[PATCH 2/9] ARM: change NR_IPIS to 8

[zhang.lyra@gmail.com (Chunyan Zhang)]

Hi,

Any conclusion on this patch? The coverity tool is still complaining
error on the issue which this patch can fix.

Thanks,
Chunyan

On 18 February 2016 at 23:18, Arnd Bergmann <arnd@arndb.de> wrote:
> On Thursday 18 February 2016 14:37:09 Russell King - ARM Linux wrote:
>> On Thu, Feb 18, 2016 at 03:01:54PM +0100, Arnd Bergmann wrote:
>> > When function tracing for IPIs is enabled, we get a warning for an
>> > overflow of the ipi_types array with the IPI_CPU_BACKTRACE type
>> > as triggered by raise_nmi():
>> >
>> > arch/arm/kernel/smp.c: In function 'raise_nmi':
>> > arch/arm/kernel/smp.c:489:2: error: array subscript is above array bounds [-Werror=array-bounds]
>> >   trace_ipi_raise(target, ipi_types[ipinr]);
>>
>> We really don't want to treat the backtrace IPI as a normal IPI at all -
>> we want it to invoke the least amount of code possible.  Hence this code
>> which avoids the issue:
>>
>>         if ((unsigned)ipinr < NR_IPI) {
>>                 trace_ipi_entry_rcuidle(ipi_types[ipinr]);
>>                 __inc_irq_stat(cpu, ipi_irqs[ipinr]);
>>         }
>>
>> However, what's missing is that the addition of tracing here missed
>> that CPU_BACKTRACE is not to be traced.  The call in raise_nmi()
>> should have been converted to __smp_cross_call() to avoid the
>> tracing code.
>
> I've replaced the patch locally with the version below now, and
> will throw it into the randconfig build test infrastructure to
> make sure I didn't screw up in an obvious way here.
>
>         Arnd
>
> From 7528c9b0558fdf4de785e62e61f0dd2ffe874110 Mon Sep 17 00:00:00 2001
> From: Arnd Bergmann <arnd@arndb.de>
> Date: Sun, 31 Jan 2016 22:26:21 +0100
> Subject: [PATCH] ARM: prevent tracing IPI_CPU_BACKTRACE
>
> When function tracing for IPIs is enabled, we get a warning for an
> overflow of the ipi_types array with the IPI_CPU_BACKTRACE type
> as triggered by raise_nmi():
>
> arch/arm/kernel/smp.c: In function 'raise_nmi':
> arch/arm/kernel/smp.c:489:2: error: array subscript is above array bounds [-Werror=array-bounds]
>   trace_ipi_raise(target, ipi_types[ipinr]);
>
> This is a correct warning as we actually overflow the array here.
>
> This patch raise_nmi() to call __smp_cross_call() instead of
> smp_cross_call(), to avoid calling into ftrace. For clarification,
> I'm also adding a two new code comments describing how this one
> is special.
>
> The warning appears to have shown up after patch e7273ff49acf
> ("ARM: 8488/1: Make IPI_CPU_BACKTRACE a "non-secure" SGI"), which
> changed the number assignment from '15' to '8', but as far as I can
> tell has existed since the IPI tracepoints were first introduced.
> If we decide to backport this patch to stable kernels, we probably
> need to backport e7273ff49acf as well.
>
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> Fixes: e7273ff49acf ("ARM: 8488/1: Make IPI_CPU_BACKTRACE a "non-secure" SGI")
> Fixes: 365ec7b17327 ("ARM: add IPI tracepoints") # v3.17
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
>
> diff --git a/arch/arm/include/asm/hardirq.h b/arch/arm/include/asm/hardirq.h
> index 3d7351c844aa..2fd0a2619b0b 100644
> --- a/arch/arm/include/asm/hardirq.h
> +++ b/arch/arm/include/asm/hardirq.h
> @@ -5,6 +5,7 @@
>  #include <linux/threads.h>
>  #include <asm/irq.h>
>
> +/* number of IPIS _not_ including IPI_CPU_BACKTRACE */
>  #define NR_IPI 7
>
>  typedef struct {
> diff --git a/arch/arm/kernel/smp.c b/arch/arm/kernel/smp.c
> index b4048e370730..9802a94260db 100644
> --- a/arch/arm/kernel/smp.c
> +++ b/arch/arm/kernel/smp.c
> @@ -72,6 +72,10 @@ enum ipi_msg_type {
>         IPI_CPU_STOP,
>         IPI_IRQ_WORK,
>         IPI_COMPLETION,
> +       /*
> +        * CPU_BACKTRACE is special and not included in NR_IPI
> +        * or tracable with trace_ipi_*
> +        */
>         IPI_CPU_BACKTRACE,
>         /*
>          * SGI8-15 can be reserved by secure firmware, and thus may
> @@ -757,7 +761,7 @@ static void raise_nmi(cpumask_t *mask)
>         if (cpumask_test_cpu(smp_processor_id(), mask) && irqs_disabled())
>                 nmi_cpu_backtrace(NULL);
>
> -       smp_cross_call(mask, IPI_CPU_BACKTRACE);
> +       __smp_cross_call(mask, IPI_CPU_BACKTRACE);
>  }
>
>  void arch_trigger_all_cpu_backtrace(bool include_self)
>
>
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