From mboxrd@z Thu Jan 1 00:00:00 1970 From: Valentin Schneider 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> References: <20230307143558.294354-1-vschneid@redhat.com> Mime-Version: 1.0 Content-Transfer-Encoding: 8bit Return-path: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1678199830; 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=Kw08rRxhplwQ4DRP2ZOCGNYIP13/oA0anvKsYsfpVb4QOzF3coiwHDPJo5wx5GxFLimDG6 p92jUKRpMKu8b3SQCqjh1WIKWSTCBxFH7MKWIC/eeh16a/fnhCNp4aJxNeUqfXH/r9XVhj /fyunbEszAicopjPBVlsRSiSovi+cSE= DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1678199830; 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=Kw08rRxhplwQ4DRP2ZOCGNYIP13/oA0anvKsYsfpVb4QOzF3coiwHDPJo5wx5GxFLimDG6 p92jUKRpMKu8b3SQCqjh1WIKWSTCBxFH7MKWIC/eeh16a/fnhCNp4aJxNeUqfXH/r9XVhj /fyunbEszAicopjPBVlsRSiSovi+cSE= In-Reply-To: <20230307143558.294354-1-vschneid@redhat.com> List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: linuxppc-dev-bounces+glppe-linuxppc-embedded-2=m.gmane-mx.org@lists.ozlabs.org Sender: "Linuxppc-dev" Content-Type: text/plain; charset="us-ascii" 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: Juri Lelli , Mark Rutland , Dave Hansen , "Paul E. McKenney" , Peter Zijlstra , Marc Zyngier , Sebastian Andrzej Siewior , Marcelo Tosatti , Russell King , Steven Rostedt , "David S. Miller" , Ingo Molnar , Borislav Petkov , Nicholas Piggin , "H. Peter Anvin" , Guo Ren , Thomas Gleixner , Daniel Bristot de Oliveira , Frederic Weisbecker 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 -- 2.31.1