linux-kernel - [PATCH arm] Use common outgoing-CPU-notification code

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Message-Id: <20190611192410.GA27930@linux.ibm.com>
Date:   Tue, 11 Jun 2019 12:24:10 -0700
From:   "Paul E. McKenney" <paulmck@...ux.ibm.com>
To:     linux@....linux.org.uk, mark.rutland@....com,
        dietmar.eggemann@....com
Cc:     linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: [PATCH arm] Use common outgoing-CPU-notification code

This commit removes the open-coded CPU-offline notification with new
common code.  In particular, this change avoids calling scheduler code
using RCU from an offline CPU that RCU is ignoring.  This is a minimal
change.  A more intrusive change might invoke the cpu_check_up_prepare()
and cpu_set_state_online() functions at CPU-online time, which would
allow onlining throw an error if the CPU did not go offline properly.

Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
Cc: linux-arm-kernel@...ts.infradead.org
Cc: Russell King <linux@....linux.org.uk>
Cc: Mark Rutland <mark.rutland@....com>
Tested-by: Dietmar Eggemann <dietmar.eggemann@....com>

diff --git a/arch/arm/kernel/smp.c b/arch/arm/kernel/smp.c
index ebc53804d57b..8687d619260f 100644
--- a/arch/arm/kernel/smp.c
+++ b/arch/arm/kernel/smp.c
@@ -267,15 +267,13 @@ int __cpu_disable(void)
 	return 0;
 }

-static DECLARE_COMPLETION(cpu_died);
-
 /*
  * called on the thread which is asking for a CPU to be shutdown -
  * waits until shutdown has completed, or it is timed out.
  */
 void __cpu_die(unsigned int cpu)
 {
-	if (!wait_for_completion_timeout(&cpu_died, msecs_to_jiffies(5000))) {
+	if (!cpu_wait_death(cpu, 5)) {
 		pr_err("CPU%u: cpu didn't die\n", cpu);
 		return;
 	}
@@ -322,7 +320,7 @@ void arch_cpu_idle_dead(void)
 	 * this returns, power and/or clocks can be removed at any point
 	 * from this CPU and its cache by platform_cpu_kill().
 	 */
-	complete(&cpu_died);
+	(void)cpu_report_death();

 	/*
 	 * Ensure that the cache lines associated with that completion are