[v5,6/6] book3e/kgdb: Fix a single stgep case of lazy IRQ

When we're in kgdb_singlestep(), we have to work around to get
thread_info by copying from the kernel stack before calling
kgdb_handle_exception(), then copying it back afterwards.

But for PPC64, we have a lazy interrupt implementation. So after
copying thread info frome kernle stack, if we need to replay an
interrupt, we shouldn't restore that previous backup thread info
to make sure we can replay an interrupt lately with a proper
thread info.

This patch use __check_irq_replay() to guarantee this process.

Signed-off-by: Tiejun Chen <tiejun.chen@windriver.com>
---
 arch/powerpc/kernel/irq.c  |   10 ++++++++++
 arch/powerpc/kernel/kgdb.c |    3 ++-
 2 files changed, 12 insertions(+), 1 deletion(-)

On Thu, 2013-06-20 at 18:28 +0800, Tiejun Chen wrote:
> When we're in kgdb_singlestep(), we have to work around to get
> thread_info by copying from the kernel stack before calling
> kgdb_handle_exception(), then copying it back afterwards.
> 
> But for PPC64, we have a lazy interrupt implementation. So after
> copying thread info frome kernle stack, if we need to replay an
> interrupt, we shouldn't restore that previous backup thread info
> to make sure we can replay an interrupt lately with a proper
> thread info.

Explain why copying it would be a problem.

> This patch use __check_irq_replay() to guarantee this process.
> 
> Signed-off-by: Tiejun Chen <tiejun.chen@windriver.com>
> ---
>  arch/powerpc/kernel/irq.c  |   10 ++++++++++
>  arch/powerpc/kernel/kgdb.c |    3 ++-
>  2 files changed, 12 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/powerpc/kernel/irq.c b/arch/powerpc/kernel/irq.c
> index ea185e0..3625453 100644
> --- a/arch/powerpc/kernel/irq.c
> +++ b/arch/powerpc/kernel/irq.c
> @@ -339,7 +339,17 @@ bool prep_irq_for_idle(void)
>  	return true;
>  }
>  
> +notrace unsigned int check_irq_replay(void)
> +{
> +	return __check_irq_replay();
> +}
> +#else
> +notrace unsigned int check_irq_replay(void)
> +{
> +	return 0;
> +}
>  #endif /* CONFIG_PPC64 */
> +EXPORT_SYMBOL(check_irq_replay);
>  
>  int arch_show_interrupts(struct seq_file *p, int prec)
>  {
> diff --git a/arch/powerpc/kernel/kgdb.c b/arch/powerpc/kernel/kgdb.c
> index cde7818..5b30408 100644
> --- a/arch/powerpc/kernel/kgdb.c
> +++ b/arch/powerpc/kernel/kgdb.c
> @@ -152,6 +152,7 @@ static int kgdb_handle_breakpoint(struct pt_regs *regs)
>  }
>  
>  static DEFINE_PER_CPU(struct thread_info, kgdb_thread_info);
> +extern notrace unsigned int check_irq_replay(void);

Please put prototypes in headers rather than C files.  Also, "extern" is
unnecessary on function prototypes.

>  static int kgdb_singlestep(struct pt_regs *regs)
>  {
>  	struct thread_info *thread_info, *exception_thread_info;
> @@ -181,7 +182,7 @@ static int kgdb_singlestep(struct pt_regs *regs)
>  
>  	kgdb_handle_exception(0, SIGTRAP, 0, regs);
>  
> -	if (thread_info != exception_thread_info)
> +	if ((thread_info != exception_thread_info) && (!check_irq_replay()))

Unnecessary parentheses.

Are you sure it's safe to call this here?  Won't __check_irq_replay()
clear the pending event and PACA_IRQ_HARD_DIS?

-Scott

On 10/19/2013 07:32 AM, Scott Wood wrote:
> On Thu, 2013-06-20 at 18:28 +0800, Tiejun Chen wrote:
>> When we're in kgdb_singlestep(), we have to work around to get
>> thread_info by copying from the kernel stack before calling
>> kgdb_handle_exception(), then copying it back afterwards.
>>
>> But for PPC64, we have a lazy interrupt implementation. So after
>> copying thread info frome kernle stack, if we need to replay an
>> interrupt, we shouldn't restore that previous backup thread info
>> to make sure we can replay an interrupt lately with a proper
>> thread info.
>
> Explain why copying it would be a problem.
>

This would be gone away in next version as well :)

Thanks,

Tiejun