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=-8.5 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,T_DKIMWL_WL_HIGH,USER_AGENT_MUTT 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 E119EC28CC0 for ; Thu, 30 May 2019 12:01:45 +0000 (UTC) Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 95D44258AB for ; Thu, 30 May 2019 12:01:45 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="h2HfNMVq" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 95D44258AB Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20170209; h=Sender: Content-Transfer-Encoding:Content-Type:Cc:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References: Message-ID:Subject:To:From:Date:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=XosMt4rWYSzxLsx1o2C3XDns2OrFvXojzKyrFuUAF2o=; b=h2HfNMVq8X9TxN KRktwXv421XJFVeEmCL6zr4edrfe3dI2pvfQYkcP1Fp48Lq+bk8etWL72+kz4U9Lsc++0geFMNhIX cg/K0ShIv1r1KSex0vvpyrwE4Kmz9a7Bqmrx3vKxUxx+BvKYEbEJ506xIDQqNVyaaJ7DFjFkwf99w WgNx6AwLeS96MrCc+3d8hRX5JNrsxhixHdcIhGKvsFsRheiMrpbwF7pYmm9UUPR+zra+jqAnBOZD9 /saftE8l1BomaOaaK2RUtJkcP1r51ObysaaxUem1K/a9VZ/bqk4b8GM1EwHaajvMCyCQDPzsQs2E6 QiMT2CoFiRDpJFQHE+1Q==; Received: from localhost ([127.0.0.1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.90_1 #2 (Red Hat Linux)) id 1hWJkZ-0001PC-4l; Thu, 30 May 2019 12:01:39 +0000 Received: from foss.arm.com ([217.140.101.70]) by bombadil.infradead.org with esmtp (Exim 4.90_1 #2 (Red Hat Linux)) id 1hWJkW-0001M0-ED for linux-arm-kernel@lists.infradead.org; Thu, 30 May 2019 12:01:37 +0000 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.72.51.249]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id E2154374; Thu, 30 May 2019 05:01:33 -0700 (PDT) Received: from fuggles.cambridge.arm.com (usa-sjc-imap-foss1.foss.arm.com [10.72.51.249]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 2086D3F5AF; Thu, 30 May 2019 05:01:31 -0700 (PDT) Date: Thu, 30 May 2019 13:01:29 +0100 From: Will Deacon To: Julien Grall Subject: Re: [PATCH] arm64/cpufeature: Convert hook_lock to raw_spin_lock_t in cpu_enable_ssbs() Message-ID: <20190530120129.GD13751@fuggles.cambridge.arm.com> References: <20190530113058.1988-1-julien.grall@arm.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20190530113058.1988-1-julien.grall@arm.com> User-Agent: Mutt/1.11.1+86 (6f28e57d73f2) () X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20190530_050136_483006_896826DC X-CRM114-Status: GOOD ( 21.92 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: linux-rt-users@vger.kernel.org, suzuki.poulose@arm.com, catalin.marinas@arm.com, bigeasy@linutronix.de, linux-kernel@vger.kernel.org, rostedt@goodmis.org, tglx@linutronix.de, dave.martin@arm.com, linux-arm-kernel@lists.infradead.org Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Thu, May 30, 2019 at 12:30:58PM +0100, Julien Grall wrote: > cpu_enable_ssbs() is called via stop_machine() as part of the cpu_enable > callback. A spin lock is used to ensure the hook is registered before > the rest of the callback is executed. > > On -RT spin_lock() may sleep. However, all the callees in stop_machine() > are expected to not sleep. Therefore a raw_spin_lock() is required here. > > Given this is already done under stop_machine() and the work done under > the lock is quite small, the latency should not increase too much. > > Signed-off-by: Julien Grall > > --- > > It was noticed when looking at the current use of spin_lock in > arch/arm64. I don't have a platform calling that callback, so I have > hacked the code to reproduce the error and check it is now fixed. > --- > arch/arm64/kernel/cpufeature.c | 6 +++--- > 1 file changed, 3 insertions(+), 3 deletions(-) > > diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c > index ca27e08e3d8a..2a7159fda3ce 100644 > --- a/arch/arm64/kernel/cpufeature.c > +++ b/arch/arm64/kernel/cpufeature.c > @@ -1194,14 +1194,14 @@ static struct undef_hook ssbs_emulation_hook = { > static void cpu_enable_ssbs(const struct arm64_cpu_capabilities *__unused) > { > static bool undef_hook_registered = false; > - static DEFINE_SPINLOCK(hook_lock); > + static DEFINE_RAW_SPINLOCK(hook_lock); > > - spin_lock(&hook_lock); > + raw_spin_lock(&hook_lock); > if (!undef_hook_registered) { > register_undef_hook(&ssbs_emulation_hook); > undef_hook_registered = true; > } > - spin_unlock(&hook_lock); > + raw_spin_unlock(&hook_lock); Makes sense to me. We could probably avoid the lock entirely if we wanted to (via atomic_dec_if_positive), but I'm not sure it's really worth it. Will _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel