From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752188AbbIOHPG (ORCPT ); Tue, 15 Sep 2015 03:15:06 -0400 Received: from mail113-248.mail.alibaba.com ([205.204.113.248]:41087 "EHLO us-alimail-mta1.hst.scl.en.alidc.net" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751414AbbIOHPD (ORCPT ); Tue, 15 Sep 2015 03:15:03 -0400 X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R201e4;FP=0|-1|-1|-1|0|-1|-1|-1;HT=e02c03307;MF=hillf.zj@alibaba-inc.com;NM=1;PH=DS;RN=3;SR=0; Reply-To: "Hillf Danton" From: "Hillf Danton" To: "'Daniel Thompson'" Cc: "linux-kernel" , References: <016701d0ef82$c303d6a0$490b83e0$@alibaba-inc.com> In-Reply-To: <016701d0ef82$c303d6a0$490b83e0$@alibaba-inc.com> Subject: RE: [PATCH] arm: Fix backtrace generation when IPI is masked Date: Tue, 15 Sep 2015 14:58:08 +0800 Message-ID: <017001d0ef83$e18a5d00$a49f1700$@alibaba-inc.com> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit X-Mailer: Microsoft Outlook 14.0 Thread-Index: AQFT9AKCQQbGB4ZDSA8woPqUCBbjNZ83HZHQ Content-Language: zh-cn Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > > Currently on ARM when is triggered from an interrupt handler > (e.g. a SysRq issued using UART or kbd) the main CPU will wedge for ten > seconds with interrupts masked before issuing a backtrace for every CPU > except itself. > > The new backtrace code introduced by commit 96f0e00378d4 ("ARM: add > basic support for on-demand backtrace of other CPUs") does not work > correctly when run from an interrupt handler because IPI_CPU_BACKTRACE > is used to generate the backtrace on all CPUs but cannot preempt the > current calling context. > > This can be fixed by detecting that the calling context cannot be > preempted and issuing the backtrace directly in this case. Some small > changes to the generic code are required to support this. > > Signed-off-by: Daniel Thompson > --- > arch/arm/kernel/smp.c | 7 +++++++ > lib/nmi_backtrace.c | 5 ++++- > 2 files changed, 11 insertions(+), 1 deletion(-) > > diff --git a/arch/arm/kernel/smp.c b/arch/arm/kernel/smp.c > index 48185a773852..4d8a80328c74 100644 > --- a/arch/arm/kernel/smp.c > +++ b/arch/arm/kernel/smp.c > @@ -748,6 +748,13 @@ core_initcall(register_cpufreq_notifier); > > static void raise_nmi(cpumask_t *mask) > { > + /* > + * Generate the backtrace directly if we are running in a > + * calling context that is not preemptible by the backtrace IPI. > + */ > + if (cpumask_test_cpu(smp_processor_id(), mask) && irqs_disabled()) > + nmi_cpu_backtrace(NULL); > + > smp_cross_call(mask, IPI_CPU_BACKTRACE); > } > > diff --git a/lib/nmi_backtrace.c b/lib/nmi_backtrace.c > index 88d3d32e5923..be0466a80d0b 100644 > --- a/lib/nmi_backtrace.c > +++ b/lib/nmi_backtrace.c > @@ -149,7 +149,10 @@ bool nmi_cpu_backtrace(struct pt_regs *regs) > /* Replace printk to write into the NMI seq */ > this_cpu_write(printk_func, nmi_vprintk); > pr_warn("NMI backtrace for cpu %d\n", cpu); > - show_regs(regs); > + if (regs) > + show_regs(regs); > + else > + dump_stack(); Better if dump_stack() is added in a separate patch, given that it is not mentioned in commit message. > this_cpu_write(printk_func, printk_func_save); > > cpumask_clear_cpu(cpu, to_cpumask(backtrace_mask)); > -- > 2.4.3