linux-kernel - [PATCH v2 1/2] x86/smp: Move the call to smp_processor

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Message-ID: <20231123203605.3474745-1-ubizjak@gmail.com>
Date:   Thu, 23 Nov 2023 21:34:22 +0100
From:   Uros Bizjak <ubizjak@...il.com>
To:     x86@...nel.org, linux-kernel@...r.kernel.org
Cc:     Uros Bizjak <ubizjak@...il.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>
Subject: [PATCH v2 1/2] x86/smp: Move the call to smp_processor_id() after the early exit

smp_processor_id() accesses the per-cpu variable, so the compiler
is not able to move the call after the early exit on its own.

Also rename "cpu" variable to a more descriptive "this_cpu".

No functional change intended.

Cc: Dave Hansen <dave.hansen@...ux.intel.com>
Cc: Andy Lutomirski <luto@...nel.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Ingo Molnar <mingo@...nel.org>
Cc: Borislav Petkov <bp@...en8.de>
Cc: "H. Peter Anvin" <hpa@...or.com>
Signed-off-by: Uros Bizjak <ubizjak@...il.com>
---
v2: Split from v1 patch.
---
 arch/x86/kernel/smp.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kernel/smp.c b/arch/x86/kernel/smp.c
index 96a771f9f930..97f6f0cbb43a 100644
--- a/arch/x86/kernel/smp.c
+++ b/arch/x86/kernel/smp.c
@@ -148,14 +148,15 @@ static int register_stop_handler(void)
 
 static void native_stop_other_cpus(int wait)
 {
-	unsigned int cpu = smp_processor_id();
+	unsigned int this_cpu;
 	unsigned long flags, timeout;
 
 	if (reboot_force)
 		return;
 
 	/* Only proceed if this is the first CPU to reach this code */
-	if (atomic_cmpxchg(&stopping_cpu, -1, cpu) != -1)
+	this_cpu = smp_processor_id();
+	if (atomic_cmpxchg(&stopping_cpu, -1, this_cpu) != -1)
 		return;
 
 	/* For kexec, ensure that offline CPUs are out of MWAIT and in HLT */
@@ -186,7 +187,7 @@ static void native_stop_other_cpus(int wait)
 	 * NMIs.
 	 */
 	cpumask_copy(&cpus_stop_mask, cpu_online_mask);
-	cpumask_clear_cpu(cpu, &cpus_stop_mask);
+	cpumask_clear_cpu(this_cpu, &cpus_stop_mask);
 
 	if (!cpumask_empty(&cpus_stop_mask)) {
 		apic_send_IPI_allbutself(REBOOT_VECTOR);
@@ -210,6 +211,8 @@ static void native_stop_other_cpus(int wait)
 		 * CPUs to stop.
 		 */
 		if (!smp_no_nmi_ipi && !register_stop_handler()) {
+			unsigned int cpu;
+
 			pr_emerg("Shutting down cpus with NMI\n");
 
 			for_each_cpu(cpu, &cpus_stop_mask)
-- 
2.42.0