linux-kernel - [tip: x86/core] x86/smp: Remove pointless wmb()s from native_stop_other

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Date:   Tue, 20 Jun 2023 13:00:51 -0000
From:   "tip-bot2 for Thomas Gleixner" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        "Borislav Petkov (AMD)" <bp@...en8.de>, stable@...r.kernel.org,
        x86@...nel.org, linux-kernel@...r.kernel.org
Subject: [tip: x86/core] x86/smp: Remove pointless wmb()s from
 native_stop_other_cpus()

The following commit has been merged into the x86/core branch of tip:

Commit-ID:     2affa6d6db28855e6340b060b809c23477aa546e
Gitweb:        https://git.kernel.org/tip/2affa6d6db28855e6340b060b809c23477aa546e
Author:        Thomas Gleixner <tglx@...utronix.de>
AuthorDate:    Thu, 15 Jun 2023 22:33:54 +02:00
Committer:     Thomas Gleixner <tglx@...utronix.de>
CommitterDate: Tue, 20 Jun 2023 14:51:46 +02:00

x86/smp: Remove pointless wmb()s from native_stop_other_cpus()

The wmb()s before sending the IPIs are not synchronizing anything.

If at all then the apic IPI functions have to provide or act as appropriate
barriers.

Remove these cargo cult barriers which have no explanation of what they are
synchronizing.

Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Reviewed-by: Borislav Petkov (AMD) <bp@...en8.de>
Cc: stable@...r.kernel.org
Link: https://lore.kernel.org/r/20230615193330.378358382@linutronix.de

---
 arch/x86/kernel/smp.c | 6 ------
 1 file changed, 6 deletions(-)

diff --git a/arch/x86/kernel/smp.c b/arch/x86/kernel/smp.c
index 935bc65..d842875 100644
--- a/arch/x86/kernel/smp.c
+++ b/arch/x86/kernel/smp.c
@@ -184,9 +184,6 @@ static void native_stop_other_cpus(int wait)
 	cpumask_clear_cpu(cpu, &cpus_stop_mask);
 
 	if (!cpumask_empty(&cpus_stop_mask)) {
-		/* sync above data before sending IRQ */
-		wmb();
-
 		apic_send_IPI_allbutself(REBOOT_VECTOR);
 
 		/*
@@ -208,9 +205,6 @@ static void native_stop_other_cpus(int wait)
 		 * CPUs to stop.
 		 */
 		if (!smp_no_nmi_ipi && !register_stop_handler()) {
-			/* Sync above data before sending IRQ */
-			wmb();
-
 			pr_emerg("Shutting down cpus with NMI\n");
 
 			for_each_cpu(cpu, &cpus_stop_mask)