Re: [PATCH v9 1/2] ARM: avoid tracers in soft_restart

2014-04-14 Thread Sebastian Capella
Hi Will,

On 14 April 2014 03:53, Will Deacon  wrote:
> On Tue, Mar 18, 2014 at 09:40:57PM +, Sebastian Capella wrote:
>> Use of tracers in local_irq_disable is causes abort loops when called
>> with irqs disabled using a temporary stack.  Replace local_irq_disable
>> with raw_local_irq_disable instead to avoid tracers.
>
> Do you have any more information about these aborts? At the time we call
> local_irq_disable, the stack is still intact, so if the issue is simply
> related to having any tracers active at the call_with_stack invocation, we'd
> be better off disabling tracing here altogether.

This is specifically for when soft_restart is called in the
hibernation path with tracers enabled.  At that point, we've already
switched to a temporary stack, and when we call local_irq_disable,
we'll see this:

In the local_irq_disable, it ends up calling trace_hardirqs_off
(CONFIG_TRACE_IRQFLAGS_SUPPORT is enabled), which calls
trace_hardirqs_off_caller which checks lockdep_recursion in the
current task, but we've switched to a temporary stack with the
call_with_stack, and get_current is returning NULL.  This
triggers a data abort, which calls trace_hardirqs_off
again and so on.

We originally had a patch which added a soft restart called
soft_restart_noirq which avoided the irq disable.

You can see the discussion here:
https://patchwork.kernel.org/patch/3677591/

Thanks!

Sebastian
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Re: [PATCH v9 1/2] ARM: avoid tracers in soft_restart

2014-04-14 Thread Will Deacon
Hi Sebastian,

On Tue, Mar 18, 2014 at 09:40:57PM +, Sebastian Capella wrote:
> Use of tracers in local_irq_disable is causes abort loops when called
> with irqs disabled using a temporary stack.  Replace local_irq_disable
> with raw_local_irq_disable instead to avoid tracers.

Do you have any more information about these aborts? At the time we call
local_irq_disable, the stack is still intact, so if the issue is simply
related to having any tracers active at the call_with_stack invocation, we'd
be better off disabling tracing here altogether.

Will

> Signed-off-by: Sebastian Capella 
> Cc: Russell King 
> Cc: Andrew Morton 
> Cc: Will Deacon 
> Cc: Robin Holt 
> Cc: Thomas Gleixner 
> Cc: Konstantin Khlebnikov 
> Cc: Steven Capper 
> Cc: Stephen Warren 
> Cc: Tejun Heo 
> ---
>  arch/arm/kernel/process.c |2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/arm/kernel/process.c b/arch/arm/kernel/process.c
> index 92f7b15..f58b723 100644
> --- a/arch/arm/kernel/process.c
> +++ b/arch/arm/kernel/process.c
> @@ -100,7 +100,7 @@ void soft_restart(unsigned long addr)
>   u64 *stack = soft_restart_stack + ARRAY_SIZE(soft_restart_stack);
>  
>   /* Disable interrupts first */
> - local_irq_disable();
> + raw_local_irq_disable();
>   local_fiq_disable();
>  
>   /* Disable the L2 if we're the last man standing. */
> -- 
> 1.7.9.5
> 
> 
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Re: [PATCH v9 1/2] ARM: avoid tracers in soft_restart

2014-04-14 Thread Sebastian Capella
Hi Will,

On 14 April 2014 03:53, Will Deacon will.dea...@arm.com wrote:
 On Tue, Mar 18, 2014 at 09:40:57PM +, Sebastian Capella wrote:
 Use of tracers in local_irq_disable is causes abort loops when called
 with irqs disabled using a temporary stack.  Replace local_irq_disable
 with raw_local_irq_disable instead to avoid tracers.

 Do you have any more information about these aborts? At the time we call
 local_irq_disable, the stack is still intact, so if the issue is simply
 related to having any tracers active at the call_with_stack invocation, we'd
 be better off disabling tracing here altogether.

This is specifically for when soft_restart is called in the
hibernation path with tracers enabled.  At that point, we've already
switched to a temporary stack, and when we call local_irq_disable,
we'll see this:

In the local_irq_disable, it ends up calling trace_hardirqs_off
(CONFIG_TRACE_IRQFLAGS_SUPPORT is enabled), which calls
trace_hardirqs_off_caller which checks lockdep_recursion in the
current task, but we've switched to a temporary stack with the
call_with_stack, and get_current is returning NULL.  This
triggers a data abort, which calls trace_hardirqs_off
again and so on.

We originally had a patch which added a soft restart called
soft_restart_noirq which avoided the irq disable.

You can see the discussion here:
https://patchwork.kernel.org/patch/3677591/

Thanks!

Sebastian
--
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Re: [PATCH v9 1/2] ARM: avoid tracers in soft_restart

2014-04-14 Thread Will Deacon
Hi Sebastian,

On Tue, Mar 18, 2014 at 09:40:57PM +, Sebastian Capella wrote:
 Use of tracers in local_irq_disable is causes abort loops when called
 with irqs disabled using a temporary stack.  Replace local_irq_disable
 with raw_local_irq_disable instead to avoid tracers.

Do you have any more information about these aborts? At the time we call
local_irq_disable, the stack is still intact, so if the issue is simply
related to having any tracers active at the call_with_stack invocation, we'd
be better off disabling tracing here altogether.

Will

 Signed-off-by: Sebastian Capella sebastian.cape...@linaro.org
 Cc: Russell King li...@arm.linux.org.uk
 Cc: Andrew Morton a...@linux-foundation.org
 Cc: Will Deacon will.dea...@arm.com
 Cc: Robin Holt h...@sgi.com
 Cc: Thomas Gleixner t...@linutronix.de
 Cc: Konstantin Khlebnikov k.khlebni...@samsung.com
 Cc: Steven Capper steve.cap...@linaro.org
 Cc: Stephen Warren swar...@nvidia.com
 Cc: Tejun Heo t...@kernel.org
 ---
  arch/arm/kernel/process.c |2 +-
  1 file changed, 1 insertion(+), 1 deletion(-)
 
 diff --git a/arch/arm/kernel/process.c b/arch/arm/kernel/process.c
 index 92f7b15..f58b723 100644
 --- a/arch/arm/kernel/process.c
 +++ b/arch/arm/kernel/process.c
 @@ -100,7 +100,7 @@ void soft_restart(unsigned long addr)
   u64 *stack = soft_restart_stack + ARRAY_SIZE(soft_restart_stack);
  
   /* Disable interrupts first */
 - local_irq_disable();
 + raw_local_irq_disable();
   local_fiq_disable();
  
   /* Disable the L2 if we're the last man standing. */
 -- 
 1.7.9.5
 
 
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[PATCH v9 1/2] ARM: avoid tracers in soft_restart

2014-03-18 Thread Sebastian Capella
Use of tracers in local_irq_disable is causes abort loops when called
with irqs disabled using a temporary stack.  Replace local_irq_disable
with raw_local_irq_disable instead to avoid tracers.

Signed-off-by: Sebastian Capella 
Cc: Russell King 
Cc: Andrew Morton 
Cc: Will Deacon 
Cc: Robin Holt 
Cc: Thomas Gleixner 
Cc: Konstantin Khlebnikov 
Cc: Steven Capper 
Cc: Stephen Warren 
Cc: Tejun Heo 
---
 arch/arm/kernel/process.c |2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/arm/kernel/process.c b/arch/arm/kernel/process.c
index 92f7b15..f58b723 100644
--- a/arch/arm/kernel/process.c
+++ b/arch/arm/kernel/process.c
@@ -100,7 +100,7 @@ void soft_restart(unsigned long addr)
u64 *stack = soft_restart_stack + ARRAY_SIZE(soft_restart_stack);
 
/* Disable interrupts first */
-   local_irq_disable();
+   raw_local_irq_disable();
local_fiq_disable();
 
/* Disable the L2 if we're the last man standing. */
-- 
1.7.9.5

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[PATCH v9 1/2] ARM: avoid tracers in soft_restart

2014-03-18 Thread Sebastian Capella
Use of tracers in local_irq_disable is causes abort loops when called
with irqs disabled using a temporary stack.  Replace local_irq_disable
with raw_local_irq_disable instead to avoid tracers.

Signed-off-by: Sebastian Capella sebastian.cape...@linaro.org
Cc: Russell King li...@arm.linux.org.uk
Cc: Andrew Morton a...@linux-foundation.org
Cc: Will Deacon will.dea...@arm.com
Cc: Robin Holt h...@sgi.com
Cc: Thomas Gleixner t...@linutronix.de
Cc: Konstantin Khlebnikov k.khlebni...@samsung.com
Cc: Steven Capper steve.cap...@linaro.org
Cc: Stephen Warren swar...@nvidia.com
Cc: Tejun Heo t...@kernel.org
---
 arch/arm/kernel/process.c |2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/arm/kernel/process.c b/arch/arm/kernel/process.c
index 92f7b15..f58b723 100644
--- a/arch/arm/kernel/process.c
+++ b/arch/arm/kernel/process.c
@@ -100,7 +100,7 @@ void soft_restart(unsigned long addr)
u64 *stack = soft_restart_stack + ARRAY_SIZE(soft_restart_stack);
 
/* Disable interrupts first */
-   local_irq_disable();
+   raw_local_irq_disable();
local_fiq_disable();
 
/* Disable the L2 if we're the last man standing. */
-- 
1.7.9.5

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