From mboxrd@z Thu Jan 1 00:00:00 1970 From: hillf.zj@alibaba-inc.com (Hillf Danton) Date: Wed, 16 Sep 2015 10:43:41 +0800 Subject: [PATCH v3] arm: Fix backtrace generation when IPI is masked In-Reply-To: <1442328005-13661-1-git-send-email-daniel.thompson@linaro.org> References: <1442222294-2756-1-git-send-email-daniel.thompson@linaro.org> <1442328005-13661-1-git-send-email-daniel.thompson@linaro.org> Message-ID: <00d201d0f029$80210f40$80632dc0$@alibaba-inc.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.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. Issuing > directly leaves us without any pt_regs to pass to nmi_cpu_backtrace() > so we also modify the generic code to call dump_stack() when its > argument is NULL. > > Signed-off-by: Daniel Thompson > --- Acked-by: Hillf Danton > > Notes: > Changes in v3: > > * Added comments to describe how raise_nmi() and nmi_cpu_backtrace() > interact with backtrace_mask (Russell King). > > Changes in v2: > > * Improved commit message to better describe the changes to the generic > code (Hillf Danton). > > arch/arm/kernel/smp.c | 9 +++++++++ > lib/nmi_backtrace.c | 11 ++++++++++- > 2 files changed, 19 insertions(+), 1 deletion(-) > > diff --git a/arch/arm/kernel/smp.c b/arch/arm/kernel/smp.c > index 48185a773852..0c4e7fdb9636 100644 > --- a/arch/arm/kernel/smp.c > +++ b/arch/arm/kernel/smp.c > @@ -748,6 +748,15 @@ 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. Note > + * that nmi_cpu_backtrace() automatically removes the current cpu > + * from mask. > + */ > + 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..6019c53c669e 100644 > --- a/lib/nmi_backtrace.c > +++ b/lib/nmi_backtrace.c > @@ -43,6 +43,12 @@ static void print_seq_line(struct nmi_seq_buf *s, int start, int end) > printk("%.*s", (end - start) + 1, buf); > } > > +/* > + * When raise() is called it will be is passed a pointer to the > + * backtrace_mask. Architectures that call nmi_cpu_backtrace() > + * directly from their raise() functions may rely on the mask > + * they are passed being updated as a side effect of this call. > + */ > void nmi_trigger_all_cpu_backtrace(bool include_self, > void (*raise)(cpumask_t *mask)) > { > @@ -149,7 +155,10 @@ 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(); > this_cpu_write(printk_func, printk_func_save); > > cpumask_clear_cpu(cpu, to_cpumask(backtrace_mask)); > -- > 2.4.3 From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752182AbbIPCoE (ORCPT ); Tue, 15 Sep 2015 22:44:04 -0400 Received: from out4133-98.mail.aliyun.com ([42.120.133.98]:16699 "EHLO out4133-98.mail.aliyun.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751272AbbIPCoB (ORCPT ); Tue, 15 Sep 2015 22:44:01 -0400 X-Greylist: delayed 66196 seconds by postgrey-1.27 at vger.kernel.org; Tue, 15 Sep 2015 22:44:01 EDT X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R421e4;FP=0|-1|-1|-1|0|-1|-1|-1;HT=e02c03285;MF=hillf.zj@alibaba-inc.com;NM=1;PH=DS;RN=7;SR=0; Reply-To: "Hillf Danton" From: "Hillf Danton" To: "'Daniel Thompson'" , "'Russell King'" Cc: , , , , "'Thomas Gleixner'" References: <1442222294-2756-1-git-send-email-daniel.thompson@linaro.org> <1442328005-13661-1-git-send-email-daniel.thompson@linaro.org> In-Reply-To: <1442328005-13661-1-git-send-email-daniel.thompson@linaro.org> Subject: Re: [PATCH v3] arm: Fix backtrace generation when IPI is masked Date: Wed, 16 Sep 2015 10:43:41 +0800 Message-ID: <00d201d0f029$80210f40$80632dc0$@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: AQIUYg1/UTNmEiTRnRmZThfwAzT+NQMF0L/bnZ9fqPA= 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. Issuing > directly leaves us without any pt_regs to pass to nmi_cpu_backtrace() > so we also modify the generic code to call dump_stack() when its > argument is NULL. > > Signed-off-by: Daniel Thompson > --- Acked-by: Hillf Danton > > Notes: > Changes in v3: > > * Added comments to describe how raise_nmi() and nmi_cpu_backtrace() > interact with backtrace_mask (Russell King). > > Changes in v2: > > * Improved commit message to better describe the changes to the generic > code (Hillf Danton). > > arch/arm/kernel/smp.c | 9 +++++++++ > lib/nmi_backtrace.c | 11 ++++++++++- > 2 files changed, 19 insertions(+), 1 deletion(-) > > diff --git a/arch/arm/kernel/smp.c b/arch/arm/kernel/smp.c > index 48185a773852..0c4e7fdb9636 100644 > --- a/arch/arm/kernel/smp.c > +++ b/arch/arm/kernel/smp.c > @@ -748,6 +748,15 @@ 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. Note > + * that nmi_cpu_backtrace() automatically removes the current cpu > + * from mask. > + */ > + 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..6019c53c669e 100644 > --- a/lib/nmi_backtrace.c > +++ b/lib/nmi_backtrace.c > @@ -43,6 +43,12 @@ static void print_seq_line(struct nmi_seq_buf *s, int start, int end) > printk("%.*s", (end - start) + 1, buf); > } > > +/* > + * When raise() is called it will be is passed a pointer to the > + * backtrace_mask. Architectures that call nmi_cpu_backtrace() > + * directly from their raise() functions may rely on the mask > + * they are passed being updated as a side effect of this call. > + */ > void nmi_trigger_all_cpu_backtrace(bool include_self, > void (*raise)(cpumask_t *mask)) > { > @@ -149,7 +155,10 @@ 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(); > this_cpu_write(printk_func, printk_func_save); > > cpumask_clear_cpu(cpu, to_cpumask(backtrace_mask)); > -- > 2.4.3