Commit 22b612e2 authored by Thomas Gleixner's avatar Thomas Gleixner Committed by Peter Zijlstra
Browse files

cpu/hotplug: Rework sparse_irq locking in bringup_cpu() 



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: default avatarThomas Gleixner <tglx@linutronix.de>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Tested-by: default avatarMichael Kelley <mikelley@microsoft.com>
Tested-by: default avatarOleksandr Natalenko <oleksandr@natalenko.name>
Tested-by: Helge Deller <deller@gmx.de> # parisc
Tested-by: Guilherme G. Piccoli <gpiccoli@igalia.com> # Steam Deck
Link: https://lore.kernel.org/r/20230512205256.263722880@linutronix.de
parent c8b7fb09

kernel/cpu.c

+24 −10
Original line number Diff line number Diff line
@@ -558,7 +558,7 @@ static int cpuhp_kick_ap(int cpu, struct cpuhp_cpu_state *st, 
	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 int cpu) 
	 */

	if (!cpu_smt_allowed(cpu))

		return -ECANCELED;



	if (st->target <= CPUHP_AP_ONLINE_IDLE)

	return 0;



	return cpuhp_kick_ap(cpu, st, st->target);

}



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;
@@ -600,16 +597,33 @@ static int bringup_cpu(unsigned int cpu) 
	/*

	 * Some architectures have to walk the irq descriptors to

	 * setup the vector space for the cpu which comes online.

	 * Prevent irq alloc/free across the bringup.

	 *

	 * Prevent irq alloc/free across the bringup by acquiring the

	 * sparse irq lock. Hold it until the upcoming CPU completes the

	 * startup in cpuhp_online_idle() which allows to avoid

	 * intermediate synchronization points in the architecture code.

	 */

	irq_lock_sparse();



	/* Arch-specific enabling code. */

	ret = __cpu_up(cpu, idle);

	irq_unlock_sparse();

	if (ret)

		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;

	return bringup_wait_for_ap(cpu);

}



static int finish_cpu(unsigned int cpu)