linux-kernel - [RFC] cpu/hotplug: allow the cpu in UP

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Date:   Wed, 1 Sep 2021 13:11:43 +0800
From:   "Longpeng(Mike)" <longpeng2@...wei.com>
To:     <peterz@...radead.org>, <valentin.schneider@....com>,
        <mingo@...nel.org>, <tglx@...utronix.de>, <bigeasy@...utronix.de>
CC:     <linux-kernel@...r.kernel.org>, <arei.gonglei@...wei.com>,
        "Longpeng(Mike)" <longpeng2@...wei.com>
Subject: [RFC] cpu/hotplug: allow the cpu in UP_PREPARE state to bringup again

The cpu's cpu_hotplug_state will be set to CPU_UP_PREPARE before
the cpu is waken up, but it won't be reset when the failure occurs.
Then the user cannot to make the cpu online anymore, because the
CPU_UP_PREPARE state makes cpu_check_up_prepare() unhappy.

We should allow the user to try again in this case.

Signed-off-by: Longpeng(Mike) <longpeng2@...wei.com>
---
 kernel/smpboot.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/kernel/smpboot.c b/kernel/smpboot.c
index f6bc0bc..d18f8ff 100644
--- a/kernel/smpboot.c
+++ b/kernel/smpboot.c
@@ -392,6 +392,13 @@ int cpu_check_up_prepare(int cpu)
 		 */
 		return -EAGAIN;
 
+	case CPU_UP_PREPARE:
+		/*
+		 * The CPU failed to bringup last time, allow the user
+		 * continue to try to start it up.
+		 */
+		return 0;
+
 	default:
 
 		/* Should not happen.  Famous last words. */
-- 
1.8.3.1