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=-8.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS 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 D5E31C2D0E4 for ; Fri, 20 Nov 2020 15:22:10 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 24B172245A for ; Fri, 20 Nov 2020 15:22:09 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 24B172245A Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 524776B005D; Fri, 20 Nov 2020 10:22:09 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 4D4656B006C; Fri, 20 Nov 2020 10:22:09 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 39C066B006E; Fri, 20 Nov 2020 10:22:09 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0198.hostedemail.com [216.40.44.198]) by kanga.kvack.org (Postfix) with ESMTP id 0C3C66B005D for ; Fri, 20 Nov 2020 10:22:08 -0500 (EST) Received: from smtpin15.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay03.hostedemail.com (Postfix) with ESMTP id 9ABD8824999B for ; Fri, 20 Nov 2020 15:22:08 +0000 (UTC) X-FDA: 77505162336.15.spot81_001407e2734c Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin15.hostedemail.com (Postfix) with ESMTP id 66E8A1814B0CA for ; Fri, 20 Nov 2020 15:22:08 +0000 (UTC) X-HE-Tag: spot81_001407e2734c X-Filterd-Recvd-Size: 4149 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by imf20.hostedemail.com (Postfix) with ESMTP for ; Fri, 20 Nov 2020 15:22:07 +0000 (UTC) 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 C1C0311D4; Fri, 20 Nov 2020 07:22:06 -0800 (PST) Received: from C02TD0UTHF1T.local (unknown [10.57.27.176]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 2DEEF3F70D; Fri, 20 Nov 2020 07:22:02 -0800 (PST) Date: Fri, 20 Nov 2020 15:22:00 +0000 From: Mark Rutland To: "Paul E. McKenney" Cc: Marco Elver , Steven Rostedt , Anders Roxell , Andrew Morton , Alexander Potapenko , Dmitry Vyukov , Jann Horn , Linux Kernel Mailing List , Linux-MM , kasan-dev , rcu@vger.kernel.org, Peter Zijlstra , Tejun Heo , Lai Jiangshan , linux-arm-kernel@lists.infradead.org Subject: Re: linux-next: stall warnings and deadlock on Arm64 (was: [PATCH] kfence: Avoid stalling...) Message-ID: <20201120152200.GD2328@C02TD0UTHF1T.local> References: <20201118225621.GA1770130@elver.google.com> <20201118233841.GS1437@paulmck-ThinkPad-P72> <20201119125357.GA2084963@elver.google.com> <20201119151409.GU1437@paulmck-ThinkPad-P72> <20201119170259.GA2134472@elver.google.com> <20201119184854.GY1437@paulmck-ThinkPad-P72> <20201119193819.GA2601289@elver.google.com> <20201119213512.GB1437@paulmck-ThinkPad-P72> <20201120141928.GB3120165@elver.google.com> <20201120143928.GH1437@paulmck-ThinkPad-P72> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20201120143928.GH1437@paulmck-ThinkPad-P72> X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Fri, Nov 20, 2020 at 06:39:28AM -0800, Paul E. McKenney wrote: > On Fri, Nov 20, 2020 at 03:19:28PM +0100, Marco Elver wrote: > > I found that disabling ftrace for some of kernel/rcu (see below) solved > > the stalls (and any mention of deadlocks as a side-effect I assume), > > resulting in successful boot. > > > > Does that provide any additional clues? I tried to narrow it down to 1-2 > > files, but that doesn't seem to work. > > There were similar issues during the x86/entry work. Are the ARM guys > doing arm64/entry work now? I'm currently looking at it. I had been trying to shift things to C for a while, and right now I'm trying to fix the lockdep state tracking, which is requiring untangling lockdep/rcu/tracing. The main issue I see remaining atm is that we don't save/restore the lockdep state over exceptions taken from kernel to kernel. That could result in lockdep thinking IRQs are disabled when they're actually enabled (because code in the nested context might do a save/restore while IRQs are disabled, then return to a context where IRQs are enabled), but AFAICT shouldn't result in the inverse in most cases since the non-NMI handlers all call lockdep_hardirqs_disabled(). I'm at a loss to explaim the rcu vs ftrace bits, so if you have any pointers to the issuies ween with the x86 rework that'd be quite handy. Thanks, Mark. > > Thanx, Paul > > > Thanks, > > -- Marco > > > > ------ >8 ------ > > > > diff --git a/kernel/rcu/Makefile b/kernel/rcu/Makefile > > index 0cfb009a99b9..678b4b094f94 100644 > > --- a/kernel/rcu/Makefile > > +++ b/kernel/rcu/Makefile > > @@ -3,6 +3,13 @@ > > # and is generally not a function of system call inputs. > > KCOV_INSTRUMENT := n > > > > +ifdef CONFIG_FUNCTION_TRACER > > +CFLAGS_REMOVE_update.o = $(CC_FLAGS_FTRACE) > > +CFLAGS_REMOVE_sync.o = $(CC_FLAGS_FTRACE) > > +CFLAGS_REMOVE_srcutree.o = $(CC_FLAGS_FTRACE) > > +CFLAGS_REMOVE_tree.o = $(CC_FLAGS_FTRACE) > > +endif > > + > > ifeq ($(CONFIG_KCSAN),y) > > KBUILD_CFLAGS += -g -fno-omit-frame-pointer > > endif