From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-3.9 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,URIBL_BLOCKED autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 4E5E9C65BAF for ; Sun, 9 Dec 2018 22:07:58 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 1F03820661 for ; Sun, 9 Dec 2018 22:07:58 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 1F03820661 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=decadent.org.uk Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727959AbeLIWH5 (ORCPT ); Sun, 9 Dec 2018 17:07:57 -0500 Received: from shadbolt.e.decadent.org.uk ([88.96.1.126]:37272 "EHLO shadbolt.e.decadent.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727945AbeLIWHy (ORCPT ); Sun, 9 Dec 2018 17:07:54 -0500 Received: from pub.yeoldevic.com ([81.174.156.145] helo=deadeye) by shadbolt.decadent.org.uk with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.89) (envelope-from ) id 1gW73O-0002io-HI; Sun, 09 Dec 2018 21:55:58 +0000 Received: from ben by deadeye with local (Exim 4.91) (envelope-from ) id 1gW72Z-0003G2-Q2; Sun, 09 Dec 2018 21:55:07 +0000 Content-Type: text/plain; charset="UTF-8" Content-Disposition: inline Content-Transfer-Encoding: 8bit MIME-Version: 1.0 From: Ben Hutchings To: linux-kernel@vger.kernel.org, stable@vger.kernel.org CC: akpm@linux-foundation.org, "Zhangjin Wu" , "James Hogan" , linux-mips@linux-mips.org, "Huacai Chen" , "Ralf Baechle" , "Fuxin Zhang" , "Paul Burton" , "Huacai Chen" Date: Sun, 09 Dec 2018 21:50:33 +0000 Message-ID: X-Mailer: LinuxStableQueue (scripts by bwh) X-Patchwork-Hint: ignore Subject: [PATCH 3.16 049/328] MIPS: Change definition of cpu_relax() for Loongson-3 In-Reply-To: X-SA-Exim-Connect-IP: 81.174.156.145 X-SA-Exim-Mail-From: ben@decadent.org.uk X-SA-Exim-Scanned: No (on shadbolt.decadent.org.uk); SAEximRunCond expanded to false Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 3.16.62-rc1 review patch. If anyone has any objections, please let me know. ------------------ From: Huacai Chen commit a30718868915fbb991a9ae9e45594b059f28e9ae upstream. Linux expects that if a CPU modifies a memory location, then that modification will eventually become visible to other CPUs in the system. Loongson 3 CPUs include a Store Fill Buffer (SFB) which sits between a core & its L1 data cache, queueing memory accesses & allowing for faster forwarding of data from pending stores to younger loads from the core. Unfortunately the SFB prioritizes loads such that a continuous stream of loads may cause a pending write to be buffered indefinitely. This is problematic if we end up with 2 CPUs which each perform a store that the other polls for - one or both CPUs may end up with their stores buffered in the SFB, never reaching cache due to the continuous reads from the poll loop. Such a deadlock condition has been observed whilst running qspinlock code. This patch changes the definition of cpu_relax() to smp_mb() for Loongson-3, forcing a flush of the SFB on SMP systems which will cause any pending writes to make it as far as the L1 caches where they will become visible to other CPUs. If the kernel is not compiled for SMP support, this will expand to a barrier() as before. This workaround matches that currently implemented for ARM when CONFIG_ARM_ERRATA_754327=y, which was introduced by commit 534be1d5a2da ("ARM: 6194/1: change definition of cpu_relax() for ARM11MPCore"). Although the workaround is only required when the Loongson 3 SFB functionality is enabled, and we only began explicitly enabling that functionality in v4.7 with commit 1e820da3c9af ("MIPS: Loongson-3: Introduce CONFIG_LOONGSON3_ENHANCEMENT"), existing or future firmware may enable the SFB which means we may need the workaround backported to earlier kernels too. [paul.burton@mips.com: - Reword commit message & comment. - Limit stable backport to v3.15+ where we support Loongson 3 CPUs.] Signed-off-by: Huacai Chen Signed-off-by: Paul Burton References: 534be1d5a2da ("ARM: 6194/1: change definition of cpu_relax() for ARM11MPCore") References: 1e820da3c9af ("MIPS: Loongson-3: Introduce CONFIG_LOONGSON3_ENHANCEMENT") Patchwork: https://patchwork.linux-mips.org/patch/19830/ Cc: Ralf Baechle Cc: James Hogan Cc: linux-mips@linux-mips.org Cc: Fuxin Zhang Cc: Zhangjin Wu Cc: Huacai Chen Signed-off-by: Ben Hutchings --- arch/mips/include/asm/processor.h | 13 +++++++++++++ 1 file changed, 13 insertions(+) --- a/arch/mips/include/asm/processor.h +++ b/arch/mips/include/asm/processor.h @@ -366,7 +366,20 @@ unsigned long get_wchan(struct task_stru #define KSTK_ESP(tsk) (task_pt_regs(tsk)->regs[29]) #define KSTK_STATUS(tsk) (task_pt_regs(tsk)->cp0_status) +#ifdef CONFIG_CPU_LOONGSON3 +/* + * Loongson-3's SFB (Store-Fill-Buffer) may buffer writes indefinitely when a + * tight read loop is executed, because reads take priority over writes & the + * hardware (incorrectly) doesn't ensure that writes will eventually occur. + * + * Since spin loops of any kind should have a cpu_relax() in them, force an SFB + * flush from cpu_relax() such that any pending writes will become visible as + * expected. + */ +#define cpu_relax() smp_mb() +#else #define cpu_relax() barrier() +#endif /* * Return_address is a replacement for __builtin_return_address(count)