From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-wr1-f46.google.com (mail-wr1-f46.google.com [209.85.221.46]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id CAEE535F605 for ; Fri, 6 Mar 2026 22:51:58 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.221.46 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772837520; cv=none; b=B2+Ph9xZumW1fFPfKGT0zRUqnR6A4/nJWrgY1rBH+jGuP0LILKno+cnc8K1CGf5kKJDJRToIRe61aXG3JE6kcXFyaqbIfCRxr7Y7+OXMnxIVpBxMQYQjna0rC4787FGn3Qo3tN0DLNSt+vK9/Crw02d5YP++gqnUTZRrODXIHVk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772837520; c=relaxed/simple; bh=DJS65YAxdEKgmmrRmE62iYKU6tqUYfBx7qz154siKGk=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version; b=qSLnzHEsCmFhP356S+RcS/Tt70uEp8V/S333zcra7gZfnaApf8MSlCs4nuQ0xMdhjVK7gtUpmWdGcyP0VloPaOGiNaJCZRJID4WUvpb3HI6gQ6Ci9iW2Ity2XaW1QbQcuvoPHU0castji8q75UczNyc1Wxp9f2nGVznvH1ZTBps= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com; spf=pass smtp.mailfrom=gmail.com; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b=KLhn57eN; arc=none smtp.client-ip=209.85.221.46 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=gmail.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="KLhn57eN" Received: by mail-wr1-f46.google.com with SMTP id ffacd0b85a97d-439aeed8a5bso6843762f8f.3 for ; Fri, 06 Mar 2026 14:51:58 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20230601; t=1772837517; x=1773442317; darn=vger.kernel.org; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:from:to:cc:subject:date :message-id:reply-to; bh=Vz6EDb2VJ3SyH7oyHxjL4QyEQVmIWY9QfoNC0OG/wKw=; b=KLhn57eNn6j3z/IX9BaNLB3LfBxR/kyac88PAoZ57Pq9ehKJmxXpQewtdtSe55Q5WC mJnoziIhNV+LBb/ZYsdlsCkPI/MIW51YS6M/73LjwVXBx66GeiSufBpH/FcweQWMtlIx sctQynb560UjlYz4SU6+LUijmPMi+bu+WpZ5cGh6JVjVAtWtlXPmWYK6iCFovp4jZl4G KIVEavtnz5pbPVT5o9lozV95Bi2j27PleEJf9f2OmVR2ZzLo5I6gwTAjbZHislkaSHv8 CUyf/uMVAd3S+/dIPkpif0huTQkpGCsBH6FnDCZtAtFLyvR6yA6+lM4x/9X65uJjHVwU TazA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1772837517; x=1773442317; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:x-gm-gg:x-gm-message-state:from :to:cc:subject:date:message-id:reply-to; bh=Vz6EDb2VJ3SyH7oyHxjL4QyEQVmIWY9QfoNC0OG/wKw=; b=WqZJgVWFolGisDUeBToE5NfKBtYR0UvNK5K0UHif0QUnGOGgqZ4uuLfmEY6lk1ANFf mhMRmOQ1ov3VCzF8IdFw0355bU5Zm1LIK2rCnKbNJITq3SIDHbHFTNPqcvRmJjws2dqa +WZhP/ie91Eu86KF7BvMBfLZoiRNvJktxOM5+UawtYCSNNnwIpsplISkEPCBiBbxPvm1 byJsB1L6Rk/onb5w8NHokjIF9olYDYpqARgktBOaajlGBPpz6pPD+bT20nLu3vRBnlBH CnNNXXNgsmdUPxHGcNCQTh0MgU9a8kvwMrWl6Y3JFxH8znVgFDKarE8e2DZMySGzAOpK dMSQ== X-Forwarded-Encrypted: i=1; AJvYcCW3i/vXbjeu+q+MmIcKTHRpRAdB2TfCpJowPA5vJLuOBNjI5syug4YFLujZX+CI/FvJMrRbb2lPh6UPlY0=@vger.kernel.org X-Gm-Message-State: AOJu0YxZyet/rDhxBvAUIYyKWZVwMwZKlyhg4dKwMJg+6GFT5RBZ0Ut1 kIl+4VL6qwCOx0nsBuRbW6XXcEJkcb79IRfTLLXpwGD2BslGry2sg1G1yDEYJzBN X-Gm-Gg: ATEYQzxzwi30wRbfXxq0yDzkuV1nZJ0sePd28aP7kIfpTW7SdhIHMfAcvO9WJM3hDc+ WnLrxMCIxpQoPFty4/TBRSklK5eReW0gzmtWhxu2SDbt3zeF85Q5iYaeBK+YC6GMJR/9PWPwZpG lQL8d2zv870ySwESUcOfYj5wEBn2/Fm81CDAMspxit983X6M+e5+YToaHnj+r4vKS95M0iIFXoW cWhqkfDqfu8hd3o0ZKhDV0HPmeQjjwqxHtzUOZC4WeVT750x+RaBJaDcTI8vf4QIleR3VZzEBn8 xgWWHBkRQTo4767TKx5mycvmL2Amrb7YnxU+1b7XxokTKnx5nbeLU/or+Os7b3vh9poSt/QKN9C DrKpfIzsWOc8Y6TxzJxvQJ+HpH9ED0SfUmwbBPTRA+QsSfFCAVE71I13WeEvlXiZh1qlyHCgZD6 25vw0ijkhBZFOHs6IEQy0elSPgyiNKkIdArNhmLp5dMHPAp599aK6CRRd2pVCgSZdVhaOKFMmbb wGy+hVzsVDX X-Received: by 2002:a05:6000:290d:b0:439:b6ae:5d5f with SMTP id ffacd0b85a97d-439da882118mr6888653f8f.36.1772837517173; Fri, 06 Mar 2026 14:51:57 -0800 (PST) Received: from snowdrop.snailnet.com (82-69-66-36.dsl.in-addr.zen.co.uk. [82.69.66.36]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-439dae57c05sm6160845f8f.39.2026.03.06.14.51.56 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 06 Mar 2026 14:51:56 -0800 (PST) From: david.laight.linux@gmail.com To: Waiman Long , Peter Zijlstra , Ingo Molnar , Will Deacon , Boqun Feng , linux-kernel@vger.kernel.org, Linus Torvalds , Yafang Shao , Steven Rostedt Cc: David Laight Subject: [PATCH v3 next 5/5] Avoid writing to node->next in the osq_lock() fast path Date: Fri, 6 Mar 2026 22:51:50 +0000 Message-Id: <20260306225150.93178-6-david.laight.linux@gmail.com> X-Mailer: git-send-email 2.39.5 In-Reply-To: <20260306225150.93178-1-david.laight.linux@gmail.com> References: <20260306225150.93178-1-david.laight.linux@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: David Laight When osq_lock() returns false or osq_unlock() returns static analysis shows that node->next should always be NULL. This means that it isn't necessary to explicitly set it to NULL prior to atomic_xchg(&lock->tail, curr) on entry to osq_lock(). Defer determining the address of the CPU's 'node' until after the atomic_exchange() so that it isn't done in the uncontented path. Signed-off-by: David Laight --- kernel/locking/osq_lock.c | 6 ++---- 1 file changed, 2 insertions(+), 4 deletions(-) diff --git a/kernel/locking/osq_lock.c b/kernel/locking/osq_lock.c index 0619691e2756..3f0cfdf1cd0f 100644 --- a/kernel/locking/osq_lock.c +++ b/kernel/locking/osq_lock.c @@ -92,13 +92,10 @@ osq_wait_next(struct optimistic_spin_queue *lock, bool osq_lock(struct optimistic_spin_queue *lock) { - struct optimistic_spin_node *node = this_cpu_ptr(&osq_node); - struct optimistic_spin_node *prev, *next; + struct optimistic_spin_node *node, *prev, *next; unsigned int curr = encode_cpu(smp_processor_id()); unsigned int prev_cpu; - node->next = NULL; - /* * We need both ACQUIRE (pairs with corresponding RELEASE in * unlock() uncontended, or fastpath) and RELEASE (to publish @@ -109,6 +106,7 @@ bool osq_lock(struct optimistic_spin_queue *lock) if (prev_cpu == OSQ_UNLOCKED_VAL) return true; + node = this_cpu_ptr(&osq_node); WRITE_ONCE(node->prev_cpu, prev_cpu); prev = decode_cpu(prev_cpu); node->locked = 0; -- 2.39.5