Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751595AbdGZCnR (ORCPT ); Tue, 25 Jul 2017 22:43:17 -0400 Received: from szxga01-in.huawei.com ([45.249.212.187]:10269 "EHLO szxga01-in.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750851AbdGZCnP (ORCPT ); Tue, 25 Jul 2017 22:43:15 -0400 Subject: Re: [PATCH RESEND] arm64: arch_timer: fix the infinite recursion when enable ftrace and erratum workaround To: Mark Rutland , Marc Zyngier , Daniel Lezcano , Thomas Gleixner References: <321e4c16-aa14-beee-b6dc-36e19e5ec35a@huawei.com> <20170710112229.GA18040@leverpostej> CC: Catalin Marinas , Will Deacon , LinuxArm , "linux-arm-kernel@lists.infradead.org" , "linux-kernel@vger.kernel.org" From: Ding Tianhong Message-ID: <5f7566b3-a2ca-b882-89e1-dcaaaec79fcd@huawei.com> Date: Wed, 26 Jul 2017 10:42:49 +0800 User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:45.0) Gecko/20100101 Thunderbird/45.4.0 MIME-Version: 1.0 In-Reply-To: <20170710112229.GA18040@leverpostej> Content-Type: text/plain; charset="windows-1252" Content-Transfer-Encoding: 7bit X-Originating-IP: [10.177.23.32] X-CFilter-Loop: Reflected X-Mirapoint-Virus-RAPID-Raw: score=unknown(0), refid=str=0001.0A090205.597801B8.0018,ss=1,re=0.000,recu=0.000,reip=0.000,cl=1,cld=1,fgs=0, ip=0.0.0.0, so=2014-11-16 11:51:01, dmn=2013-03-21 17:37:32 X-Mirapoint-Loop-Id: c4160f1e7887b810375d53f5b7b054c2 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3485 Lines: 100 On 2017/7/10 19:22, Mark Rutland wrote: > On Sun, Jul 09, 2017 at 04:30:54PM +0800, Ding Tianhong wrote: >> When enable preempt and debug ftrace, and perform the following steps, the >> system will hang: >> mount -t debugfs nodev /sys/kernel/debug/ >> cd /sys/kernel/debug/tracing/ >> echo function_graph > current_tracer >> >> This is because tracing the preempt_disable/enable calls would cause >> trace_clock() which would get local timer to go into infinite recursion >> when enable the arch timer erratum workaround for some chips, so Prevent >> tracing of preempt_disable/enable() in arch_timer_reg_read_stable(). >> >> This problem is similar to the fixed by upstream commit 96b3d28bf4 >> ("sched/clock: Prevent tracing recursion in sched_clock_cpu()"). > > As I mentioned before, the patch itself looks fine to me, but the commit > message is somewhat difficult to read. > > Can we please change this to: > > arm64: arch_timer: avoid infinite recursion when ftrace is enabled > > On platforms with an arch timer erratum workaround, it's possible for > arch_timer_reg_read_stable() to recurse into itself when certain > tracing options are enabled, leading to stack overflows and related > problems. > > For example, when PREEMPT_TRACER and FUNCTION_GRAPH_TRACER are > selected, it's possible to trigger this with: > > $ mount -t debugfs nodev /sys/kernel/debug/ > $ echo function_graph > /sys/kernel/debug/tracing/current_tracer > > The problem is that in such cases, preempt_disable() instrumentation > attempts to acquire a timestamp via trace_clock(), resulting in a call > back to arch_timer_reg_read_stable(), and hence recursion. > > This patch changes arch_timer_reg_read_stable() to use > preempt_{disable,enable}_notrace(), which avoids this. > > With that commit message: > > Acked-by: Mark Rutland > > Daniel, Thomas, would you be happy to fold that in when picking this? Or > would you prefer that I fix this up and resend? > Hi Danial, Thomas: It looks didn't merge to the mainline tree yet, should I update the commit and resend this patch again? Thanks Ding > Thanks, > Mark. > >> Fixes: 6acc71ccac71 ("arm64: arch_timer: Allows a CPU-specific erratum to only affect a subset of CPUs") >> Signed-off-by: Ding Tianhong >> --- >> arch/arm64/include/asm/arch_timer.h | 4 ++-- >> 1 file changed, 2 insertions(+), 2 deletions(-) >> >> diff --git a/arch/arm64/include/asm/arch_timer.h b/arch/arm64/include/asm/arch_timer.h >> index 74d08e4..67bb7a4 100644 >> --- a/arch/arm64/include/asm/arch_timer.h >> +++ b/arch/arm64/include/asm/arch_timer.h >> @@ -65,13 +65,13 @@ struct arch_timer_erratum_workaround { >> u64 _val; \ >> if (needs_unstable_timer_counter_workaround()) { \ >> const struct arch_timer_erratum_workaround *wa; \ >> - preempt_disable(); \ >> + preempt_disable_notrace(); \ >> wa = __this_cpu_read(timer_unstable_counter_workaround); \ >> if (wa && wa->read_##reg) \ >> _val = wa->read_##reg(); \ >> else \ >> _val = read_sysreg(reg); \ >> - preempt_enable(); \ >> + preempt_enable_notrace(); \ >> } else { \ >> _val = read_sysreg(reg); \ >> } \ >> -- >> 1.9.0 >> >> > > _______________________________________________ > linux-arm-kernel mailing list > linux-arm-kernel@lists.infradead.org > http://lists.infradead.org/mailman/listinfo/linux-arm-kernel > > . >