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

commit 2affa6d upstream.

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@linutronix.de>
Reviewed-by: Borislav Petkov (AMD) <bp@alien8.de>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/20230615193330.378358382@linutronix.de
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

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)