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=-8.2 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=unavailable 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 382E7C76195 for ; Thu, 18 Jul 2019 09:20:39 +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 0E3D52173B for ; Thu, 18 Jul 2019 09:20:39 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="h4sIK12J" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 0E3D52173B 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=hcnASE+Myqww2IOsOjrdZiYjAevPWw1oGKSpOtVsZRg=; b=h4sIK12JDVol7e z9pfRlGH+28+FJ2DeYM+B7q2a1TAPp60eEnWpvku4XLGeokPc2uqiZ0dtZtNY3cboi24Gpy0X+D7k tVnR/6wHDRcCU//P/K/5VgcZ7f4pjoS70WjdVJ0eG9ejafmoCf7UIm9shaaTAxsUccSlgW64zCl91 cJXmWeWz2vRprQP89ywuTbW02+UFAIHvY5gPuNCBGs7lcjZk1ibXC/uh5kFR5wr97MV57kwLQzPr1 rkrXOZK/RU/FS3xkrbAeteVEVlcl5HUL/lXjpC7KtHTCGol7g7kZovLCEGChlCXT43LuxlCj/ayHj BN1hufFw9WHOyW92U9lA==; Received: from localhost ([127.0.0.1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.92 #3 (Red Hat Linux)) id 1ho2ac-0007u6-27; Thu, 18 Jul 2019 09:20:38 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.92 #3 (Red Hat Linux)) id 1ho2aZ-0007tC-Ck for linux-arm-kernel@lists.infradead.org; Thu, 18 Jul 2019 09:20:36 +0000 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id EC5C128; Thu, 18 Jul 2019 02:20:32 -0700 (PDT) Received: from blommer (unknown [172.31.20.19]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 478A33F71A; Thu, 18 Jul 2019 02:20:30 -0700 (PDT) Date: Thu, 18 Jul 2019 10:20:23 +0100 From: Mark Rutland To: "Paul E. McKenney" Subject: Re: [PATCH 3/3] arm64: debug: Remove rcu_read_lock from debug exception Message-ID: <20190718092022.GA3625@blommer> References: <156342860634.8565.14804606041960884732.stgit@devnote2> <156342863822.8565.7624877983728871995.stgit@devnote2> <20190718062215.GG14271@linux.ibm.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20190718062215.GG14271@linux.ibm.com> User-Agent: Mutt/1.11.1+11 (2f07cb52) (2018-12-01) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20190718_022035_482910_4077B859 X-CRM114-Status: GOOD ( 18.68 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Dan Rue , Daniel Diaz , Anders Roxell , Catalin Marinas , Naresh Kamboju , Will Deacon , linux-kernel@vger.kernel.org, Masami Hiramatsu , linux-arm-kernel@lists.infradead.org, Matt Hart 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 Wed, Jul 17, 2019 at 11:22:15PM -0700, Paul E. McKenney wrote: > On Thu, Jul 18, 2019 at 02:43:58PM +0900, Masami Hiramatsu wrote: > > Remove rcu_read_lock()/rcu_read_unlock() from debug exception > > handlers since the software breakpoint can be hit on idle task. Why precisely do we need to elide these? Are we seeing warnings today? > The exception entry and exit use irq_enter() and irq_exit(), in this > case, correct? Otherwise RCU will be ignoring this CPU. This is missing today, which sounds like the underlying bug. Thanks, Mark. > > Thanx, Paul > > > Actually, we don't need it because those handlers run in exception > > context where the interrupts are disabled. This means those are never > > preempted. > > > > Reported-by: Naresh Kamboju > > Cc: Paul E. McKenney > > Signed-off-by: Masami Hiramatsu > > --- > > arch/arm64/kernel/debug-monitors.c | 14 ++++++++------ > > 1 file changed, 8 insertions(+), 6 deletions(-) > > > > diff --git a/arch/arm64/kernel/debug-monitors.c b/arch/arm64/kernel/debug-monitors.c > > index f8719bd30850..48222a4760c2 100644 > > --- a/arch/arm64/kernel/debug-monitors.c > > +++ b/arch/arm64/kernel/debug-monitors.c > > @@ -207,16 +207,16 @@ static int call_step_hook(struct pt_regs *regs, unsigned int esr) > > > > list = user_mode(regs) ? &user_step_hook : &kernel_step_hook; > > > > - rcu_read_lock(); > > - > > + /* > > + * Since single-step exception disables interrupt, this function is > > + * entirely not preemptible, and we can use rcu list safely here. > > + */ > > list_for_each_entry_rcu(hook, list, node) { > > retval = hook->fn(regs, esr); > > if (retval == DBG_HOOK_HANDLED) > > break; > > } > > > > - rcu_read_unlock(); > > - > > return retval; > > } > > NOKPROBE_SYMBOL(call_step_hook); > > @@ -305,14 +305,16 @@ static int call_break_hook(struct pt_regs *regs, unsigned int esr) > > > > list = user_mode(regs) ? &user_break_hook : &kernel_break_hook; > > > > - rcu_read_lock(); > > + /* > > + * Since brk exception disables interrupt, this function is > > + * entirely not preemptible, and we can use rcu list safely here. > > + */ > > list_for_each_entry_rcu(hook, list, node) { > > unsigned int comment = esr & ESR_ELx_BRK64_ISS_COMMENT_MASK; > > > > if ((comment & ~hook->mask) == hook->imm) > > fn = hook->fn; > > } > > - rcu_read_unlock(); > > > > return fn ? fn(regs, esr) : DBG_HOOK_ERROR; > > } > > _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel