[tip: smp/core] x86/smpboot: Remove wait for cpu_online()

[tip-bot2 for Thomas Gleixner]

The following commit has been merged into the smp/core branch of tip:

Commit-ID:     e464640cf7af12f3c2748065936b95eae1f735ba
Gitweb:        https://git.kernel.org/tip/e464640cf7af12f3c2748065936b95eae1f735ba
Author:        Thomas Gleixner <tglx@xxxxxxxxxxxxx>
AuthorDate:    Fri, 12 May 2023 23:07:22 +02:00
Committer:     Peter Zijlstra <peterz@xxxxxxxxxxxxx>
CommitterDate: Mon, 15 May 2023 13:44:54 +02:00

x86/smpboot: Remove wait for cpu_online()

Now that the core code drops sparse_irq_lock after the idle thread
synchronized, it's pointless to wait for the AP to mark itself online.

Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Tested-by: Michael Kelley <mikelley@xxxxxxxxxxxxx>
Tested-by: Oleksandr Natalenko <oleksandr@xxxxxxxxxxxxxx>
Tested-by: Helge Deller <deller@xxxxxx> # parisc
Tested-by: Guilherme G. Piccoli <gpiccoli@xxxxxxxxxx> # Steam Deck
Link: https://lore.kernel.org/r/20230512205256.316417181@xxxxxxxxxxxxx
---
 arch/x86/kernel/smpboot.c | 26 ++------------------------
 1 file changed, 2 insertions(+), 24 deletions(-)

diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
index 3f731be..4349e8a 100644
--- a/arch/x86/kernel/smpboot.c
+++ b/arch/x86/kernel/smpboot.c
@@ -275,7 +275,6 @@ static void notrace start_secondary(void *unused)
 	 * half valid vector space.
 	 */
 	lock_vector_lock();
-	/* Sync point with do_wait_cpu_online() */
 	set_cpu_online(smp_processor_id(), true);
 	lapic_online();
 	unlock_vector_lock();
@@ -1104,20 +1103,6 @@ static int wait_cpu_initialized(unsigned int cpu)
 	return 0;
 }
 
-/*
- * Bringup step three: Wait for the target AP to reach set_cpu_online() in
- * start_secondary().
- */
-static void wait_cpu_online(unsigned int cpu)
-{
-	/*
-	 * Wait for the AP to mark itself online, so the core caller
-	 * can drop sparse_irq_lock.
-	 */
-	while (!cpu_online(cpu))
-		schedule();
-}
-
 static int native_kick_ap(unsigned int cpu, struct task_struct *tidle)
 {
 	int apicid = apic->cpu_present_to_apicid(cpu);
@@ -1164,16 +1149,9 @@ int native_cpu_up(unsigned int cpu, struct task_struct *tidle)
 	int ret;
 
 	ret = native_kick_ap(cpu, tidle);
-	if (ret)
-		goto out;
-
-	ret = wait_cpu_initialized(cpu);
-	if (ret)
-		goto out;
-
-	wait_cpu_online(cpu);
+	if (!ret)
+		ret = wait_cpu_initialized(cpu);
 
-out:
 	/* Cleanup possible dangling ends... */
 	if (x86_platform.legacy.warm_reset)
 		smpboot_restore_warm_reset_vector();