Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752221AbdHJDn3 (ORCPT ); Wed, 9 Aug 2017 23:43:29 -0400 Received: from szxga04-in.huawei.com ([45.249.212.190]:3488 "EHLO szxga04-in.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752022AbdHJDn2 (ORCPT ); Wed, 9 Aug 2017 23:43:28 -0400 Subject: Re: [PATCH v2] arm64: arch_timer: avoid infinite recursion when ftrace is enabled To: Mark Rutland , Marc Zyngier , Catalin Marinas , Will Deacon , LinuxArm , "linux-arm-kernel@lists.infradead.org" , "linux-kernel@vger.kernel.org" , Daniel Lezcano , Thomas Gleixner References: From: Ding Tianhong Message-ID: <88a09999-3b89-ea49-1565-22e3fa7fbd7c@huawei.com> Date: Thu, 10 Aug 2017 11:33:25 +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: 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=0001.0A090201.598BD412.0052,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: 760d2f8b002fd845481b4178b84f2ac9 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2151 Lines: 53 add Danial and Thomas. On 2017/8/10 10:52, Ding Tianhong wrote: > 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. > > This problem is similar to the fixed by upstream commit 96b3d28bf4 > ("sched/clock: Prevent tracing recursion in sched_clock_cpu()"). > > Fixes: 6acc71ccac71 ("arm64: arch_timer: Allows a CPU-specific erratum to only affect a subset of CPUs") > Signed-off-by: Ding Tianhong > Acked-by: Mark Rutland > Acked-by: Marc Zyngier > --- > 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); \ > } \ >