diff mbox series

[v3,3/7] x86/smp: Remove pointless wmb()s from native_stop_other_cpus()

Message ID 20230615193330.378358382@linutronix.de
State New
Headers
Series x86/smp: Cure stop_other_cpus() and kexec() troubles |

Commit Message

Thomas Gleixner June 15, 2023, 8:33 p.m. UTC 
  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>
---
V3: Remove second instance and reword changelog - PeterZ
---
 arch/x86/kernel/smp.c |    6 ------
 1 file changed, 6 deletions(-)

Comments

Borislav Petkov June 20, 2023, 8:47 a.m. UTC | #1 
On Thu, Jun 15, 2023 at 10:33:54PM +0200, Thomas Gleixner wrote:
> 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>
> ---
> V3: Remove second instance and reword changelog - PeterZ
> ---
>  arch/x86/kernel/smp.c |    6 ------
>  1 file changed, 6 deletions(-)

Reviewed-by: Borislav Petkov (AMD) <bp@alien8.de>
diff mbox series

Patch

--- a/arch/x86/kernel/smp.c
+++ b/arch/x86/kernel/smp.c
@@ -184,9 +184,6 @@  static void native_stop_other_cpus(int w
 	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);
 
 		/*
@@ -210,9 +207,6 @@  static void native_stop_other_cpus(int w
 		if (!smp_no_nmi_ipi && !register_stop_handler()) {
 			u32 dm;
 
-			/* Sync above data before sending IRQ */
-			wmb();
-
 			pr_emerg("Shutting down cpus with NMI\n");
 
 			dm = apic->dest_mode_logical ? APIC_DEST_LOGICAL : APIC_DEST_PHYSICAL;