linux-kernel - [GIT PULL] locking fix

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Message-ID: <aQ8_0mAj3AUGgguL@gmail.com>
Date: Sat, 8 Nov 2025 14:04:18 +0100
From: Ingo Molnar <mingo@...nel.org>
To: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: linux-kernel@...r.kernel.org, Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Will Deacon <will@...nel.org>, Thomas Gleixner <tglx@...utronix.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Boqun Feng <boqun.feng@...il.com>, Waiman Long <longman@...hat.com>,
	Borislav Petkov <bp@...en8.de>
Subject: [GIT PULL] locking fix

Linus,

Please pull the latest locking/urgent Git tree from:

   git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git locking-urgent-2025-11-08

   # HEAD: 4cb5ac2626b5704ed712ac1d46b9d89fdfc12c5d futex: Optimize per-cpu reference counting

Fix (well, cut in half) a futex performance regression on PowerPC.

 Thanks,

	Ingo

------------------>
Peter Zijlstra (1):
      futex: Optimize per-cpu reference counting


 kernel/futex/core.c | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/kernel/futex/core.c b/kernel/futex/core.c
index 125804fbb5cb..2e77a6e5c865 100644
--- a/kernel/futex/core.c
+++ b/kernel/futex/core.c
@@ -1680,10 +1680,10 @@ static bool futex_ref_get(struct futex_private_hash *fph)
 {
 	struct mm_struct *mm = fph->mm;
 
-	guard(rcu)();
+	guard(preempt)();
 
-	if (smp_load_acquire(&fph->state) == FR_PERCPU) {
-		this_cpu_inc(*mm->futex_ref);
+	if (READ_ONCE(fph->state) == FR_PERCPU) {
+		__this_cpu_inc(*mm->futex_ref);
 		return true;
 	}
 
@@ -1694,10 +1694,10 @@ static bool futex_ref_put(struct futex_private_hash *fph)
 {
 	struct mm_struct *mm = fph->mm;
 
-	guard(rcu)();
+	guard(preempt)();
 
-	if (smp_load_acquire(&fph->state) == FR_PERCPU) {
-		this_cpu_dec(*mm->futex_ref);
+	if (READ_ONCE(fph->state) == FR_PERCPU) {
+		__this_cpu_dec(*mm->futex_ref);
 		return false;
 	}