From patchwork Tue Mar 7 14:35:57 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Valentin Schneider X-Patchwork-Id: 13163834 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id B333DC678D4 for ; Tue, 7 Mar 2023 14:48:26 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230079AbjCGOsZ (ORCPT ); Tue, 7 Mar 2023 09:48:25 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:54622 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230401AbjCGOqX (ORCPT ); Tue, 7 Mar 2023 09:46:23 -0500 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 605076A4C for ; Tue, 7 Mar 2023 06:37:57 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1678199829; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=QbSxuBYwyBhZhp7hgOeOy88U7e5YyI7vjVO9jj/5+zE=; b=YVQ5sIbU3PSHh9H92BNl/iDHZynMEgwfsBCy9pzUdt58quSiy+3guy5TBwn7tGJjJopAKJ 4quKa1pl5GUPU7PZKhWUwUpWrB+GQL/qglVLIC9S4mEZWl7rTNjWq9Se/F3CmADt82AMVv b8mNQUy92ztcNDKrhqLeFJujWqi7Q/M= Received: from mimecast-mx02.redhat.com (mx3-rdu2.redhat.com [66.187.233.73]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-435-w0wR9ByeM4e_eV67Jzxu2w-1; Tue, 07 Mar 2023 09:37:04 -0500 X-MC-Unique: w0wR9ByeM4e_eV67Jzxu2w-1 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.rdu2.redhat.com [10.11.54.1]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 9B173280AA28; Tue, 7 Mar 2023 14:37:02 +0000 (UTC) Received: from vschneid.remote.csb (unknown [10.33.37.13]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 8475A40AE20A; Tue, 7 Mar 2023 14:36:58 +0000 (UTC) From: Valentin Schneider To: linux-alpha@vger.kernel.org, linux-kernel@vger.kernel.org, linux-snps-arc@lists.infradead.org, linux-arm-kernel@lists.infradead.org, linux-csky@vger.kernel.org, linux-hexagon@vger.kernel.org, linux-ia64@vger.kernel.org, loongarch@lists.linux.dev, linux-mips@vger.kernel.org, openrisc@lists.librecores.org, linux-parisc@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-riscv@lists.infradead.org, linux-s390@vger.kernel.org, linux-sh@vger.kernel.org, sparclinux@vger.kernel.org, linux-xtensa@linux-xtensa.org, x86@kernel.org Cc: "Paul E. McKenney" , Steven Rostedt , Peter Zijlstra , Thomas Gleixner , Sebastian Andrzej Siewior , Juri Lelli , Daniel Bristot de Oliveira , Marcelo Tosatti , Frederic Weisbecker , Ingo Molnar , Borislav Petkov , Dave Hansen , "H. Peter Anvin" , Marc Zyngier , Mark Rutland , Russell King , Nicholas Piggin , Guo Ren , "David S. Miller" Subject: [PATCH v5 6/7] smp: reword smp call IPI comment Date: Tue, 7 Mar 2023 14:35:57 +0000 Message-Id: <20230307143558.294354-7-vschneid@redhat.com> In-Reply-To: <20230307143558.294354-1-vschneid@redhat.com> References: <20230307143558.294354-1-vschneid@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 3.1 on 10.11.54.1 Precedence: bulk List-ID: X-Mailing-List: linux-sh@vger.kernel.org Accessing the call_single_queue hasn't involved a spinlock since 2014: 6897fc22ea01 ("kernel: use lockless list for smp_call_function_single") The llist operations (namely cmpxchg() and xchg()) provide similar ordering guarantees, update the comment to lessen confusion. Signed-off-by: Valentin Schneider --- kernel/smp.c | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-) diff --git a/kernel/smp.c b/kernel/smp.c index 93b4386cd3096..821b5986721ac 100644 --- a/kernel/smp.c +++ b/kernel/smp.c @@ -495,9 +495,10 @@ void __smp_call_single_queue(int cpu, struct llist_node *node) #endif /* - * The list addition should be visible before sending the IPI - * handler locks the list to pull the entry off it because of - * normal cache coherency rules implied by spinlocks. + * The list addition should be visible to the target CPU when it pops + * the head of the list to pull the entry off it in the IPI handler + * because of normal cache coherency rules implied by the underlying + * llist ops. * * If IPIs can go out of order to the cache coherency protocol * in an architecture, sufficient synchronisation should be added