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

Groups > linux.kernel > #1337382 > unrolled thread

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

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

  [PATCH 2/9] ARM: change NR_IPIS to 8 Arnd Bergmann <arnd@arndb.de> - 2016-02-18 15:10 +0100
    Re: [PATCH 2/9] ARM: change NR_IPIS to 8 Marc Zyngier <marc.zyngier@arm.com> - 2016-02-18 15:30 +0100
    Re: [PATCH 2/9] ARM: change NR_IPIS to 8 Russell King - ARM Linux <linux@arm.linux.org.uk> - 2016-02-18 15:40 +0100
      Re: [PATCH 2/9] ARM: change NR_IPIS to 8 Arnd Bergmann <arnd@arndb.de> - 2016-02-18 16:20 +0100

#1337382 — [PATCH 2/9] ARM: change NR_IPIS to 8

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.
To make the tracing work correctly, this extends the array by one
entry and increases NR_IPI accordingly.

This only works after patch e7273ff49acf ("ARM: 8488/1: Make
IPI_CPU_BACKTRACE a "non-secure" SGI"), which changed the number
assignment from '15' to '8'. If we decide to backport this patch
to stable kernels, we probably need to backport e7273ff49acf
as well.

As far as I can tell, the problem has existed since the tracepoints
were originally added, but it only triggered a gcc warning with the
later change to NR_IPIS.

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
---
 arch/arm/include/asm/hardirq.h | 2 +-
 arch/arm/kernel/smp.c          | 1 +
 2 files changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/arm/include/asm/hardirq.h b/arch/arm/include/asm/hardirq.h
index 3d7351c844aa..fe3ea776dc34 100644
--- a/arch/arm/include/asm/hardirq.h
+++ b/arch/arm/include/asm/hardirq.h
@@ -5,7 +5,7 @@
 #include <linux/threads.h>
 #include <asm/irq.h>
 
-#define NR_IPI	7
+#define NR_IPI	8
 
 typedef struct {
 	unsigned int __softirq_pending;
diff --git a/arch/arm/kernel/smp.c b/arch/arm/kernel/smp.c
index b4048e370730..d021566d71c2 100644
--- a/arch/arm/kernel/smp.c
+++ b/arch/arm/kernel/smp.c
@@ -482,6 +482,7 @@ static const char *ipi_types[NR_IPI] __tracepoint_string = {
 	S(IPI_CPU_STOP, "CPU stop interrupts"),
 	S(IPI_IRQ_WORK, "IRQ work interrupts"),
 	S(IPI_COMPLETION, "completion interrupts"),
+	S(IPI_CPU_BACKTRACE, "CPU backtrace"),
 };
 
 static void smp_cross_call(const struct cpumask *target, unsigned int ipinr)
-- 
2.7.0

[toc] | [next] | [standalone]

#1337393

Hi Arnd,

On 18/02/16 14:01, 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]);
> 
> This is a correct warning as we actually overflow the array here.
> To make the tracing work correctly, this extends the array by one
> entry and increases NR_IPI accordingly.
> 
> This only works after patch e7273ff49acf ("ARM: 8488/1: Make
> IPI_CPU_BACKTRACE a "non-secure" SGI"), which changed the number
> assignment from '15' to '8'. If we decide to backport this patch
> to stable kernels, we probably need to backport e7273ff49acf
> as well.

I may actually have made the bug worse in 89d798b ("ARM: 8487/1: Remove
IPI_CALL_FUNC_SINGLE"), which changed NR_IPI from 8 to 7. It would need
to be backported as well (as otherwise we don't have a free non-secure
IP slot).

> 
> As far as I can tell, the problem has existed since the tracepoints
> were originally added, but it only triggered a gcc warning with the
> later change to NR_IPIS.
> 
> 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

Acked-by: Marc Zyngier <marc.zyngier@arm.com>

Thanks,

	M.
-- 
Jazz is not dead. It just smells funny...

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

#1337419

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.

-- 
RMK's Patch system: http://www.arm.linux.org.uk/developer/patches/
FTTC broadband for 0.8mile line: currently at 9.6Mbps down 400kbps up
according to speedtest.net.

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

#1337454

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)

[toc] | [prev] | [standalone]

Back to top | Article view | linux.kernel

csiph-web