linux-kernel - [patch 1/6] x86/smp: Remove pointless wmb() from native_stop_other

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Message-ID: <20230603200459.657036052@linutronix.de>
Date:   Sat,  3 Jun 2023 22:06:56 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     LKML <linux-kernel@...r.kernel.org>
Cc:     x86@...nel.org, Ashok Raj <ashok.raj@...ux.intel.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Tony Luck <tony.luck@...el.com>,
        Arjan van de Veen <arjan@...ux.intel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Eric Biederman <ebiederm@...ssion.com>
Subject: [patch 1/6] x86/smp: Remove pointless wmb() from native_stop_other_cpus()

The wmb() after the successfull atomic_cmpxchg() is complete voodoo along
with the comment stating "sync above data before sending IRQ".

There is no "above" data except for the atomic_t stopping_cpu which has
just been acquired. The reboot IPI handler does not check any data and
unconditionally disables the CPU.

Remove this cargo cult barrier.

Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
---
 arch/x86/kernel/smp.c |    3 ---
 1 file changed, 3 deletions(-)

--- a/arch/x86/kernel/smp.c
+++ b/arch/x86/kernel/smp.c
@@ -171,9 +171,6 @@ static void native_stop_other_cpus(int w
 		if (atomic_cmpxchg(&stopping_cpu, -1, safe_smp_processor_id()) != -1)
 			return;
 
-		/* sync above data before sending IRQ */
-		wmb();
-
 		apic_send_IPI_allbutself(REBOOT_VECTOR);
 
 		/*