This is a note to let you know that I've just added the patch titled
x86/smp: Remove pointless wmb()s from native_stop_other_cpus()
to the 6.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
x86-smp-remove-pointless-wmb-s-from-native_stop_other_cpus.patch
and it can be found in the queue-6.4 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 2affa6d6db28855e6340b060b809c23477aa546e Mon Sep 17 00:00:00 2001
From: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Date: Thu, 15 Jun 2023 22:33:54 +0200
Subject: x86/smp: Remove pointless wmb()s from native_stop_other_cpus()
From: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
commit 2affa6d6db28855e6340b060b809c23477aa546e 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@xxxxxxxxxxxxx>
Reviewed-by: Borislav Petkov (AMD) <bp@xxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Link: https://lore.kernel.org/r/20230615193330.378358382@xxxxxxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
arch/x86/kernel/smp.c | 6 ------
1 file changed, 6 deletions(-)
--- 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);
/*
@@ -208,9 +205,6 @@ static void native_stop_other_cpus(int w
* 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)
Patches currently in stable-queue which might be from tglx@xxxxxxxxxxxxx are
queue-6.4/x86-smp-cure-kexec-vs.-mwait_play_dead-breakage.patch
queue-6.4/x86-smp-remove-pointless-wmb-s-from-native_stop_other_cpus.patch
queue-6.4/x86-smp-dont-access-non-existing-cpuid-leaf.patch
queue-6.4/x86-smp-make-stop_other_cpus-more-robust.patch
queue-6.4/x86-smp-use-dedicated-cache-line-for-mwait_play_dead.patch
