[PATCH 2/2] arm64: Add dump_backtrace() in show_regs

[Mark Rutland]

On Mon, May 08, 2017 at 09:56:55PM +0800, Kefeng Wang wrote:
> When the system trigger a softlockup(eg, infinite loop when
> PREEMPT_NONE), it only shows regs without stack trace, which
> makes it difficult to adress the issue.

How about:

  Generic code expects show_regs() to dump the stack, but arm64's
  show_regs() does not. This makes it hard to debug softlockups and
  other issues that reesult in show_regs() being called.

  This patch updates arm64's show_regs() to dump the stack, as common
  code expects.

> Signed-off-by: Kefeng Wang <wangkefeng.wang at huawei.com>
> ---
>  arch/arm64/include/asm/stacktrace.h | 1 +
>  arch/arm64/kernel/process.c         | 1 +
>  arch/arm64/kernel/traps.c           | 2 +-
>  3 files changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/arm64/include/asm/stacktrace.h b/arch/arm64/include/asm/stacktrace.h
> index 801a16db..5b6eafc 100644
> --- a/arch/arm64/include/asm/stacktrace.h
> +++ b/arch/arm64/include/asm/stacktrace.h
> @@ -30,5 +30,6 @@ struct stackframe {
>  extern int unwind_frame(struct task_struct *tsk, struct stackframe *frame);
>  extern void walk_stackframe(struct task_struct *tsk, struct stackframe *frame,
>  			    int (*fn)(struct stackframe *, void *), void *data);
> +extern void dump_backtrace(struct pt_regs *regs, struct task_struct *tsk);
>  
>  #endif	/* __ASM_STACKTRACE_H */
> diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c
> index ae2a835..af1ea25 100644
> --- a/arch/arm64/kernel/process.c
> +++ b/arch/arm64/kernel/process.c
> @@ -210,6 +210,7 @@ void __show_regs(struct pt_regs *regs)
>  void show_regs(struct pt_regs * regs)
>  {
>  	__show_regs(regs);
> +	dump_backtrace(regs, NULL);
>  }

I believe that as we pass the regs down, this should trigger the frame
skipping that we want, as I mentioned in reply to v1 [1].

So FWIW, with the commit message fixup:

Acked-by: Mark Rutland <mark.rutland at arm.com>

Thanks,
Mark.

[1] http://lists.infradead.org/pipermail/linux-arm-kernel/2017-March/496377.html

>  static void tls_thread_flush(void)
> diff --git a/arch/arm64/kernel/traps.c b/arch/arm64/kernel/traps.c
> index d4d6ae0..368c3c8 100644
> --- a/arch/arm64/kernel/traps.c
> +++ b/arch/arm64/kernel/traps.c
> @@ -140,7 +140,7 @@ static void dump_instr(const char *lvl, struct pt_regs *regs)
>  	}
>  }
>  
> -static void dump_backtrace(struct pt_regs *regs, struct task_struct *tsk)
> +void dump_backtrace(struct pt_regs *regs, struct task_struct *tsk)
>  {
>  	struct stackframe frame;
>  	unsigned long irq_stack_ptr;
> -- 
> 1.7.12.4
>