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=-8.3 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 779B8C43331 for ; Fri, 27 Mar 2020 06:50:29 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 475B520578 for ; Fri, 27 Mar 2020 06:50:29 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=c-s.fr header.i=@c-s.fr header.b="pDvSIsk8" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726360AbgC0Gu2 (ORCPT ); Fri, 27 Mar 2020 02:50:28 -0400 Received: from pegase1.c-s.fr ([93.17.236.30]:5854 "EHLO pegase1.c-s.fr" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725992AbgC0Gu1 (ORCPT ); Fri, 27 Mar 2020 02:50:27 -0400 Received: from localhost (mailhub1-int [192.168.12.234]) by localhost (Postfix) with ESMTP id 48pXYF0HKqz9txpx; Fri, 27 Mar 2020 07:50:25 +0100 (CET) Authentication-Results: localhost; dkim=pass reason="1024-bit key; insecure key" header.d=c-s.fr header.i=@c-s.fr header.b=pDvSIsk8; dkim-adsp=pass; dkim-atps=neutral X-Virus-Scanned: Debian amavisd-new at c-s.fr Received: from pegase1.c-s.fr ([192.168.12.234]) by localhost (pegase1.c-s.fr [192.168.12.234]) (amavisd-new, port 10024) with ESMTP id 9c3JvdN5GUEC; Fri, 27 Mar 2020 07:50:24 +0100 (CET) Received: from messagerie.si.c-s.fr (messagerie.si.c-s.fr [192.168.25.192]) by pegase1.c-s.fr (Postfix) with ESMTP id 48pXYD6KQRz9txpw; Fri, 27 Mar 2020 07:50:24 +0100 (CET) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=c-s.fr; s=mail; t=1585291824; bh=hAABVY6NqVGKI9aIL19sjFZK5w87U11qF1N1xyDIMOU=; h=Subject:To:Cc:References:From:Date:In-Reply-To:From; b=pDvSIsk8b/wsU/W/xdQHaHU3X4yZMJUw38gYA4+Vv5rXQaJIFGpiAVlSoCpFhxtcW 3wqHC/fNrVURiU1MrDudrICkh4dbRM085tn5JZ51PA3UPb06TMzFCJt84BAPL8nM8t C+u5t5Rwl8Z+4I7bPftzFeS/HLzjjTjKn6xvG/m4= Received: from localhost (localhost [127.0.0.1]) by messagerie.si.c-s.fr (Postfix) with ESMTP id B503C8B7BC; Fri, 27 Mar 2020 07:50:25 +0100 (CET) X-Virus-Scanned: amavisd-new at c-s.fr Received: from messagerie.si.c-s.fr ([127.0.0.1]) by localhost (messagerie.si.c-s.fr [127.0.0.1]) (amavisd-new, port 10023) with ESMTP id KttQcZwNJpxx; Fri, 27 Mar 2020 07:50:25 +0100 (CET) Received: from [192.168.4.90] (unknown [192.168.4.90]) by messagerie.si.c-s.fr (Postfix) with ESMTP id EA0608B756; Fri, 27 Mar 2020 07:50:24 +0100 (CET) Subject: Re: [PATCH 1/1] ppc/crash: Skip spinlocks during crash To: Leonardo Bras , Peter Zijlstra , Ingo Molnar , Will Deacon , Benjamin Herrenschmidt , Paul Mackerras , Michael Ellerman , Enrico Weigelt , Allison Randal , Thomas Gleixner Cc: linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org References: <20200326222836.501404-1-leonardo@linux.ibm.com> From: Christophe Leroy Message-ID: Date: Fri, 27 Mar 2020 07:50:20 +0100 User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:68.0) Gecko/20100101 Thunderbird/68.6.0 MIME-Version: 1.0 In-Reply-To: <20200326222836.501404-1-leonardo@linux.ibm.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: fr Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Le 26/03/2020 à 23:28, Leonardo Bras a écrit : > During a crash, there is chance that the cpus that handle the NMI IPI > are holding a spin_lock. If this spin_lock is needed by crashing_cpu it > will cause a deadlock. (rtas_lock and printk logbuf_log as of today) > > This is a problem if the system has kdump set up, given if it crashes > for any reason kdump may not be saved for crash analysis. > > Skip spinlocks after NMI IPI is sent to all other cpus. > > Signed-off-by: Leonardo Bras > --- > arch/powerpc/include/asm/spinlock.h | 6 ++++++ > arch/powerpc/kexec/crash.c | 3 +++ > 2 files changed, 9 insertions(+) > > diff --git a/arch/powerpc/include/asm/spinlock.h b/arch/powerpc/include/asm/spinlock.h > index 860228e917dc..a6381d110795 100644 > --- a/arch/powerpc/include/asm/spinlock.h > +++ b/arch/powerpc/include/asm/spinlock.h > @@ -111,6 +111,8 @@ static inline void splpar_spin_yield(arch_spinlock_t *lock) {}; > static inline void splpar_rw_yield(arch_rwlock_t *lock) {}; > #endif > > +extern bool crash_skip_spinlock __read_mostly; > + > static inline bool is_shared_processor(void) > { > #ifdef CONFIG_PPC_SPLPAR > @@ -142,6 +144,8 @@ static inline void arch_spin_lock(arch_spinlock_t *lock) > if (likely(__arch_spin_trylock(lock) == 0)) > break; > do { > + if (unlikely(crash_skip_spinlock)) > + return; You are adding a test that reads a global var in the middle of a so hot path ? That must kill performance. Can we do different ? Christophe