Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > linux.kernel > #1224718 > unrolled thread

RE: [PATCH] arm: Fix backtrace generation when IPI is masked

Back to article view | Back to linux.kernel

This discussion starts older than the indexed window; earlier articles aren't shown. The article labeled Started by below is the oldest one visible, not the original post.

Contents

  RE: [PATCH] arm: Fix backtrace generation when IPI is masked "Hillf Danton" <hillf.zj@alibaba-inc.com> - 2015-09-15 09:20 +0200
    Re: [PATCH] arm: Fix backtrace generation when IPI is masked Daniel Thompson <daniel.thompson@linaro.org> - 2015-09-15 10:20 +0200
      RE: [PATCH] arm: Fix backtrace generation when IPI is masked "Hillf Danton" <hillf.zj@alibaba-inc.com> - 2015-09-15 10:30 +0200

#1224718 — RE: [PATCH] arm: Fix backtrace generation when IPI is masked

> 
> Currently on ARM when <SysRq-L> 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 <daniel.thompson at linaro.org>
> ---
>  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

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/

[toc] | [next] | [standalone]

#1224750

On 15/09/15 07:58, Hillf Danton wrote:
>> Currently on ARM when <SysRq-L> 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 <daniel.thompson at linaro.org>
>> ---
>>   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.

Adding dump_stack() is mentioned in passing ("Some small changes to the 
generic code are required to support this.") but you're right that the 
reason for the change is not explicitly called out.

I can certainly respin as two patches but perhaps its better just to 
improve the commit message. Something like:

 > 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().
 > Modify the generic code to call dump_stack() when its argument is
 > NULL.

Which do you prefer?


Daniel.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/

[toc] | [prev] | [next] | [standalone]

#1224755

> > Better if dump_stack() is added in a separate patch, given that
> > it is not mentioned in commit message.
> 
> Adding dump_stack() is mentioned in passing ("Some small changes to the
> generic code are required to support this.") but you're right that the
> reason for the change is not explicitly called out.
> 
> I can certainly respin as two patches but perhaps its better just to
> improve the commit message. Something like:
> 
>  > 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().
>  > Modify the generic code to call dump_stack() when its argument is
>  > NULL.
> 
Looks nice!

thanks
Hillf

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/

[toc] | [prev] | [standalone]

Back to top | Article view | linux.kernel

csiph-web