[PATCH v2 02/23] cpu/hotplug: Avoid trying to bring up CPUs that are already online

[Will Deacon <will@kernel.org>]

There's little point trying to bring up a CPU that is already online.
Although _cpu_up() handles this case by doing nothing (because the
target state has already been reached), it's wasted effort when we can
easily elide the call to cpu_up() in the first place.

Check that the target CPU isn't already online before invoking cpu_up()
from cpuhp_bringup_mask().

Reviewed-by: Jinjie Ruan <ruanjinjie@huawei.com>
Signed-off-by: Will Deacon <will@kernel.org>
---
 kernel/cpu.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/kernel/cpu.c b/kernel/cpu.c
index 198c929c452a..97a9bfe4edad 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -1769,7 +1769,8 @@ static void __init cpuhp_bringup_mask(const struct cpumask *mask, unsigned int n
 	for_each_cpu(cpu, mask) {
 		struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, cpu);
 
-		if (cpu_up(cpu, target) && can_rollback_cpu(st)) {
+		if (!cpu_online(cpu) && cpu_up(cpu, target) &&
+		    can_rollback_cpu(st)) {
 			/*
 			 * If this failed then cpu_up() might have only
 			 * rolled back to CPUHP_BP_KICK_AP for the final
-- 
2.56.0.385.gd3acb90ef8-goog