cpuhp_kick_ap(int cpu, struct
return ret;
}

-static int bringup_wait_for_ap(unsigned int cpu)
+static int bringup_wait_for_ap_online(unsigned int cpu)
{
struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, cpu);

@@ -579,15 +579,12 @@ static int bringup_wait_for_ap(unsigned
*/
if (!cpu_smt_allowed(cpu))
return -ECANCELED;
-
- if (st->target <= CPUHP_AP_ONLINE_IDLE)
- return 0;
-
- return cpuhp_kick_ap(cpu, st, st->target);
+ return 0;
}

static int bringup_cpu(unsigned int cpu)
{
+ struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, cpu);
struct task_struct *idle = idle_thread_get(cpu);
int ret;

@@ -606,10 +603,23 @@ static int bringup_cpu(unsigned int cpu)

/* Arch-specific enabling code. */
ret = __cpu_up(cpu, idle);
- irq_unlock_sparse();
if (ret)
- return ret;
- return bringup_wait_for_ap(cpu);
+ goto out_unlock;
+
+ ret = bringup_wait_for_ap_online(cpu);
+ if (ret)
+ goto out_unlock;
+
+ irq_unlock_sparse();
+
+ if (st->target <= CPUHP_AP_ONLINE_IDLE)
+ return 0;
+
+ return cpuhp_kick_ap(cpu, st, st->target);
+
+out_unlock:
+ irq_unlock_sparse();
+ return ret;
}

static int finish_cpu(unsigned int cpu)