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=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,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 B9828C32751 for ; Wed, 31 Jul 2019 17:26:12 +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 8826120679 for ; Wed, 31 Jul 2019 17:26:11 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="onu+WnTB"; dkim=fail reason="signature verification failed" (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="Z+aVD4tL" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 8826120679 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org 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=CR5+dER8JnzSQaFeSpa+wnNIDdxCPv+k4P2g3Pz/0Z8=; b=onu+WnTBkTd1PZ bhIflndoCoEfsPIecsCZmg3Dff9WybTe81tMIRphmblqh9jdYzADOGkyfoo2DMUze9S436hglY5yC C4wcDAhqqV5DWe43XzawRELk1s1mY0hiNiPj5piIJZ9oj+travSJmyODy/PFpiDBYIpRAA6om5/ti Nltw9JERTPz1hgypKHLNn11BArNZNL/ZrUjLADp4w4Axx25UYZL/UXz1r2LsFBsDIIIua73xyjAMS 8avgTWjBlTjyZlfkYyzUbsD3dViQwRSICFrZgDwsCu4pmxLTjvkjkcycPSn3dbXg+eEeYfeLmpRkm YuVyNkmlv1rnR4gge0aw==; 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 1hssMd-0000JX-9W; Wed, 31 Jul 2019 17:26:11 +0000 Received: from mail.kernel.org ([198.145.29.99]) by bombadil.infradead.org with esmtps (Exim 4.92 #3 (Red Hat Linux)) id 1hssMa-0000JB-JM for linux-arm-kernel@lists.infradead.org; Wed, 31 Jul 2019 17:26:10 +0000 Received: from willie-the-truck (236.31.169.217.in-addr.arpa [217.169.31.236]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 4506F20679; Wed, 31 Jul 2019 17:26:06 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1564593968; bh=oELRU0Fx6RzT4m3ByuzMzmykJ4LlfkVxj9SOmJd+HeQ=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=Z+aVD4tLWZyYl6UDCZXR/2brEufSZdP249RJqnD8jlArFTVI/TUre1fn7uykA+bwG otIzSMKndxin46UKMd/OFppZfiXgHkp6ze0VzgPZyPn2zjWxQizsr47BYht8cfh6tR Joi0PkiHHix110PzZ5fJCj3LN41iThsGNUGkNh1g= Date: Wed, 31 Jul 2019 18:26:03 +0100 From: Will Deacon To: Masami Hiramatsu Subject: Re: [PATCH v3 3/4] arm64: Make debug exception handlers visible from RCU Message-ID: <20190731172602.36hdk3yb3w6uihbu@willie-the-truck> References: <156404254387.2020.886452004489353899.stgit@devnote2> <156404257493.2020.7940525305482369976.stgit@devnote2> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <156404257493.2020.7940525305482369976.stgit@devnote2> User-Agent: NeoMutt/20170113 (1.7.2) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20190731_102608_676269_13E56FAD X-CRM114-Status: GOOD ( 20.19 ) 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, Matt Hart , "Paul E . McKenney" , 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, Jul 25, 2019 at 05:16:15PM +0900, Masami Hiramatsu wrote: > Make debug exceptions visible from RCU so that synchronize_rcu() > correctly track the debug exception handler. > > This also introduces sanity checks for user-mode exceptions as same > as x86's ist_enter()/ist_exit(). > > The debug exception can interrupt in idle task. For example, it warns > if we put a kprobe on a function called from idle task as below. > The warning message showed that the rcu_read_lock() caused this > problem. But actually, this means the RCU is lost the context which > is already in NMI/IRQ. > > /sys/kernel/debug/tracing # echo p default_idle_call >> kprobe_events > /sys/kernel/debug/tracing # echo 1 > events/kprobes/enable > /sys/kernel/debug/tracing # [ 135.122237] > [ 135.125035] ============================= > [ 135.125310] WARNING: suspicious RCU usage > [ 135.125581] 5.2.0-08445-g9187c508bdc7 #20 Not tainted > [ 135.125904] ----------------------------- > [ 135.126205] include/linux/rcupdate.h:594 rcu_read_lock() used illegally while idle! > [ 135.126839] > [ 135.126839] other info that might help us debug this: > [ 135.126839] > [ 135.127410] > [ 135.127410] RCU used illegally from idle CPU! > [ 135.127410] rcu_scheduler_active = 2, debug_locks = 1 > [ 135.128114] RCU used illegally from extended quiescent state! > [ 135.128555] 1 lock held by swapper/0/0: > [ 135.128944] #0: (____ptrval____) (rcu_read_lock){....}, at: call_break_hook+0x0/0x178 > [ 135.130499] > [ 135.130499] stack backtrace: > [ 135.131192] CPU: 0 PID: 0 Comm: swapper/0 Not tainted 5.2.0-08445-g9187c508bdc7 #20 > [ 135.131841] Hardware name: linux,dummy-virt (DT) > [ 135.132224] Call trace: > [ 135.132491] dump_backtrace+0x0/0x140 > [ 135.132806] show_stack+0x24/0x30 > [ 135.133133] dump_stack+0xc4/0x10c > [ 135.133726] lockdep_rcu_suspicious+0xf8/0x108 > [ 135.134171] call_break_hook+0x170/0x178 > [ 135.134486] brk_handler+0x28/0x68 > [ 135.134792] do_debug_exception+0x90/0x150 > [ 135.135051] el1_dbg+0x18/0x8c > [ 135.135260] default_idle_call+0x0/0x44 > [ 135.135516] cpu_startup_entry+0x2c/0x30 > [ 135.135815] rest_init+0x1b0/0x280 > [ 135.136044] arch_call_rest_init+0x14/0x1c > [ 135.136305] start_kernel+0x4d4/0x500 > [ 135.136597] > > So make debug exception visible to RCU can fix this warning. > > Reported-by: Naresh Kamboju > Acked-by: Paul E. McKenney > Signed-off-by: Masami Hiramatsu > --- > Changes in v3: > - Make a comment for debug_exception_enter() clearer. > --- > arch/arm64/mm/fault.c | 40 ++++++++++++++++++++++++++++++++++++++++ > 1 file changed, 40 insertions(+) > > diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c > index 9568c116ac7f..ed6c55c87fdc 100644 > --- a/arch/arm64/mm/fault.c > +++ b/arch/arm64/mm/fault.c > @@ -777,6 +777,42 @@ void __init hook_debug_fault_code(int nr, > debug_fault_info[nr].name = name; > } > > +/* > + * In debug exception context, we explicitly disable preemption. Maybe add "despite having interrupts disabled"? > + * This serves two purposes: it makes it much less likely that we would > + * accidentally schedule in exception context and it will force a warning > + * if we somehow manage to schedule by accident. > + */ > +static void debug_exception_enter(struct pt_regs *regs) > +{ > + if (user_mode(regs)) { > + RCU_LOCKDEP_WARN(!rcu_is_watching(), "entry code didn't wake RCU"); > + } else { > + /* > + * We might have interrupted pretty much anything. In > + * fact, if we're a debug exception, we can even interrupt > + * NMI processing. We don't want this code makes in_nmi() > + * to return true, but we need to notify RCU. > + */ > + rcu_nmi_enter(); > + } > + > + preempt_disable(); If you're addingt new functions for entry/exit, maybe move the trace_hardirqs_{on,off}() calls in here too? Will _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel